“Flowers,” I declaim from my soapbox, “are overrepresented in the attention economy! Plant social media is in the tank for Big Blossom! Justice for sedges and grasses!” I shake my cardboard placard at an unsuspecting passerby, who accelerates, leaning away from me. “Enough bloomscrolling! More Poace-ting!”

Okay, I’ll workshop the hashtag. But the point is that while flowers are the charismatic representatives of the plant world, grasses also flower, some of them quite ostentatiously. Purple lovegrass is one such grass. In late summer, it conjures a purplish pink haze above its foliage that lasts into the fall. Its bloom looks a little like a firework’s stars frozen in time, just after they’ve lost their definition and are falling back to earth.

The purple sticks around for a while, too. What’s catching our eyes are the spikelets, or tiny flower clusters that make up this plant’s bloom. If you get a chance, zoom in on one–you know, with your robot vision. Or a handy phone camera. (You may have to place the spikelet against your hand or a piece of paper to get the camera to focus.)

Purple lovegrass spikelets have a stack of tiny florets. A floret is essentially a grass flower. They’re wrapped in lemmas, little leaf tissues that protect the floret. At the base of the spikelet are a pair of glumes, which are a little like lemmas that don’t contain any florets. For our purposes, what’s important is that all of these are tiny and vibrantly purple.

The spikelets are held aloft on panicles, a flower structure where the main stem has branches, and those branches have branches, and those branches also have branches made for spikelets (pedicels). (Cue the Xzibit meme.) The bloom can raise the plant’s full height to near two feet.

Grass ID is difficult at best when a plant isn’t flowering. This plant’s biggest tell is probably a band of quarter-inch-long white hairs where the leaf bends away from the stem.

The leaves themselves grow to about a foot long at most (30 cm) and taper to a point. They extend out from a central crown: purple lovegrass is a bunch grass, or a grass that grows in clumps. In the fall, the leaves turn coppery, and then tan with the first real frost.

Native range

Eragrostis spectabilis has a huge native range, covering most of the contiguous U.S. from east to west, absent only from (most of) the west coast and the Great Basin. It’s also present in Canada and Mexico. It’s able to make a living, as they say, in all these places through being opportunistic. It’s found ways to tolerate drought, salt, and poor soil—but it’s easily outcompeted.

Habitat

Gardeners: this plant thinks you use too much compost. Stop fertilizing, it says. You’re promoting my competition.

Literature on restoration treats purple lovegrass as an early succession species, meaning it’s one of the first to grow on ground where other plants can’t.

It’s been studied for its potential role as fuel for fires in pine savannas in the southeastern U.S. Fire plays an important role in these ecosystems, burning back woody sprouts and seedlings to prevent the forest canopy from closing. This allows enough light for grasses and flowers to grow.

Purple lovegrass, it turns out, provides really good fuel for fires. It was one of the “top performers” in one study where researchers lit a bunch of native grasses on fire (and I’m sure they were shouting “for science!” while they did it). The point of the study, pyrotechnics aside, was to learn which native grasses might be a good fit for restoration work in areas that depend on fire. Purple lovegrass, apparently, is a good candidate.

Perhaps confusingly, the ability to grow in seemingly hostile soils and environments doesn’t translate into “spreads maniacally.” Purple lovegrass is easily outcompeted by taller plants. As soon as it’s shaded, it folds. That comes with the gig of being an early successional species. So you can think of it as being exiled to the least desirable real estate, the kind with the most disruption and disturbance.

One benefit of being “disturbance-adapted” is that it does quite well near people, since we tend to do a lot of disturbing. We dig things up, cut things down, mow our lawns, throw salt all over the place, etc. And in doing so we make lots of the kind of habitat that purple lovegrass likes. It might not make a good lawn, but it would be happy to be part of your lawn. As long as you don’t water too much. Or fertilize. Or do much of anything except mow down the taller species.

Who it feeds and shelters

This plant’s wildlife associations are a little hazy, a bit like its panicles. Illinois Wildflowers, usually a trustworthy source, says it’s the larval host for the Zabulon skipper (Lon zabulon).

A small leafhopper, Flexamia areolata, specializes on purple lovegrass, too. A leafhopper is an insect that sucks the juices from plant leaves. If you’re wondering why you should care about a leafhopper, the usual answer among ecological gardeners is, “it’s a valuable food for other animals.” Some leafhoppers are quite striking, though this one’s a fairly drab brownish color. (Sorry leafhopper fans, I’m likely not doing it justice here.)

Unfortunately, there aren’t many others to name confidently. Most datasets associate insects with the genus, Eragrostis, not with the species. For example, Doug Tallamy and Kimberly Shropshire’s data only list six species associated with the genus, and the HOSTS database lists even fewer within this plant’s native range. It’s similarly not a major food source for birds. The Avian Diet Database only lists a few birds that eat the seeds of Eragrostis species generally. So maybe it supports wild turkeys? Even an aphids dataset didn’t list this plant as a specific aphid food, and I sort of thought aphids ate everything.

How it spreads

Purple lovegrass is a warm season grass, meaning it shows up when the soil gets warm enough. It gets going around the same time crabgrass does.

It begins sending up its panicle in August, and the seeds mature into October. When they’re ready, the panicle breaks off and, I imagine, launches itself into the wind, shedding seeds as it tumbleweeds along. Sort of like a schoolbus dropping the kids off. This is why one of its common names is tumblegrass.

It may also spread slowly by short rhizomes, or underground, horizontal stems that pop up nearby and make new plants. This has the effect of expanding the clump size over time.

These methods of spreading may make one think, oh, perhaps this plant might be good for a native lawn. And some of the nurseries that sell it do include images that seem to confirm this. But I’m skeptical. As a bunch grass, this plant’s likely to leave lots of space between its initial clumps. Over time, those clumps might knit together, but I doubt they’d have a chance; crabgrass and other opportunistic plants would happily find a home in the crevices. And purple lovegrass is not particularly competitive. During a cool, wet season, clover and other mat-forming lawn denizens might well crowd it out entirely.

How people have used it

It’s sold as an ornamental grass. That’s about all I could find. People don’t even make tea with it, as far as I can tell. And people make tea out of everything.

(If you do know of a way that people have used it, please let me know!)

Plants in Plain Language is free. Subscribe to get fun and plant nerdery in your inbox.

You can also help me rationalize spending even more time on this—writing, researching, trying to get photos of very spontaneous bees—by buying me a coffee or becoming a monthly sponsor.

Had our argument continued, I might’ve said my interlocutor was conflating “invasive” with “annoys me.” I’m sympathetic to this, since “invasive” is an intuitive way to describe plants that show up in your garden fully caffeinated and set about taking over. Unfortunately, I don’t think it’s very useful. For example, I would personally prefer if there were more blue violets and less grass in the average American lawn. In our argument, what’s “invasive” boils down to Yeah? Well That’s Just, Like, Your Opinion, Man.

So what exactly does it mean for a plant to be invasive?

A better, if still a little vague, definition of “invasive”

A 1999 Executive Order signed by then-President Bill Clinton defines invasive species (not just invasive plants) as those “whose introduction does or is likely to cause economic or environmental harm or harm to human health.”

The order also created an Invasive Species Council whose members were tasked with “provid[ing] national leadership regarding invasive species.” In practice, this means coordinating between and developing guidance for other agencies and levels of government. And that’s mostly what they’ve produced, though it’s not clear to me that the work’s been prioritized or funded recently. This shouldn’t be surprising; an executive order has less oomph behind it than real legislation, and “invasive species” isn’t exactly the most politically salient topic in the U.S.

That said, Clinton’s definition is clearer than the one you’d try to iron out based on my argument with Some Guy online. At least it includes “tests”: a plant’s invasive if it’s introduced and if it causes economic or ecological harm.

The invasion biology perspective

The academic discipline of invasion biology studies what happens (and how) when a species is introduced, usually by humans, to a new environment. Its practitioners focus on what effects these species have, if any, on local wildlife, habitat, ecology, etc. I’m only going to brush the surface of this discipline here. But the perspective it provides is useful, since its members have argued vigorously about what it means to be invasive and how to assess the consequences of invasion.

Invasion biologists usefully separate the ideas of “invasion” and “impact.” (Grammar snobs, hold your noses.) In an important paper in the field, Richardson and colleagues (2000) write that the word invasive should be about spread, i.e. the degree, distance, speed, etc. They argue that a separate category, “transformers,” should be reserved for the “10% of invasive plants that change the character, condition, form, or nature of ecosystems over substantial areas.”

To be clear, the species Richardson and his co-authors are calling “transformers” are the ones the executive order seems to be calling “invasive.” Both also agree that to be invasive one must have been introduced to an area through human activity. And later invasion biology work involved creating scoring systems for assessing how transformative a species was to the environment it was introduced in. For example, Blackburn et al. (2014) and Hawkins et al. (2015) produced the Environmental Impact Classification for Alien Taxa (EICAT) framework. The purpose of EICAT is to help researchers measure how much an introduced species has affected its new environment.

Richardson and his co-authors also point out that invasion evokes concepts like “aggression, assault…infringement, intrusion, onslaught, raid, etc.” And thus they think we should just use “weed” for undesirable plants. (I sympathize with this view, though I think it runs smack into lawn culture. I’d like separate categories for “harms ecosystems” and “harms lawns.”)

I didn’t know much about invasion biology before I started researching this piece. I learned the term “invasive” from native plant advocates, who are generally focused on the harm that introduced plants cause. But Richardson and his co-authors focus on if a species’ can not only survive but reproduce and spread in their new environments. For example, they propose that we use “invasion” for plants that

1. Produce other plants that themselves reproduce

2. Whose “reproductive offspring” appear more than 100 meters away for seed spreaders or more than 6 meters away for root/stem spreaders

3. That accomplish the previous two items within 50 years for seed spreaders or 3 years for root/stem spreaders

The native plant enthusiast likely thinks that 100 meters in 50 years is a pretty low bar. But most introduced plants don’t clear it. It’s really unusual for a species to be able to survive, let alone reproduce, let alone create offspring that themselves can reproduce, in brand new environments. Invasion biologists study the mechanisms that allow or prevent plants from doing these things. Which is a different perspective than if an introduced plant causes harm.

An example everyone agrees on: Japanese knotweed

You may have heard of Japanese knotweed (Reynoutria japonica, or in older texts Fallopia japonica or Polygonum cuspidatum). In its native range in Japan, parts of China, and Korea, it colonizes volcanic slopes, among other habitats. It has a history of use in traditional medicine and as a foodplant in those regions, and one survey found 186 insects “associated” with it in its native range.

But if you live in one of the dozens of countries where it’s been introduced, you’d mostly hear about how destructive it is. Japanese knotweed arrived in the U.S. in the 19th century as a garden plant. It would, in theory, make a lovely privacy hedge. But like many of our worst “invaders,” it escaped and spread broadly and quickly. Where it grows, it vigorously crowds out native species and reduces habitat for wildlife, especially along waterways. It’s associated with soil eroding on the banks of rivers.

It’s also hard to get rid of. It grows 15 feet tall in a season, has thick, bamboo-like canes, and its root system is basically impossible to eradicate without herbicide. It’ll grow in sun or shade, hot or cold, drought or wet. It’s present in more than 40 U.S. states, and it’s tough to get a mortgage in the U.K. if there’s knotweed growing on the property. Every spring as it emerges, various plant subreddits fill with posts with titles like, “Is this the dreaded Japanese knotweed?”

Not all plants are Japanese knotweed

Knotweed is an obvious example of a harmful, introduced plant. It satisfies both the executive order’s definition of something that causes “economic or environmental harm” and invasion biology’s requirements for fast and broad spread.

But not every plant is an exemplar of invasion. Take the case of big leaf lupine (Lupinus polyphyllus), native to the western U.S. But it’s also on an “advisory list of invasive plants” in Maine. How can that be? Isn’t it native?

Well, it turns out that when big leaf lupine grows near sundial lupine (Lupinus perennis), the two hybridize. This is specifically an issue for the Karner blue butterfly, whose caterpillars depend on sundial lupine for food. They can’t eat the hybrid.

If this plant’s invasive, then “invasion” has a pretty broad meaning, too. You could be from another continent like knotweed, or you could be from another part of my country. And “harm” is broad. You could transform entire wetland ecosystems, or just mess with one butterfly.

How do we know if a plant is one of “the bad ones”

What I’d like as a hobbyist gardener and a native plant liker is for someone qualified to evaluate if a given plant is wrecking the neighborhood—and then to tell me, preferably in an easy-to-understand and organized way. Have they done this? Well, sort of.

Researchers score impact

To broadly generalize: invasion biologists use frameworks like EICAT to evaluate how a species affects the environment it’s been introduced to. Then they publish their results in academic journals. For example, here’s a paper that assesses Acacia species (wattles) introduced to South Africa.

Unfortunately, there are quite a few layers between an EICAT score and, for example, a typical homeowner. There’s access to the journal, the ability to understand what the researchers are saying, and the squishiness involved in assigning scores to plants. Oh, and the fact that a plant’s impact is relative to where you are doing the scoring. For example, Japanese knotweed has a tough time in the arid environment of Nevada. So its impact there is less than in, say, Connecticut.

Policymakers make lists

Government organizations publish lists of problem plants. Possibly these lists are sometimes based on researchers’ impact scores. This seems much simpler for homeowners: if plant on list, it invasive, you remove/don’t buy. If not on list, plant ok.

Seems like an accessible tool. Of course, things are always more complicated than you’d like. Most states don’t have a list; they have lists. Lists issued by different organizations within their governments. Which soometimes overlap and sometimes don’t. Let’s look at some examples.

Noxious plants

Departments concerned with agriculture typically issue lists of “noxious weeds.” According to the Bureau of Land Management, a noxious weed is a legal term for “a plant designated by a Federal, State or county government as injurious to public health, agriculture, recreation, wildlife or property (Sheley, Petroff, and Borman, 1999).” Noxious weed lists often have sidekick legal requirements that people remove said weeds from their property.

Noxious weed lists are much, much older than the 1999 executive order, by the way; Vermont passed a noxious weed law in 1795 and Pennsylvania in 1862, both dealing with Canada thistle (Cirsium arvense) among others.

Today, many states have noxious weed lists. For example:

• Nebraska Department of Agriculture

• Kansas Department of Agriculture

• Tennessee Department of Agriculture

Not all noxious plants are named at the state level. Iowa’s noxious weed law gives counties the right to legally declare a plant a problem (in addition to the state’s list).

Seed regulations

A separate but overlapping set of rules targets seeds. These are aimed at protecting consumers from purchasing seed (e.g., for crops) that contains “bad plant” seeds. There are both federal and state seed regulations in the U.S.

The noxious weed seed list sometimes, or often, differs from the noxious plant list, as in Colorado’s case.

Invasive terrestrial (grows on land) plant lists

This is a newer type of list focused on introduced plants whose presence has a major, and negative, ecological effect. New York has a list like this.

Sometimes it’s not so much a list as an “initiative.” For example, Florida’s Dept. of Agriculture maintains an official list of noxious weeds, but also makes a separate appeal to Floridians to proactively prevent plant invasions in Florida forests. There’s no official Florida list of invasive forest plants defined in state law.

Invasive aquatic (grows in water) plant lists

Various states keep lists of invasive plants that threaten waterways. For example, the Minnesota Department of Natural Resources has a list of prohibited and regulated aquatic plants.

Other examples include Maine, Indiana, and Rhode Island.

Combined lists

Some states combine one or more of these lists. For example, Massachusetts just has one list of “prohibited plants” that regulates the “sale, import, trade, purchase, distribution, propagation, [and] related activities.” Ohio similarly has a list that combines invasive aquatic and terrestrial plants (but then they have a separate, overlapping list of noxious weeds).

Being a native plant doesn’t prevent you from being “listed”

Native plant enthusiasts will frequently pipe up about how a plant can’t be invasive if it is native. That’s also what the invasion biologists say; a plant has to be introduced to be invasive.

But you can be native and be on a government-created list. For example, poison ivy, ragweed, eastern black nightshade, and sunflower (Helianthus annuus) are regulated by some counties in Minnesota in spite of being native to Minnesota. Michigan similarly regulates ragweed, poison ivy, and poison sumac, among others.

The firehose of lists is helpful (if overwhelming)

As complicated as the list situation is, they’re still reasonably useful to a concerned landowner/manager. For example, let’s consider the dandelion, a “weed” that’s known to even the most plantblind, and symbol of the wild that the perfectly manicured suburban lawn is supposed to keep at bay. Dr. Peter Del Tredici, former senior scientist at the Arnold Arboretum, once wrote about this plant,

Yank or spray all you want, the dandelion is here to stay. And while it’s considered an invasive species by some people, it is long past time to formally recognize the ubiquitous weed as a naturalized American plant.

But the dandelion’s not on my home state of Massachusetts’s prohibited plant list. Nor is it on a list in any state that borders mine: Rhode Island, Connecticut, New Hampshire, or New York. It’s certainly widespread in all of these states, but no state agency thinks it’s harmful enough to include on a list.

By contrast, Japanese knotweed’s on a list in every single state. Asian bittersweet is also on all 5 states, and so’s multiflora rose and Norway maple. Porcelain berry and burning bush are on 4 lists. So while I personally can’t make an educated judgement about how harmful a plant is, I can see that multiple state agencies—and the qualified personnel that I hope they employ—have flagged these plants. That’s a good sign that I should manage them if they show up on my property.

Getting to know who’s growing

A plant list—or even an EICAT score—isn’t useful if you don’t recognize the plant. So, to paraphrase horticultural writer Margaret Roach, it’s pretty important to get to know who’s growing near you. Where they’re from, how they spread, who eats them (and who doesn’t).

Which takes me all the way back to my argument about common blue violets. A photo, a couple of internet searches, and a few minutes could take you a long way toward getting to know this plant. It’s native across the eastern half of the United States, blooms in spring, and produces a single pretty flower. It reproduces through underground stems, creating a creeping mat. It grows in lawns and fields, but it tends to fade with heat and lack of moisture. It’s an early source of nectar for pollinators, birds eat its seeds, and its leaves are butterfly caterpillar food. It’s deer resistant and tolerates a lot of common herbicides.

It’s perfectly fine to call this plant a weed if you’re trying to grow a lawn unmarred by any species other than the specific grass you’ve chosen. But invasive? This is at least one case where the answer seems blessedly straightforward.

Plants in Plain Language is free. Subscribe to get fun and plant nerdery in your inbox.

You can also help me rationalize spending even more time on this—writing, researching, trying to get photos of very spontaneous bees—by buying me a coffee or becoming a monthly sponsor.

Let’s take a look at a single flowerhead on clustered mountain mint. No, not the silvery white leaflike things. Those are bracts, the same structures that make flowering dogwood so pretty.

The flowerheads are the half domes between the bracts. That’s where the flowers are. You’re going to need to lean in to really see these. Get your face in there. Watch out for bees, of which there will be many. But take a close look.

The flowerhead is a mortar rack with dozens of tiny flowers, which fire off one after another from about July to September. The flowers are tiny, often only a few millimeters wide. They’re white or pink and sometimes have purple spots. Zoom in with a phone or a hand lens if you have one: they look like a pair of lips (bilabiate), a typical mint family trait.

The bracts appear silvery white because a sorceress has ensorceled them to make them shimmer in the sun and intensely delightful to insects. Or it’s because they’re densely covered with fine, grayish white trichomes. Trichomes are sort of like hairs. They do important things like provide physical and chemical defenses. On this plant, they are remarkably small and dense.

The lower leaves are a darker green. They’re fuzzy, a couple inches long, widest toward the base, and opposite one another on the stem. They taper to a point and have toothed edges. They’re somewhere between an egg and a lance shape (botanists love comparing plant leaves to eggs and lances), so they’re ovate-lanceolate.

Two other features that can help identify this plant: it has the typical square stems of the mint family, and if you crush the leaves, they smell super minty.

Where it lives

Native range

Native across the eastern U.S. Its range stretches all the way to the Mississippi River, and even farther in the south (Texas, Louisiana, and parts of Arkansas and Missouri).

The range map’s a little deceptive, though. A large native range isn’t the same as “it’s ubiquitous.” Maps usually show a whole region as “within range” if a plant’s found there. But a region can be really big and only have a few plants. For example, it may be completely gone from Maine (extirpated) and endangered in a few other states. Unfortunately, it’s been a while since this plant’s status was assessed.

Habitat

In spite of its name, clustered mountain mint isn’t really a mountain plant. It lives just about everywhere there’s sun, including woodland edges, meadows, openings in forests, and even bogs. It lives in “wet, sandy, coastal habitats,” but also in “dry hills with prairie associates.” So it’s adaptable. This also makes it easier to include in various garden designs. It’d work in a cottage garden, a meadow, as a structure-providing drift, and in all sorts of soil conditions. Just make sure there’s sun.

Who it feeds and shelters

Pollinators

What do people say about plants that vigorously attract pollinators? They’re pollinator-friendly. Or more superlatively, pollinator magnets. Pollinator powerhouses. Which, ok. I feel like we’re maybe giving out participation trophies, here. Some plants are pretty good at attracting bees. And some are even better.

Clustered mountain mint is an absolute rock star pollinator plant. The Muhammad Ali of pollinator plants. It’s won multiple awards. It absolutely crushed the field in Penn State’s pollinator plant trials (2012-2014). It had 4,286 visits over the course of their trial. Second place—a goldenrod, no less!—had 923. It was also named the 2025 Perennial Plant Association Plant of the Year and the 2018 Garden Club of America Plant of the Year. I have no idea what the qualifications were for either of these awards, but the PPA says, “it’s a must have for pollinator gardens.”

So why, on a nice warm summer day, is a mature patch of clustered mountain mint veritably swarming with insects investigating its flowers?

It’s probably—this is me doing an educated editorializing—a combination of things. First, the flowers are small and clustered. It’s super easy to walk across them and access more than one at a time. This is the same reason you pub crawl on streets with a high density of pubs and not in a small town with one restaurant. Second, the flowers are open and not deceptive. Some flowers make you crawl through a tube or do various forms of insect acrobatics to get to the nectar and pollen. Sometimes you need a long tongue or a tube for a face. Not these. They’re just there waiting, like someone handing you a cold drink at the end of a long day.

Third, they’re open for a long time and during peak insect activity, summer through fall. Pycnanthemum muticum flowered for 15 weeks in the Penn State trial. Fourth, I’ve read a few sources that say that mountain mints offer unusually high nectar volumes.

Some of the above is a little speculative. For example, I couldn’t find proof behind the claim that its nectar is extra nectary. But the insect results are not. Clustered mountain mint is visited by bees, wasps, flies, moths, etc. One study, unfortunately not open access, appears to have recorded 85 species on this plant.

As a host plant

I found very little species-specific data about insects using this as a host plant. This is mainly because its foliage is full of essential oils, and herbivores don’t like how it smells or tastes. The oils are held in sacs on the trichomes on leaf surfaces. When the leaves are crushed, the oils are released, and a caterpillar gets a mouthful of gross.

There are mint family specialists, or insects that have evolved to eat plants like mountain mint without being grossed out (or poisoned) by the oils. These include the orange mint moth (Pyrausta orphisalis), the raspberry pyrausta (Pyrausta signatalis), and the hermit sphinx (Lintneria eremitus). The ranges of these 3 moths all overlap with clustered mountain mint’s, so they could potentially use it as a host.

North Carolina’s Extension lists it as a host for the wavy-lined emerald. I also found a few observations on iNaturalist of sawfly larvae using it.

Mammals don’t like it

Most mammals avoid plants in the mint family for the same reason insect herbivores do: they don’t enjoy the smell or taste of the essential oils. I’ve now read in a couple places that you can even use this plant to “guard” other plants you want to protect from browsers.

Humans are an exception, though. We very much enjoy the smell and tastes of many mint family plants, which include rosemary, thyme, sage, and of course mints and mountain mints. In fact we like them so much that we learned you could release those same oils when you heat (or cook) mint leaves, e.g., for tea. Fortunately, people tend not to go munching in your flower garden.

How it spreads

Pycnanthemum muticum spreads mainly through short rhizomes, or horizontal, underground stems. These pop up near the parent plant and produce new plants. This allows it to create dense drifts or colonies. At this point, I’m obliged to include the disclaimer, “but it’s not as aggressive as the herb mint.” (The two plants aren’t in the same genus.)

That said, native plant likers do enjoy talking about it as vigorous in the garden. Some even call it a “thug,” which I think is a ridiculous word for a plant, but it’s true that it will grow its colony, given a chance.

It’s less well known for spreading by seed. It does make seeds, of course. Its fruit is a little dry container (called a schizocarp) that splits into segments when mature. The segments are 4 nutlets, or small, dry fruits with a single seed inside.

A brief into-the-weeds: Why doesn’t this plant spread more by seed?

Here’s something weird, though. Each mountain mint produces, in theory, hundreds of seeds. And given that they grow in colonies, the colony as a whole should produce thousands of seeds. So it’s a little strange that this is only a “secondary” spreading mechanism. Apparently, the germination rate isn’t amazing.

Interestingly, trustworthy sources either disagree about how this plant’s seed spreads, or they’re painting a nuanced picture. For example, Penn State Extension says birds eat the seeds. But Maryland’s Department of Natural Resources says birds don’t like them. And North Carolina’s Extension says they’re spread by wind.

I also emailed Dr. Nicholas Ruppel, who has some experience working with this plant. (For example, one of his recent papers focused on pollinator populations in urban environments.) He told me he’s mostly noticed the plant spreading by rhizomes, though it does “jump around” the way seed spreaders do on his current project, a survey of a 43-mile long shared-use path in Virginia. He also hasn’t seen birds interacting with it.

Dr. Ruppel was careful to say that his research focused on pollinator interactions, not clustered mountain mint reproduction. And presumably the folks who write the extension webpages are, similarly, knowledgeable about plants but not focused on this one. Where this leaves us is that the picture’s fuzzy. Maybe only some birds like them. The seeds don’t fly about like milkweed or maple seeds, but they are very tiny and light—Prairie Moon nursery says there are 120,000 seeds per ounce—so the wind could certainly give them a good flick.

A couple of takeaways from this weedsy question. 1. Gardeners, expect poor germination rates. Maybe buy more seeds than you need, or get a cutting from a friend. 2. We still have a surprising amount to learn, even about relatively popular plants.

How people have used it

Records of how people used this plant are also a little sparse. Other plants in the Pycnanthemum genus, such as Virginia mountain mint (P. virginianum) and savanna or Appalachian mountain mint (P. flexuosum), have documented historical uses (e.g., for colds and fevers). But not this one.

North Carolina’s Extension says you can use the leaves and flowers for tea, and they do indeed smell quite minty when you crush them.

It’s also a bit of a favorite garden plant, especially among native plant enthusiasts. If you plant it, you will almost certainly invite insects you’ve never seen before. I don’t know if this is a selling point for folks, but I see all sorts of solitary wasps nectaring on this plant, powering up to go pest hunting.

You can even clip some for bouquets. Mt. Cuba Center reports that “the silvery appearance created by a mass planting pairs well with the lavender purple of spike gayfeather (Liatris spicata) or the rich red of Indian pink (Spigelia marilandica). It is [also] excellent for fresh or dried arrangements.”

Plants in Plain Language is free. Subscribe to get fun and plant nerdery in your inbox.

You can also help me rationalize spending even more time on this—writing, researching, trying to get photos of very spontaneous bees—by buying me a coffee or becoming a monthly sponsor.

This post is a plain language summary of a study, “Flowers respond to pollinator sound within minutes by increasing nectar sugar concentration,” by Marine Veits and 17 other authors. It was published in Ecology Letters in 2019, and is available open access through Wiley Online Library.

What researchers wanted to know

One could say that this study is about if plants can hear.

One isn’t supposed to put it that way, of course, though headlines like this one about this study did. Plants are not people. Hearing, for people, is not just a biological function. It’s shot through with other meaning, such as conversations with people you love (or hate), or maybe your favorite piece of music. Thus the standard warning for reading about research like this is, “Try not to assign human experiences to stuff that’s not human.”

Having said that, I think a little anthropomorphizing can go a long way toward making something more interesting. So let’s mix up plant and human experiences a little bit. We can call it phytopomorphizing. That is, imagine you’re a plant. One that flowers—no ferns or pine trees, please. And pick one that doesn’t blow pollen up everybody’s noses. Pick something that makes people go, “Ooh, look at that pretty flower.”

Your choice is probably among the roughly 90% of flowering plants that need animals to pollinate them. Which means you’re going to dedicate a lot of energy to attracting those animals. You might choose a specific color for your flower, maybe form it into a specific shape—one shaped like a hummingbird’s beak, perhaps. You might paint, evolutionarily speaking, a little runway for a bee that shows where the nectar is. You might even have a way to warm the air right above your flower to make a little sauna for early season pollinators (thermogenesis, but also this cool mechanism involving yeast).

All of these are sort of like a marketing campaign you spend your whole life developing to get bees and moths and flies, etc. to come visit. But when you’re done making all these colors, shapes, smells, and textures, you just have to sit there and wait. And hope. “Please, somebody notice me! I have delicious nectar! I’m very pretty!” Etc.

Wouldn’t it be cool if there was something you could do? An action you could take to get a bee’s attention? But you’re a flower. You don’t do behaviors. Right?

A group of researchers at Tel Aviv University thinks maybe you can do behaviors. They hypothesized that if plants could detect the sound of wingbeats from flying pollinators, they could actually react to them in the moment. And flowers do often look a little like those old-fashioned gramophones with the big horn sticking out. So maybe they can detect sound. Maybe they can hear.

The plant

The plant this study focused on was beach evening-primrose (Oenothera drummondii), native to Mexico and the southern U.S. (especially Texas and Louisiana). It grows on coastal dunes and other sandy areas. It blooms year round in these warm climates, a fact that I, a New Englander, find shocking.

It has the typical traits of the evening-primrose family (Onagraceae), 4 petals and 4 sepals, 8 stamens, and an X-shaped (or cruciform) stigma. It’s usually yellow, though apparently its color and shape change after it’s pollinated. Which is cool, but a story for another time.

It’s known for being pollinated by sphinx or hawk moths, a group of moths whose ability to hover while they nectar resembles that of hummingbirds.

What researchers did

If you want to learn if plants can hear, one method is to make them listen to music and see if they dance. Well, not exactly music, and not exactly listening, and not really dancing. But not not those exactly, either.

This study consisted of 3 groups of experiments.

1. Playing sounds for plants and measuring if they made sweet nectar in response.

2. Checking if flowers vibrate in response to detecting sound. Physical objects are “tuned” to respond when sound waves of the right frequency exert pressure on them. This is how eardrums work, for example.

3. Checking if a pollinator arriving predicts that more pollinators will arrive. The main reason a plant would act upon hearing a pollinator is that more pollinators are likely to show up, too. Essentially, the plant is preparing not for the one it “hears,” but for the next few minutes.

Measuring nectar

In the nectar experiments, researchers removed all the nectar from the flowers, exposed them to different “soundtracks,” and then measured how much sugar was in the new nectar the plant made. They waited 3 minutes to measure the new nectar because that’s how long it took for the plant to make enough that they could measure it. They measured it with a tool called a refractometer, which is for checking how much of something, like sugar, a liquid contains.

To understand this experiment, it’s helpful to know that a hertz (Hz) is a unit for measuring how often things repeat per second, and a kilohertz (kHz) is 1,000 Hz. Lots of hertz gives you something higher pitched, and fewer hertz gives you something lower pitched. For example, a flute is between 261 Hz and 2.1 kHz, and a tuba’s between 41 and 262 Hz.

Here are the soundtracks they tested:

1. Silence, as a control for the experiment (or perhaps because they’re big John Cage fans).

2. “Bee.” This was a recording of a honey bee from 10 centimeters away (i.e. hovering above a flower).

3. “Low,” a 10-second track that ranged from 50 to 1000 Hz, which apparently is the range most pollinators’ wings beat in.

4. “Intermediate,” a 10-second track that ranged from 34 to 35 kHz, which is about the range of a dog whistle (and inaudible to humans).

5. “High,” a 10-second track ranging from 158 to 160 kHz. This is super high frequency, like in the range that bats need for echolocation. It served as a second control, helping them check if flowers responded to the speaker’s electromagnetic fields. (All electrically charged objects generate electromagnetic fields.) The assumption is that this is such a high frequency track that it’s basically silence plus an electromagnetic field.

They played these tracks across 4 nectar measuring experiments, each with a different flavor of design. It’s not clear what question each experiment was designed to anwer.

Measuring if hearing one pollinator predicts others arriving

The nectar experiments measured if plants responded within 3 minutes of detecting sound. But 3 minutes is kind of a long time. A bee that appears right now is unlikely to be there 3 minutes later. Unless it’s taking a nap, which bees sometimes do on flowers. But that’s unrelated to this paper.

So what’s the point of making new, sweeter nectar if the pollinator you heard is already gone by the time you make it? One possibility is that pollinators come in clusters. Honeybees and bumblebees, for example, are known to forage in groups. Honeybees even do a form of interpretive dance to tell their buddies where the food is.

To make sure that pollinators visit in groups, researchers filmed a bunch of flowers at dusk and checked if one pollinator arriving meant another one would come soon after. I’d like to report that they watched these films with a bowl of popcorn in one hand and a stopwatch in the other, but the reality was much more technical and careful.

Measuring petal vibration

Researchers used something called laser vibrometry to measure if petals moved in response to a soundtrack. This involves measuring the shift in a laser beam caused by a vibrating surface. Sorcery, more or less.

There’s less detail about the “soundtracks” for these vibration experiments, which were different than in the nectar measuring experiments. They were:

1. Silence

2. A recording of a bee

3. A recording of a moth

4. “Low” (1,000 Hz)

5. “Intermediate” (35 kHz)

6. “High” (160 kHz)

7. A live bee held by tweezers several centimeters from the flower! (exclamation mine)

Though the paper refers to multiple vibration experiments, it doesn’t say what was different about each.

What researchers found

More sugary nectar

Beach evening-primrose flowers produced about 20% more sugary nectar 3 minutes after they “heard” the bee soundtrack and the “low” soundtrack (the one with the range that pollinators’ wings beat in). Previous research suggested that bees can tell the difference when the sugar increase is as small as 1-3%, apparently, so this is a big boost.

These results didn’t change regardless of growing conditions, e.g. grown indoors vs. outdoors, different seasons etc. Flowers didn’t produce more sugar when they heard the “intermediate,” “high,” or “silence” soundtracks.

A pollinator arriving predicts more pollinators arriving

As a reminder, “3 minutes” comes from how long it took for the flowers to get enough nectar for them to measure sugar concentration. It doesn’t actually tell us the exact speed of nectar refilling, or when a pollinator would begin to notice it. But it is fast—fast enough for the next pollinator who arrives.

And pollinators do cluster their visits. Researchers found that pollinators are much more likely to show up if another pollinator had been there within 6 minutes. This means that it’s probably worthwhile for plants to up the sugar in their nectar on hearing a wingbeat, since another bee or moth is likely on the way.

Flowers are kind of like ears

Researchers found that the flowers vibrated in response to the bee recording, moth recording, and the bee held (gently, one hopes) by tweezers. The vibration experiment also showed that flowers vibrated more when they had more petals. Removing petals decreased the vibrations. This suggests it’s the petals that are doing the “listening.”

So in sum, the flowers seem “tuned” to the frequencies of pollinators’ wings. This could help them filter out, for example, wind frequencies, which are lower.

Why it matters

It’s…cool

First things first: this study shows plants responding in the moment and quickly to sound. That seems fundamentally different from evolving a flower with a specific color or shape. It’s a behavior. I don’t know about you, but I think about behaviors as things animals do, not plants.

Also, the fact that the flower itself is functioning as an ear is startling. We think of flowers as things we look at and smell, not as organs that are constantly eavesdropping on the world. (“Is there a bee around now? How about now? What about now?”)

It’s about sex, like always

It seems like quite a lot that we learn about flowers comes down to, “That’s a thing that helps them reproduce.” This is no exception, but it is a totally new type of “thing.”

There are two components of the new thing. One is that plants can hear pollinators. The other is that they can respond by sweetening their nectar. This is cleverer than it might seem. It’s probably obvious that sweeter nectar might attract pollinators. But if that’s true, why not just have sweeter nectar all the time?

Because producing sweeter nectar can be expensive. And nectar that’s just sitting there waiting can be eaten by microbes and “robbers.” Nectar robbing is an actual technical term where insects that don’t pollinate plants show up and drink their nectar. Sometimes they even bite a hole in the bottom of the flower to get at it.

You don’t want to attract nectar robbers if you’re a plant. You want to attract something that will contribute to reproduction. And so you reserve the good whiskey for when your real friends come over. Or you only take the little blue pill at the opportune moment. Or…

…perhaps that’s enough comparisons. The point is that it’s advantageous for plants to wait to sweeten their nectar until the right moment. Being able to “hear” lets them do that.

A new field of study

This paper claims that it’s “the first step in a new field,” phytoacoustics. I’m not sure if it was the first, but it certainly was a landmark. Other studies that have helped establish this new field include a 2017 paper that found that plants were able to use vibrations, or “acoustic cues” to find water, and a 2025 paper that asked if “windmill-like” noise affected pea plants’ growth as well as the insects that feed on them.

There was also a 2023 study that suggests that plants actually make sound when they’re stressed (at a frequency people can’t hear). Which is also very cool. One could say this means that not only can plants listen to music, they can play it, too.

Well, not exactly music, and not exactly play. But not not those exactly, either.

Plants in Plain Language is free. Subscribe to get fun and plant nerdery in your inbox.

You can also help me rationalize spending even more time on this—writing, researching, trying to get photos of very spontaneous bees—by buying me a coffee or becoming a monthly sponsor.

Squash plants are monoecious: they have separate male and female flowers on the same plant. Only the female flowers produce squash, though they need pollen from male flowers to get started. Usually, bees do the work of transferring the pollen from male to female flowers.

What’s a squash?

When we say we’re growing squash, we mean something in the Cucurbita genus, such as summer squash, acorn squash, and pumpkins. A zucchini, by the way, is a type of summer squash. And summer squash is more of a culinary category than a botanical one—but culinary and botanical vocabularies tend to get mashed together in the vegetable garden.

You might also grow cucumbers or melons, many of which are also monoecious. Confusingly, honeydew and cantaloupe are in the same genus as cucumbers, Cucumis, but watermelon is part of the genus Citrullus. All of these are in the gourd family (Cucurbitaceae), one of whose common features are separate male and female flowers.

How to tell male and female squash flowers apart

Female squash flowers have what looks like a miniature version of their fruit at their base. Sort of a sneak preview of what they’re going to make. This is technically an ovary, and becomes a fruit once it’s fertilized. Males don’t have an ovary at the bottom, just a narrow stem, or peduncle, that attaches to the rest of the plant.

While researching for this post, I encountered more than a few sources claiming that female flowers tend to grow in the center of the plant. I assume this claim is based on the idea that some squash grow as bush-style plants, and males’ long peduncles make them appear farther away from the plant’s “center” than female flowers.

But I wouldn’t recommend paying much attention to this. For one, lots of squash grow as vines, and those produce flowers along the vine. For another, even if there are flowers at a plant’s “center,” you still have to look for the ovary at the flower’s base to figure out if it’s male or female.

Too many male flowers?

I’ve heard gardeners worry that their plants are only producing male flowers. One reason for this might be that there just tend to be more male flowers than female flowers on most plants, and this is even more pronounced early in the season.

I wrote to Dr. Susan Chan, who’s studied and written about squash pollination, to ask about this. She pointed out that it takes a lot more energy and resources for plants to make female flowers, which come with ovaries and various other female flower features. Starting with male flowers is the less expensive way to attract bees. Dr. Chan has also written elsewhere that bees will often return to a plant as long as it offers pollen and nectar. So if you were a squash plant, you’d want to get your advertisements posted as early as possible.

Not all cucumber genus plants have male and female flowers

As I mentioned above, some Cucumis varieties don’t follow the pattern of separate male and female flowers on the same plant. For example, many types of American cantaloupe have both male and perfect flowers on the same plant. A perfect flower has both male and female parts. This doesn’t change much for the Gardener Who Wants To Grow A Melon. These plants still make male-only flowers early, perfect flowers later, and need bees to move pollen from here to there. (Apparently, some types of watermelon can have perfect flowers, too, but we don’t usually grow those.)

Some varieties of cucumber can also produce fruit without being pollinated at all, such as the Adam Gherkin and Sweet Success varieties. You may see these listed as parthenocarpic. If you’re growing those, you don’t need to think about bees or which flowers have which parts at all. Though I recommend at least thinking about bees. They’re fuzzy.

How pollination works (and how it leads to fruit you get to harvest)

Squash flowers last less than a day. “Youth’s a stuff will not endure,” etc. Both male and female flowers open in the morning. Some species’ blossoms close up shop as early as midday.

Cucumbers tend to stay open a little longer, but I’m not aware of any that are long-lasting. (I think a shop is probably the best metaphor here. There’s an obvious alternative, but I send these newsletters at 6 a.m.)

What this means is that there’s a brief period when the shop’s open. During this time, we’re hoping that bees land in the male flowers, get covered in pollen grains, and carry them to female flowers. There, the grains germinate and grow tubes down into the ovary, and we’re off to the make-a-fruit races.

Fruit, by the way, is a botanical term for the structure that carries seeds. There’s no such thing, botanically speaking, as a vegetable. But once again, we’re in the vegetable garden where the culinary and the botanical are mashed together like a casserole, so don’t let anyone lecture you about that. And “vegetable” is a category of things we eat. So zucchini is, linguistically, both a fruit and a vegetable. Take that, pedants. Alternatively, you could out-pedant them and say, “Well actually, it’s a pepo, or a fruit with a hardened rind.”

Bees pollinate squash, and you should invite them to your vegetable patch

The most obvious bees to mention in connection with squash pollination are squash bees, a name that covers about twenty species. These ground-nesting, solitary bees specialize on pollen produced by plants in the Cucurbita genus. Most live in warmer climates. For example, I’m likely to encounter only one squash bee species here in New England, the pruinose squash bee (Xenoglossa pruinosa, though you’ll also see it labeled with its older Latin name, Peponapis pruinosa).

Depending on where you live, your other frequent collaborators will likely bee (sorry) bumblebees and honeybees. And I’ve seen the occasional sweat bee poking about.

It’s worth considering if bees want to visit what you’re growing. For example, perhaps you’ve got squash bugs and are spraying insecticides. Bees are also insects. Not a good customer experience. Similarly, if you’re treating your yard or plants near your vegetable garden, your squash plants could receive some pesticide drift.

If you’ve got a small backyard vegetable garden, you can add flowers on the edges, which will make the planting generally more interesting for bees.

You can also hand pollinate your squash. I’ve never bothered with this, though it seems like it could be fun. Here’s a hand pollination guide from West Virginia University Extension.

A coda: Harvesting squash flowers

If you’re going to have excess male flowers, and they’re not going to produce fruit, and they’ll be gone tomorrow, you may as well harvest a few and eat them. People typically stuff them with ricotta and herbs and fry them.

Harvest in the morning; later in the day, the blossoms may already be starting to go limp.

Also, check to see if there are insects inside before you harvest. Bees get to work early, and ants are pretty equal-opportunity nectar thieves. Dr. Chan writes that “Male squash bees spend the afternoon and night sleeping in the wilted, closed Cucurbita flowers.” Which is both adorable and a good reason to make sure you look before you pick.

Plants in Plain Language is free. Subscribe to get fun and plant nerdery in your inbox.

You can also help me rationalize spending even more time on this—writing, researching, trying to get photos of very spontaneous bees—by buying me a coffee or becoming a monthly sponsor.

At the top are bright red tubes. Each of these is an individual flower, its petals fused and rolled. Flowerheads can contain at least a couple dozen flowers, and many more in cultivated varieties. (There’s probably a tradeoff. For example, Monarda “Cotton Candy” supposedly contains 280 flowers on its flowerheads, but one wonders how much nectar or pollen the plant has to sacrifice to make all these.)

The flowers don’t bloom all at once. They start in the center and work outward over time, sort of like a blastwave in an action movie. What’s great about this is that it means the overall bloom time is long, from June through August, and longer in cooler climates.

Like other mint family flowers, the tubes look like they end with a pair of lips (they’re bilabiate). The stamens and styles poke out the top, and the tubes seem to stick out chaotically. The effect is something like a muppet that’s fallen on hard times.

It’s not actually chaos, though. This plant has flower structures called verticillasters. This is a structure where two arcs of flowers come together in what appears to be a ring. And in this species, they’re basically completely mashed together in the flower head. Hence the messy haircut look.

Beneath the scarlet petals are reddish and green sepals, which protect and support the flower. Beneath those are reddish, leaflike bracts, which have a similar job. In scarlet bee balm, bracts also make the whole red flowerhead bigger and easier to see. Go go gadget hummingbird billboard, etc.

Leaves and stems

Monarda didyma has the mint family traits of square stems and leaves opposite one another on the stem. If you crush the leaves, they smell minty. The leaves are dark green—darker and larger, in my experience, than wild bergamot’s (Monarda fistulosa). Little teeth run all along their edges. They’re somewhere between egg- and lance-shaped (ovate and lanceolate).

Scarlet bee balm also doesn’t have any basal foliage, or the foliage that appears in a ring around the soil. It just sends its stems vigorously upward. All its leaves are on its stems (cauline).

Illinois wildflowers observes that in hot weather, the lower leaves can fall off (especially if the plant is also struggling with powdery mildew). This isn’t the end of the world, though it does tell us that this plant that prefers slightly cooler temperatures and some moisture in the soil.

Powdery mildew

Many popular Monarda species, including this one, are infamous for getting powdery mildew. Powdery mildew’s a fungus that creates a white, powdery film over the plants’ leaves. Monarda like to grow in tight drifts, contributing to the kind of humid, moist conditions that powdery mildew likes.

Powdery mildew is mostly cosmetic damage. It doesn’t stop the plant from reproducing. But it’s not amazing to look at. Supposedly you can slow it down a bit by dividing clumps so there’s more airflow, clearing infected leaves, or using mildew-resistant varieties such as Jacob Cline.

Where it lives

Habitat

Grows in the moist understory of mountain forests up to 6500 feet, especially where there’s an opening that allows in a little more sun. The cooler temperatures and extra water in the forest understory probably protect it in the southern part of its range. It doesn’t love dry soil or being blasted with sun.

Flora of The Southeastern U.S. mentions that it appears wetlands, along streams and waterways, and in seepage slopes, or hillsides where groundwater keeps the soil continually wet.

Native range

Scarlet bee balm’s native range might originally have tracked the Appalachian mountains from Alabama and Georgia through Maine. The range then continues up in a narrow strip through New Brunswick in Canada.

The plant’s range has expanded probably in part because the horticultural industry sells it. It’s now found east to the Atlantic coast and west as far as Minnesota.

A wonky acknowledgement: Because this plant’s range has expanded so much, you might read “expanded” as meaning, “the horticulture industry and its customers brought this plant to new places, and we don’t know what it means for the ecosystems it’s now a part of.” To which someone might respond, “but the new place is geographically right next to the old place. A lot of the things that depended on it in the old places also live in the new places.” And the debate could continue from there—but not in this post.

Who it feeds and shelters

Pollinators

This is one of those plants that appears on lists of hummingbird favorites, and with good reason.

The flower tube’s shape makes it seem almost like a little sock for a hummingbird beak, and Monarda didyma is especially associated with the ruby-throated hummingbird. As an aside, there’s been some debate about if red really is associated with birds. A 2025 paper in Current Biology makes a very convincing case that they are. The authors show that red and orange flowers in North America bloom in time for the arrival of migrating hummingbirds.

Anyway, whenever someone mentions that something’s a hummingbird plant, a good bet is that it’s also a butterfly plant. Many butterflies have an organ called a proboscis, or tube-like feeding structure, sort of like you had a straw for a mouth. Or in this case, as if you had a hummingbird beak for a mouth. This allows them to reach the nectar in scarlet bee balm’s tubes.

Some bees will nectar on scarlet bee balm, too, especially if they’re a long-tongued variety (like many bumblebees). I assume they still have to crawl part way down the tube to get at the nectar, resulting in one of those extremely cute Protruding Bee Butt situations.

As a host and food plant

A few bees specialize on pollen produced by plants in the Monarda genus, though I’d imagine they prefer spotted bee balm or wild bergamot, since those plants’ pollen is more accessible. These bees include the beebalm shortface bee (Dufourea monardae) and the delightfully-named Bee Balm Fairy Bee (Perdita gerhardi). Another cited species, Protandrena abdominalis, is some type of rare mining bee that I found very little info about. For what it’s worth, none of the iNaturalist observations I saw of these bees were on M. didyma.

A few different caterpillars use this plant as a host. One, the hermit sphinx caterpillar (Lintneria eremitus) looks like it crawled out of the Upside Down in Stranger Things. Others include the gray marvel (Agriopodes teratophora), and a couple of pretty moths, the orange mint moth (Pyrausta orphisalis) and the raspberry pyrausta (Pyrausta signatalis).

The HOSTS dataset includes 4 records of species using scarlet bee balm and 20 across the Monarda genus. (Some of these may also eat M. didyma, but HOSTS is a record of literature mentioning relationships between caterpillars and plants, and that literature may not have focused on scarlet bee balm.) Interestingly, neither the hermit sphinx nor orange mint moth is included here—a hint at the limits of our knowledge.

In case you’re wondering (because I was) if powdery mildew makes this plant taste worse to caterpillars: maybe not? I found one study that said that caterpillars on field mustards didn’t care about powdery mildew, though their wasp predators did.

This plant’s valuable for wildlife after it’s finished blooming, too. Small, overwintering songbirds will eat the seeds, including American goldfinches and song sparrows.

Some solitary bees will also nest in the stems over the winter. In general, they do this by finding a hollow or pithy stem and creating a nest cavity. Carpenter bees will chew through pith to make a nest, and others have to find a stem that’s already hollow. Similarly, some can tunnel into a flower with the head on, and some need a stem that’s already open.

The standard advice for creating bee habitat is to cut back to 1 or 2 feet in the fall. However, cutting the stem does dump the seedheads that the birds like. So you could cut the stems and leave the seed heads on the ground for the winter. If this looks too messy, you could gather the seed heads and neatly pile them or put them in an out-of-the-way spot so that birds can still get them.

How it spreads

Runners

Scarlet bee balm spreads through two types of runners. It sends out rhizomes, or underground stems that travel horizontally and poke up new shoots, like mint plants (the herb). And it also has stolons, or aboveground horizontal stems. (Strawberries and clover are also other plants you might’ve seen spread by stolons.) Both rhizomes and stolons form clones of the original plant.

When it spreads this way, it forms drifts and colonies, and can do so vigorously. It has a bit of a reputation as an “aggressive” garden plant. On the other hand, it’s nice that it creates fairly large drifts quickly. You can cut the drift into a nice, even shape every so often.

What I’d avoid is planting it next to slower growing, clump-forming, shorter plants. It’d certainly be happy to encroach on and overtake a newly planted hosta (if you’re into those) or peony. Even some taller plants, like purple coneflower, may need you to tell the bee balm (i.e. with your clippers) to back off. Missouri Botanical Garden recommends dividing every few years.

Seeds

Monarda didyma also spreads by seeds. This accomplishes two things. First, genetic diversity: they’re not clones of the parent plant. Second, it allows it to reach sites beyond its current drift or colony.

After the flowers have been pollinated, they form little containers with 4 nutlets, or small, dry fruits with a single seed inside. Since each tube is a flower, each creates its own container of nutlets. These may drop or be carried by birds to new locations.

If you’re growing it: most guides I checked said that it’ll germinate whenever you sow it. A few others said cold treatment helps (i.e. simulating winter). If you’re not in a rush, I’d do the cold treatment; your germination rate will likely be a lot better.

Don’t bury the seeds. They need sunlight to grow; just scatter them on the surface.

How people have used it

Scarlet bee balm’s leaves are edible, and taste a little like minty oregano. One of its uses among indigenous people was, not surprisingly, to make tea. The common name Oswego tea probably refers to Oswego, New York, which is where colonists may have learned about the plant from the local people, who were members of the Haudenosaunee (or Iroquois) confederacy.

The book Cherokee Plants and Their Uses—A 400 Year History (Paul Hamel and Mary Chiltoskey) also lists a few ways the Cherokee used this plant medicinally. These included to treat colds and to cause sweating (as a diaphoretic). The Cherokee’s original land occupied a good chunk of the southern Appalachian mountains, overlapping this plant’s native range.

Today, we use this plant a lot in gardens, both for its ecological benefits and because it’s pretty. The International Registrar of Monarda cultivars lists 83 Monarda didyma varieties as of 2024, including hybrids. This tells us there’s a bit of a market for this plant.

Which is nice. One loves to see a native plant make it to the horticultural big leagues, as it were. A warning here, though: some nurseries or growers will treat plants with pesticides so they’ll appear “fresher” on the shelf. If you’re planting it to support wildlife, this is counterproductive. You’d want to buy from a trusted source, or at least be the annoying customer at the unknown source who wants to know where a plant came from and if it’s been treated with something.

Plants in Plain Language is free. Subscribe to get fun and plant nerdery in your inbox.

You can also help me rationalize spending even more time on this—writing, researching, trying to get photos of very spontaneous bees—by buying me a coffee or becoming a monthly sponsor.

If the person’s vaguely interested, I might also offer that native plants have important roles in our ecosystems, that birds need the food and habitat they provide, or that some bees have evolved to only use the pollen of specific native plants.

One must be a little cautious with one’s unsuspecting conversation partners. Because native plant talk has a whiff of advocacy. Not just any plants, native ones. They’re what you should plant. Not those other plants. Advocacy when you’re not expecting it can be grating. And I assume that most people in casual conversation about their gardens are not expecting it.

Sometimes, at nurseries, I see someone pick up some lovely-looking seedling, admire it. I see myself racing toward them, hurdling shrubs, upsetting the annuals tables, shouting desperately to the consternation of other shoppers, “No! Not that one! It’s from the other side of the world and it colonizes woodlands to the detriment of our native groundcovers!”

I suppress the impulse, but it’s there. At least my heart’s in the right place.

Plant-eating insects need the plants they evolved to eat

The crux of native plant advocacy is that native plants support more local wildlife than nonnative plants do. The entomologist Doug Tallamy is probably most responsible for popularizing this notion. For example, in Bringing Nature Home (2007), he describes this ecological “cascade”:

1. Plants “eat” sunlight

2. Caterpillars and other insect herbivores eat plants

3. Birds feed caterpillars to their young

Now, none of the living things in this cascade want to be eaten. Plants, for example, defend themselves chemically. To eat them, you need to evolve a way to deal with those chemicals. So insect herbivores are less likely to eat plants they didn’t evolve with.

For example, the Norway maple, one of the most popular trees to plant in the U.S., supports maybe a dozen types of caterpillar. By contrast, our native red maple supports more than 100. Norway maples are, as the name suggests, a European species.

Caterpillars are not the only beneficiaries of native plants. There are specialist bees that need the pollen of a few native plants (or just one). There are also gall wasp larvae, sawfly larvae, beetles, and aphids that rely on the plants they evolved with.

Most people I speak with aren’t super enthusiastic about aphids or anything involving the word “larvae.” This is probably why native plant enthusiasts, including Tallamy, focus on the more charismatic beneficiaries of native plants.

The frequently cited example: Carolina chickadees

Probably the most popular example of “why native plants” is the Carolina chickadee. These birds feed their young caterpillars, spiders, and other soft-bodied insects. And they do it a lot. The oft-repeated number is that it takes 6,000-9,000 caterpillars to raise a clutch of Carolina chickadees. (More on this range later.)

So you can’t raise chickadees without a lot of insect biomass around. And native plants are, leaf for leaf, better producers of insect biomass than non-native plants. They make more caterpillars, spiders, and soft-bodied insects available for chickadee chicks.

Geography helps people pick plants that wildlife are more likely to eat

So far I’ve written a lot about things eating and getting eaten. But “native” and “nonnative” seem more like labels for “it’s from here” and “it’s not from here.” Are we talking about ecosystems or where plants live?

The answer’s both. Obviously, plants don’t care about state or country boundaries, and neither do the things that eat them. But geography’s a good proxy for “evolved alongside local wildlife.” Black cherry (Prunus serotina) is an important tree for many plant-eating insects near me. I don’t need to know what they all are. Which is good, because it’s surprisingly hard to get an answer to the question, “Name all the bugs that eat this tree.”

Real nerds will use something called an ecoregions map to learn where plants evolved. An ecoregion’s a region where the conditions are fairly similar. You can do this on a large scale, like “eastern temperate forest,” which covers the easternmost third of the U.S. Or you can look at a much smaller region, such as the “coast range,” which covers a narrow strip of the U.S. west coast. (These are called level 1 and level 3 ecoregions respectively.)

The science underpinning native plant gardening

The science behind native plant gardening is relatively new. It’s built on much older ideas, such as that insects evolved to overcome plants’ chemical defenses and that baby birds eat a lot of insects. But the specific body of research that powers today’s native plant advocacy is fairly recent.

A good chunk of native plant gardening talk has been generated by Tallamy and by people who studied or worked with him at the University of Delaware. These latter include Desirée Narango, Karin Burghardt, Adam Mitchell, Kimberley Shropshire, and Emily Baisden. The papers they authored, many with Tallamy as a contributing author, are more or less the foundation for native plant gardening today.

For example, Burghardt’s 2009 paper, one of my first encounters with this research, found that caterpillars (and birds) were much more common on native plants than nonnative plants. Narango’s research has found that the “abundance of both caterpillars and spiders declined as nonnative plant biomass increased” and that “curbing the spread and use of non-native plants” helps prevent insect populations from falling. Another of Tallamy’s students, Ashley C. Kennedy, conducted research on the importance of caterpillars for nesting bluebirds.

Other pockets of researchers beyond Tallamy and his collaborators have also emerged. For example, there’s Annie White’s dissertation on natives vs. cultivars (plants we’ve bred or selected to look a certain way), and the trial gardens at the Mt. Cuba Center. I wrote about their goldenrod trial a few weeks ago.

This work is less diverse than we’d like. It’s mostly conducted in the U.S. mid-Atlantic and northeast by a small, mostly-interconnected group of people. This isn’t sinister; it’s how academia works. You dedicate your life to researching something, and therefore others who are interested tend to seek you out.

But as a consumer of this research, I do wish there was more argument and disagreement. That’s how tires get kicked and knowledge made.

Where there’s nuance

A 2015 Royal Horticultural Society (RHS) paper tested if there was a difference in insects “associating” with native and non-native plants in the U.K. They found that flowers provided resources for pollinators “regardless of the plants’ origin,” that “natives and near-natives” drew the most pollinators, and that exotic plants could “extend the flowering season.”

This paper focused on pollinators, not caterpillars. It also took place in another country. Those differences are good, even critical for what we know. And their results suggest, “Actually, exotics do have a place in the garden.”

Another example: a paper about coral vine (Antigonon leptopus) invading a Caribbean island ecosystem found that insect populations didn’t fall where the vine invaded, but they did change. They became “nearly indistinguishable” wherever the vine took over. This means some species suffered while the ones that happened to be well adapted to the vine thrived. This is a result that says nonnatives reduce insect diversity, not insect counts.

And finally, let’s return to the 6,000-9,000 caterpillars needed for a Carolina chickadee brood. This range number, which Tallamy cites in a 2021 paper, is based on a 1961 study by Richard Brewer. Brewer observed Carolina chickadees feeding their young about 2.6 times per hour for each chick. This 6,000-9,000 range is cited all over the place. (Google the phrase 6,000-9,000 insects.) And yet if you do the math using Tallamy’s constraints (16-18 days of feeding, feeding from 6 a.m.-8 p.m., 6-8 chicks per nest), the range should be 3,600-4,800 per brood.

This doesn’t change the main argument. Carolina chickadees feed their young a lot of insects, and native plants make this possible. But it’s a little scary how many places simply cite 6,000-9,000.

This is the uneven ground where advocacy adopts scientific findings. It’s also one reason we should root for more research and more perspectives. Currently, a few outsized studies and people dominate the landscape and tend to dictate the “conversation.”

Where there’s critique

The most forceful, or at least most cited, critique of native plant enthusiasm comes from Arthur Shapiro, a specialist in butterflies and moths at University of California, Davis. In 2003, he co-authored a paper that found that 34% of butterfly species used nonnative plants as host plants. He argued that ecosystems are more adaptable than native plant enthusiasts give them credit for.

It’s important that Shapiro did his research in California, a landscape highly modified by agriculture, and very different from Tallamy’s context in Delaware. This is the kind of opinion diversity that native plant discussions need. They push conversations forward. For example, Tallamy has responded to this, saying that Shapiro’s examples demonstrate host-range expansion, not host switching. Most insects, he argues, need to evolve, which takes time.

Another common critique of native plants is that “native” and “nonnative” are arbitrary categories, and the world is not so black and white. Peter Del Tredici, former senior scientist at the Arnold Arboretum, articulates a good version of this argument. He proposes that

any plant that can be documented as growing spontaneously in North America prior to 1800 should be considered a naturalized “American archaeophyte” with all the rights and privileges associated with being native.

It’s time for “amnesty” for the dandelion: while it’s “considered an invasive species by some people,” we should acknowledge that it’s been here in the U.S. for hundreds of years.

One last critique comes from people who, I suspect, conflate the often xenophobic politics of immigration with the language of “nonnative” and “invading” plants. If a plant’s here, this argument says, it must deserve to be here. It’s “natural.”

But the majority of nonnative plants didn’t choose to come here. They were brought here, usually by people in the horticulture industry, or perhaps by colonists, and often for ornamental or agricultural purposes. So if you take this position, you should at least wrestle with the idea that people moving plants around the world is fundamentally different from evolution doing it. (And yes, people are animals, but which other animal has a horticultural industry?)

Debates about native plants seem focused on the margin

Having acknowledged that nuance and critiques exist, I’d now like to do some eye rolling. As we’ve established, native plants are part of a larger conversation around preserving ecosystems. The major challenges within that conversation aren’t really the subject of argument. They’re also broader than just “plant native plants.”

For example, nobody’s scrunching a brow about if white oaks are native all along the U.S. east coast (they are). Or if goldenrods support a tremendous number of insects (they do), or if wild strawberry (Fragaria virginiana) is an ecologically beneficial groundcover across most of the U.S. (it is).

But this is not what the critiques of native plants tend to focus on. People like to say, “What’s the threshold for how long you have to ‘evolve’ with wildlife to be ‘native’?” Or “what counts as ‘local wildlife’?”

There’s a time and place for such questions. It’s called graduate school. But they’re questions about the edges, not the really important stuff at the center. The conversations I have with my neighbors in the suburbs are about things like spraying for mosquitoes and not raking away all the leaves. Maybe I get the chance to recommend—or on a really good day, give away—a plant.

Native plant gardening is also about small-scale land management

With respect to Dr. Del Tradici’s dandelions: no native plant gardener I’ve met cares much about dandelions. The real dandelion haters are the lawn fetishists. Native plant enthusiasts are a lot more irritated by lawn fetishists than dandelions.

Which points to something funny. Native plant enthusiasts tend to talk about a lot of things other than just native plants. We might group these issues together under a banner like “suburban land management,” which is perhaps less interesting than “native plants.” They include things like reducing the size of your lawn, not spraying for mosquitoes, and not raking away all the leaves. It makes sense that native plant enthusiasts care about these issues. They, like choosing native plants, are a reaction to typical suburban landscaping practices. Tallamy’s books are full of suggestions like, "turn off lights at night” and “reduce the use of pesticides.”

This is one obvious reason there’s potential, sometimes explicit, conflict when native plant lovers talk about native plants. The native plant lover thinks many typical suburban gardening practices are bad. The implication of my definition of a native plant—things local wildlife need—is that choosing a nonnative when you could choose a native is a missed opportunity. Thus these conversations include an element of judginess, of “you did it wrong.”

Of course, native plant gardeners are also gardeners. We enjoy zinnias and strawflowers and cosmos. We’ve probably put in a hosta or two. Most of us know that replacing an entire lawn in one single project is a recipe for overwhelm. And we love talking about the plants we love. We usually try to be practical about The Work.

Native plant gardening in the suburban neighborhood

Most of my neighbors don’t spend a lot of time thinking about supporting insects and birds. (And I don’t likely spend as much time as they’d like thinking about the subjects they care about and advocate for. There’s only so much time in the day.) These folks might dedicate the minimum possible energy to their outdoor spaces, just enough to “fit in” with the culture of their neighborhood. Perhaps they pick out something pretty on a whim at the hardware store every so often.

This type of person, I think, changes when the plant inventory at Home Depot changes, or when their neighbors’ yards change. The “native plant conversation” with this person might be that they compliment some little meadow area I have when they walk by with their dog. “Do you want one of the yellow ones?” I say. “Bees love them!” That’s a highly successful “native plant conversation.”

Is this sad? Perhaps a little. It’s always a little sad to learn that the person you’re speaking to is less enthusiastic than you about something you care about. But it does help set expectations about what a reasonable level of enthusiasm, interest, and action might look like.

I recently had a neighbor tell me he wants to remove “all that stuff at the back of the yard that’s an eyesore.” He was talking about a stand of mugwort (eastern Asia and north Africa, listed as invasive in several states) that crosses our properties. Of course I want to help with this. I’ll even suggest a few native replacements that are a little easier to manage, that don’t look like “an eyesore.” I don’t need to mention ecoregions at all—if I can help myself.

At least my heart’s in the right place.

Butterfly weed is a short, clumping milkweed that grows to two or three feet tall. It has stems covered in soft, fine hairs.

The leaves are narrow, lance-shaped, with pointed tips. The edges are smooth, no teeth or indentations. They look a little like rosemary leaves (the herb) that’ve been working out. The leaves spiral and alternate (they’re not directly across from each other) up the stem. It’s not super easy to see this, though, because they crowd together chaotically. (See Flora of North America and Illinois Wildflowers for more technical descriptions.)

But let’s get to what you really want to know about: the flowers. Plants in the Asclepias genus have some genuinely unusual flowers, and butterfly weed’s no exception. Describing them involves some brand new jargon, but it’ll be worth it. You’ll never look at butterfly weed, or any milkweed, the same way again.

In this species, the flowers are tiny, and usually bright orange, though someone can turn the color slider toward yellow or red. They flowers are displayed in a slightly domed umbel. An umbel is a cluster of flowers that’s built like an umbrella, with a flat-ish top and many stalks connected to a central point. Each butterfly weed umbel might have one or two dozen flowers on it.

If you look more closely, you’ll notice that each individual flower is a tiny, miniature knockout. Each has five petals that bend back sharply toward the stem (they’re reflexed), sort of like it’s wearing a ball gown. Pointing directly upward is a crown of hoods. Each of these contains a horn, which looks like a tiny (2 millimeter) tongue trying to touch the top of a mouth. The hood is where the nectar is, and the horn’s purpose is probably to guide pollinators to the nectar.

At the base of the hood and horn structure are the reproductive bits, which in milkweeds are fused together. This is called a gynostegium. The pollen is stored here, though it’s not loose like in other plants. It’s kept in little waxy sacs called pollinia. Each flower usually makes 10 of these sacs.

The clearest image I found showing milkweed flower anatomy was in an iNaturalist journal. The author uses Zizotes Milkweed or Side-cluster Milkweed (Asclepias oenotheroides), not butterfly milkweed, but the parts and locations are the same.

The U.S. Department of Agriculture also has a useful guide to milkweed pollination and flower structure that provides much more depth on the anatomy.

Milkweed pods

After they’re pollinated, milkweed flowers turn into pods. Technically, these are follicles, dry pods that split open along a single seam. Butterfly milkweed pods are slender and long. Inside are seeds, each of which has a tuft of silky, flosslike hair attached to one end, like a comet or a Dr. Seuss character. These fibers help lift them into the breeze, and they also repel water. Birds sometimes use them to line their nests.

Where it lives

Habitat

Butterfly milkweed is a plant that reminds us that “poor soil” is a human-centric way of looking at things. It doesn’t want rich, moist soil. It likes sandy, rocky soils. It’s found in dry fields and near railroad tracks and roads. It has a deep, thick taproot that helps it find water in these places.

That same taproot is why it doesn’t like being moved in your garden. If you really need to, your best bet is to dig a wide hole and try to extract its taproot and as much of the soil as it’s rooted in as possible. Then, transplant it immediately. Even a successful transplant will result in a very grumpy looking plant for the first week or two.

Native range

Native across a broad swath of North America, as far west as Utah and Arizona, south to central Mexico, and north to southern Canada.

Who it feeds and shelters

Pollinators

The milkweed’s umbel structure is very accessible for sipping nectar. Lots of smaller bees, butterflies, moths, and beetles use it for this reason.

However, it’s not like the easy-access pollen buffet that carrot family plants, which also have umbels, offer pollinators. Milkweeds don’t share their pollen with insects at all. Milkweed pollen is contained in waxy sacs called pollinia. These sacs “clip” onto larger bees and wasps and hitch a ride to the next flower.

As a host and food plant

Plants in this genus are known for containing chemical compounds called cardiac glycosides, which disrupt how cells take in and push out molecules. Taking in and pushing out molecules is important for living things to go on, well, living. So most things don’t eat milkweed. Butterfly weed contains a very low concentration of these compounds, but enough that it still probably smells bad to most insects that eat plants.

A small club of specialist insects have evolved the ability to not get cardiac glycosided when they chomp on milkweed. They’ve even found a way to store those chemicals so that they can use them against the stuff that wants to eat them! This is essentially Black Panther’s superpower. The milkweed “punches” the insect (chemically), who absorbs the punch and uses it (chemically) against, for example, a hungry blue jay. In practice, blue jays mostly just avoid eating things that eat milkweed.

The best-known eater of milkweeds is of course the monarch caterpillar (Danaus plexippus). But there are others, such as the queen butterfly, the milkweed tussock moth, and milkweed beetles. Milkweed bugs, which are generalist seed eaters, can also store the cardiac glycosides from milkweeds for protection from predators.

Interestingly, a few predators, such as the black-headed grosbeak, have evolved the ability to deal with milkweed toxins because the things they eat eat milkweed. This means that milkweeds have caused an evolutionary cascade, an adaptation that’s gone from plant to herbivore to predator.

One last addendum: gray hairstreak caterpillars (Strymon melinus) sometimes eat butterfly weed flowers. This means they don’t have to deal with, and don’t get the benefit of, the cardiac glycosides.

Milkweeds have other defenses against insects, too. Butterfly weed relies on a dense covering of trichomes, or hair-like structures, on its leaves and stems. In an interview on the In Defense of Plants podcast, Dr. Rupesh Kariya describes caterpillars who eat plants with dense trichomes as basically chewing on and digesting barbed wire. It even pokes little holes in their flesh as they do. (I for one am glad my spinach leaves don’t have nails sticking out of them.)

Also worth mentioning, since it’s a common identifying feature of milkweeds, is that butterfly weed does not have thick, white, latexy sap like other milkweeds. Its sap is clear.

And one more caterpillar!

After I initially published this piece, reader commented that there’s another critter to mention here. The Unexpected Cycnia Moth (Cycnia collaris) feeds on milkweeds, especially butterfly milkweeds. The pretty white adult form of the moth is a little less charismatic than monarchs, but is just as dependent on milkweeds.

Other moths in the Cycnia genus also use milkweeds as hosts, as well as other plants in the dogbane family (Apocynaceae). These include the dogbane tiger moth and the collared cycnia.

How it spreads

Perhaps one reason Asclepias tuberosa has made a dent in common horticulture—I’ve even seen it at Home Depot—is that it’s a clumping, “polite” plant. It doesn’t spread aggressively through runners like common milkweed.

It’s a slow starter from seed, sometimes taking two or three years to bloom while it builds its deep taproot. Once established, it’ll add more stems from its crown, or the place the stems join the roots at the soil’s surface. It grows wider and taller slowly, year by year.

As I mentioned above, Asclepias tuberosa seeds spread in the wind. However—and I mean this in the nicest way—it’s not exactly an ambitious spreader. It faces quite a few barriers: not the easiest to pollinate, wind-dispersed seeds don’t land in the right spot, seeds need the cold and wet of winter to help them germinate, etc. If you want to grow more in your own garden, your best bet might be to collect the seeds yourself. Use the milk jug method to get them started and plant them the next year.

How people have used it

One of this plant’s common names is pleurisy root. (Pleurisy is inflammation in the membrane that lines the lungs and chest.) So it’s not surprising that several records in the North American Ethnobotany Database mention native peoples using this plant to treat pleurisy. Several others mention this plant in association with pulmonary trouble generally.

Pleurisy root was used as an expectorant, or something that makes your coughing more productive. This is likely why there are also records of it being used to treat other kinds of pulmonary trouble (issues affecting airways and lungs), too.

The Cherokee people, who originally populated a huge swath of what’s now the southeastern U.S., used the stems for belts.

Quick answer: you can harvest garlic after 3-5 of the lower leaves start to brown. This is usually 3 to 4 weeks after scapes appear (if you’re growing hardneck garlic). But there are a few other things you might want to know if you’re growing garlic, such as what happens if you let them flower, and how to cure and store them.

Keep an eye on your garlic plant’s leaves

Your garlic plant’s leaves are the main indicator of when you should harvest.

Garlic pushes up leaves in early spring. By the time the leaves mature, they’re usually a foot or two long, and the whole plant’s about 3 feet tall. There are somewhere between 6 and 12 of them per plant.

The leaves are edible and quite tasty, like very mild garlic. However, each one you cut means less energy gathered for the bulbs. Penn State extension recommends that if you like garlic greens, you should grow plants specifically for greens.

Leaves are also your garlic’s “paper” wrapping

The leaves extend all the way down to wrap around the bulb. The thing on the plant that looks like a stem? That’s actually your plant’s leaves folded on top of one another. And if you could see under the soil, you’d see them layered over the bulb, too.

If you planted hardneck garlic, you get scapes (or flower stalks)

As days get longer and warmer, garlic plants realize they need to make more garlic plants. Hardneck garlic puts out scapes, or a flower stalk without leaves that comes from the base of the plant. Dandelions, hostas, and day lilies also put up scapes.

Softneck garlic doesn’t (usually) put up scapes. Over thousands of years of growing it, we’ve “trained” this trait out of it.

There are two things to know about garlic scapes. First, we cut them off so that the plant doesn’t spend energy developing them. Cutting the scape makes the bulbs bigger.

Second, you should eat them. Treat them a little like a mild, vegetabley garlic clove. You can use them in stirfry, make pesto, etc.

What part of the scape do you eat

The curling stalk. Trim off the pointed end, which is stringy and a little bitter, just below the bulge. Then cut off the woody part at the other end. Sautee them, chop them and add them when you would add garlic in other recipes, etc.

If you left the scapes on, would you get seeds?

Not exactly. For reasons a little beyond the scope of this post, planting cloves for thousands of years has resulted in hardneck garlic plants that can’t make seeds.

Instead, you get something called a bulbil, which is (more or less) a tiny clove. You could plant a bulbil, but it would take roughly 3 years to turn it into a whole head of garlic. And you would need to remove it in summer and replant it every fall to prevent rot.

Leaves start to turn brown

A few weeks after the scapes, garlic plant leaves begin to turn brown and die back. This is normal. Garlic growers use it to tell them when it’s time to harvest. Here are a couple of typical rules to follow:

• Harvest when the bottom 3 to 5 leaves are brown but the top 5 are still green1

• Expect to harvest 3 or 4 weeks after scapes2

As leaves begin to turn brown, water less

At this point, the plant’s taking in a lot less water. Which means you shouldn’t give it as much as you did as it was developing. Too much moisture now might cause the bulbs to rot or break down the “paper.” It can also cause the bulb to split.3

Don’t wait for ALL the leaves to turn brown to harvest

When a leaf dies, the part of it that wraps the bulb will also wither away underground. So we don’t want all the leaves to die becase we don’t want garlic without paper skins. Then you’d have less of a bulb and more of a handful of naked cloves. This is why we harvest when some leaves are still green.

Harvest

Don’t yank! Garlic plant stems look thick, but they’re just the leaves rolled into a column. They snap easily.

Instead, loosen the soil. Most guides I’ve read suggested using a garden fork, which is sort of like a thicker, stronger version of a pitch fork. If you’ve got a lot of garlic, this makes sense. If you’re just growing a few plants in the backyard, you could just as easily use a hand fork, trowel, or soil knife (hori-hori). The point here is to loosen the soil so you can lift the whole bulb out.

If you’re growing in a pot, you could even just tip the pot over.

What does a mature bulb look like?

The mature bulb should be clearly divided into cloves. Obviously we’d also like it to be plump and bulbous, though those are relative. If the bulb still looks like a smooth, undivided whole, it’s probably not fully mature yet.

Harvest a test bulb first

It’s common advice to harvest a test bulb. That is, dig up just one to see if it looks mature or if it needs a little more time.

Supposedly you can put the test bulb back, but I’d just use it. Even if it’s small, it’ll be tasty. It’ll be mild and juicy.

You may also just be able to gently scrape away the soil from the top of the plant and see if the bulb looks mature.

Don’t harvest when it’s wet

If possible, harvest when the soil’s fairly dry, maybe after a couple days with no rain. This helps avoid soil caking on to the garlic bulb and causing rot.

If you’ve got a mulch layer—and you probably should have a mulch layer—you can pull it back a day or two before you harvest. This will help dry out the soil around the bulbs.

Curing (and storing)

Curing is the process of drying the bulb you harvested so that it’ll keep, sometimes for months. During curing, the paper dries into a protective skin, and the neck (where the leaves meet the cloves) seals shut.

You don’t need to cure before you eat. Curing is for storing. You can eat garlic immediately after harvesting.

Here’s the process for a curing:

1. Brush off loose dirt. Don’t use water! You can use your hand or a microfiber cloth. Be gentle. It’s fine if you can’t get everything off; you can try again after the bulb has dried. Don’t cut off the leaves or roots yet.

2. Hang the bulbs or lay them on a rack. Put them somewhere dry, out of the sun, and with good airflow. A fan can help, even if it’s not pointed directly at the garlic.

3. After a few weeks, the necks should be dry. The skins should be papery. The roots should feel wiry.

4. Now’s a good time to try cleaning the garlic again, since the soil should be dry and less clingy. Trim the roots and cut the leaves back to about an inch above the clove. (If you’re growing softneck garlic, you can supossedly use the leaves to braid them. As a New Englander, I don’t know anything about braiding garlic and refuse to learn.)

5. Store them somewhere cool with good airflow. In a kitchen that’s not too warm and humid, they may last a month or two. Some people also pickle garlic cloves for even longer storage. I know people who keep them in mesh bags, cardboard boxes, and paper bags. (Avoid plastic bags or tupperware.)

“Optimal” storage

The University of Massachusetts has a more detailed guide to curing and storing. It’s written for people who have a whole field of garlic, but it’s useful for us backyard operators, too.

The guide says that you can keep bulbs for 6 to 7 months if you store them somewhere with low humidity, good airflow, and at just above freezing (32°F / 0°C). I’m not sure how you’d achieve that without a dedicated fridge set to a low temperature, but if you have the option, you can keep garlic for much longer.

Storage “gotchas”

Fridges

You might think, “If 32 degrees gets you 7 months, and my kitchen counter gets me 2 months, I should store it in my fridge, and get like 3 or 4 months.” That’s both reasonable and might backfire.

Garlic uses temperature as a signal for growth. It needs a cold period to “know” that winter’s passed, and then it sprouts best between 40-50°F (4-10°C).

So if you keep it at 32°F / 0°C, it thinks it’s winter and stays dormant. If you keep it at 60°F / 15°C, it’s less likely to sprout, since the sprouting band is 40-50°F.

Unfortunately, fridge temperatures are in a sort of reverse sweet spot where garlic gets its “winter” signal and its “sprouting” signal. So that’s often the worst place you can store bulbs, unless you can guarantee that your fridge is a constant 34ish°F. (Like maybe nobody ever opens the door.)

In addition, fridges can be humid, which can create rot.

Freezers

On the other end of spectrum, freezing temperatures can freeze the water inside the clove, which can cause damage. If you want to freeze garlic, peel and chop the cloves.

Plants in Plain Language is free. Subscribe to get fun and plant nerdery in your inbox.

You can also help me rationalize spending even more time on this—writing, researching, trying to get photos of very spontaneous bees—by buying me a coffee or becoming a monthly sponsor.

Their most recent research was on goldenrods, the Solidago genus. This is a group with a bit of a jagged reputation. They’re falsely blamed for causing allergies. (Their pollen spreads on bees, not the wind.) They’re keystone species because of their immense value to wildlife. They’re perceived as weedy and aggressive. A couple of species are quite ambitious. Canada goldenrod and smooth goldenrod, for example, are genuine problems in Europe. But there are more than 100 species in this genus, most of which are perfectly “polite” in the garden.

Various gardening podcasts and articles have covered the “top performing”1 goldenrods in the trial. That is, the ones that looked good, bloomed prolifically, resisted disease, etc. But I’m going to focus on the trial’s data on insect interaction. I want to know which goldenrods might conjure the coolest and most interesting bugs to run after and make the subject of clumsy, blurry photographs.

Alternatively, if you’re not into bugs, then which goldenrods will conjure the most food for cool and interesting birds. Hummingbirds, for example, need protein, and they can’t get it from the red plastic feeder. They eat ants, mosquitoes, weevils. They even raid spiderwebs—both for the spider’s meal and the spider. So in a way, a goldenrod is a hummingbird feeder.

The top goldenrods by wildlife

The trial data comes from regular observations of 70 goldenrods between May and November over 3 years. A researcher would go stare at a cluster of flowers for 60 seconds and write down what they saw. From this, they extracted a couple of metrics:

• Average insects per observation: The total number of insects they saw divided by the total number of observations.

• Total bumble bee observations: Raw count of bumble bees over the course of the observations.2

One caveat. Mt. Cuba describes the trial as happening in “full sun in ‘average’ garden soil best described as a clay-loam with a pH near 6.5.” And it’s in Delaware, in zone 7a. So the conditions here might not be perfect for a forest-dwelling goldenrod more at home in northern Maine.

Still, the results are interesting, and competition is fun. So in this post, I’m going to report on the top goldenrods across these two metrics, average insects and bees.

Note: I’m leaving one species, Sand or Locust Fork goldenrod (Solidago arenicola) out, even though it wiped the floor with the competition as far as bumble bee visits go. It has a small, very specific native range, and doesn’t seem like something you’d be able to easily purchase seeds for, anyway.

Leavenworth’s goldenrod (Solidago leavenworthii)

• Insects per observation: 12.37 (1st place)

• Bumble bee observations: 74 (4th place, tied)

I must emphasize how much this plant won the “insects per observations” category. The average insects across trial plants was 3.3 per observation. That’s actually pretty good. Go look at a flower in your garden for a minute, and you might not see 3 insects. But Leavenworth’s goldenrod averaged 12.37 per observation!

A few things might’ve contributed to this. First, it’s a very large plant, the largest in the trial, with a huge number of flowers, perhaps as many as 350. It also bloomed late in the year in Delaware, October and November. Perhaps it was the main thing available, even as many insects were beginning to pack it in for the winter.

Mt. Cuba assigned it a score of 3.5 because its foliage tended to flop. One tool we sometimes use to prevent floppiness is the so-called Chelsea chop, where you cut a plant back by about a third to keep it shorter and neater. Unfortunately, Leavenworth’s probably isn’t a candidate for this, since it already blooms late. Chelsea chopping delays flowering. In this case, it might delay it until after most pollinators can use it.

Leavenworth’s goldenrod is native to the southeastern U.S. north to the mid-Atlantic. It lives in bogs and along coastal plains. (A coastal plain is flat, low elevation land near the coast.)

See Mt. Cuba’s summary for Leavenworth’s goldenrod.

Facts for gardeners

• Height: About 8 feet

• Moisture: Native to wet and boggy soils, but Mt. Cuba’s data says it’s also fine in dryer soils.

• Sun: Full sun, not shade tolerant.

• Bloomed in Delaware: Late fall, October through November in Delaware.

• How it spreads: Ambitiously, even aggressively, through rhizomes. Will create large drifts. (Seeds also spread in wind.)

Editorial note: Might look good alongside Joe Pye or ironweed, especially in a larger space.

Riddell’s flat-top goldenrod (Solidago riddellii or Oligoneuron riddellii)

Note: I included the second latin name because I saw at least one well-known seed seller using it. The reason there are two latin names is that taxonomists are having an argument that’s at once perfectly reasonable and annoying to those of us who like to think latin names are stable.

• Insects per observation: 9.15 (2nd place)

• Bumble bee observations: 86 (3rd place)

This plant was an insect favorite. Its overall score was only 3.7, a little lower than the top plants because it had a tendency to flop. 3

However, to be fair to other species that “performed worse,” this plant really benefits from the way Mt. Cuba collects data. Riddell’s only blooms for a couple weeks. This means all of its flowers open basically at the same time—and it may have around 450 flowers per plant.

Mt. Cuba measures insect visits per 60 seconds. If all of your flowers are open at once, you’re likely to get more in 60 seconds than if you bloom over a long period of time, and only some of your flowers are open. (This makes Leavenworth’s goldenrod, which blooms over a couple months, even more impressive to me!).

That said, it also benefits from its flower structure. Like a few other goldenrods, Riddell’s has flat-topped corymbs, essentially a flat landing pad made of flowers.4 This makes flower access potentially easier than the wands and spikes other goldenrods feature.

This is a midwestern species that lives in wet meadows and near waterways. Think “sunny rain garden,” right next to your irises.

Mt. Cuba’s summary of Riddell’s goldenrod.

Facts for gardeners

• Height: About 5 feet

• Moisture: Wants moist soil, though it did well in the “average” conditions of Mt. Cuba’s trial garden.

• Sun: Full sun, not shade tolerant

• Bloomed in Delaware: September

• How it spreads: Seeds spread in wind. Also has short rhizomes that let it form “well-behaved” clumps.

Atlantic goldenrod (Solidago arguta)

Other common names for this species include forest goldenrod and cut-leaf goldenrod.

• Insects per observation: 7.25 (3rd)

• Bumble bee observations: 74 (4th place, tied)

This goldenrod would’ve preferred the dappled light of a forest edge to the full sun of the trial garden. It nevertheless did extremely well—at least as far as feeding the insects goes. A last factor might be because it bloomed basically all fall, late August to late October.

Solidago arguta has a flower structure that could also be a great band name: pyramidal plumes. In botany, this name refers to a structure where a central stem supports a tower of flowering stems that’s widest at the bottom. Some plume-creating flowers, like Solidago arguta, only create flowers along the upper part of the stems, instead of all around. This is called a pyramidal secund (with a “u”) plume.

This plant is normally found near forests across the eastern U.S. and into Canada. Its overall score was 3.5. Mt. Cuba reported that its “stems tended to flop and the foliage was affected by lace bug and powdery mildew,” but also that it might’ve done better “if provided some shade and drier soils.”

Mt. Cuba Center’s summary of Atlantic goldenrod.

Facts for gardeners

• Height: Mt. Cuba says 5.5 to 7.5 feet. Possibly much shorter (2-3 feet) in the shadier habitats it typically grows in, though.

• Sun: Very shade tolerant. May have suffered appearance wise a little in full sun (though Mt. Cuba suggests the issue may actually have been moisture.)

• Bloomed in Delaware: Late August to late October.

• Moisture: Prefers dryer soils.

• How it spreads: Seeds spread in wind. Also has short rhizomes that let it form “well-behaved” clumps.

Mountain goldenrod (Solidago curtisii)

Note: In researching for this piece, I stumbled on another species, Solidago flaccidifolia, that’s so similar to this one that they might just be varieties of each other. And its common names are mountain goldenrod or mountain decumbent goldenrod.

• Insects per observation: 6.58 (4th place)

• Bumble bee observations: 118 (2nd place)

This was the 4th highest insect count in the trial. It was 2nd for bumble bees—and by a lot.

This goldenrod’s associated with the southern portion of the Appalachian Mountains. It’s native through the mountainous southeastern U.S. as far north as the mid-Atlantic states (e.g. Pennsylvania, Delaware). It’s a woodland plant, at home in the shady understory, though it apparently also did very well in the full sun conditions of the trial. Mt. Cuba assigned it a trial score of 3.9, in the top 20% of species.

Mt. Cuba Center’s summary of mountain goldenrod.

Facts for gardeners

• Height: Mt. Cuba says about 6 feet. However, this is another case where it might grow much shorter, e.g. 1-3 feet, with shade.

• Sun: Can handle both full sun and a lot of shade.

• Bloomed in Delaware: September to October.

• Moisture: Not too wet. Think, “Lives in the dry, shady understory of a mountain forest.”

• How it spreads: Seeds spread in wind. Also has short rhizomes that let it form “well-behaved” clumps.

Showy goldenrod (Solidago speciosa)

• Insects per observation: 6.05 (8th place, tied)

• Bumble bee observations: 51 (8th place)

This species didn’t do as well as the others I’m writing about, and Mt. Cuba only assigned it a 3.4 overall (for floppy stems and a poor floral display). However, it’s more promising than it looks. The average insects score of plants 4th-9th was, on average, 6.32—only slightly higher than this one. And Mt. Cuba’s own analysis is that it would do better in rockier, dryer soils. In its home habitat, it’s a pretty stunning plant.

Showy goldenrod is native basically across the entire eastern half of the U.S. It’s found in sandy prairies and dry open fields.

Mt. Cuba Center’s summary of showy goldenrod.

Facts for gardeners

• Height: About 5 feet

• Sun: Full. Not shade tolerant

• Bloomed in Delaware: mid September through late October. Pretty impressive!

• Moisture: Prefers dry soil.

• How it spreads: Seeds spread in wind.Also has short rhizomes that create clumps.

Plants in Plain Language is free. Subscribe to get fun and plant nerdery in your inbox.

You can also help me rationalize spending even more time on this—writing, researching, trying to get photos of very spontaneous bees—by buying me a coffee or becoming a monthly sponsor.

Iris people have decided, for whatever reason, that there’s not enough jargon in botany, and they need to come up with their own. Admittedly, theirs is cooler. For example, instead of sepals and petals, they talk about falls and standards. Throughout this piece, I’ll write the “normal” botanical word first and the Iris Talk word second, e.g. "sepals (falls).”

What it looks like

Northern blue flag is about two or three feet tall from its base to the top of its flowers. A mature clump may send up four or five blooms, usually not at the same time.1 It’s a solidly medium-sized iris, though smaller than the hulks commonly sold at nurseries, such as Siberian irises and bearded irises. Still, it holds its own in the area most people come to irises for, the flowers.

Iris flowers are the muscle cars of the gardening world: they’re loud, colorful, and run out of gas kind of quickly. My blue flags, for example, flower in late May and finish up in June. They’re mostly purple with deep purple veins and three yellow signal blazes, or signals.

Northern blue flag flowers are not subtle. Here are the major pieces, which sit on top of each other like an interlocking layer cake.

• Three large, drooping sepals (falls) that end in yellow signals. The signal isn’t just for you. It’s also a landing strip for bees.

• Three rounded, lightly veined petals (standards) sit in the gaps between sepals.

• Three rectangular style arms hover over the sepals. These are actually modified pistils, the female reproductive part of a flower.

The purple veining persists through the signal, which is one of the cool and distinguishing features of this species. Supposedly this helps you distinguish it from southern blue flag. However, there are lots of research grade observations on iNaturalist where the southern species also has heavy purple veining.

Iris leaves, including Iris versicolor’s, are one of the defining features of the family they belong to, Iridaceae. They’re long, narrow, pointed, and often described as “swordlike.” Unnecessarily, there are 2 technical terms for this structure: ensiform or gladiate. Ensiform is from the Latin ensisformis, or sword shape. Gladiate comes from gladius, or sword. They also spread out in a fan from the base.

A bizarre feature of iris leaves is that they’re folded in half, like someone’s begun a paper airplane. This is easiest to see at the base, where the fold is open enough to clasp the stem. As you move up the leaves, though, they fuse together. This means you are always looking at the lower side of the leaf (the abaxial side). The upper leaf (adaxial side) is enclosed in the fold.

Where it lives

Habitat

This is a plant that lives for summer vacation: wet feet and sun and acidic, rich soil. Okay, the last one’s not a fit, but it’s useful if you want to learn what it likes.

Northern blue flag grows along streambanks, shorelines, marshes and sedge meadows. A sedge meadow is a type of wetland populated by sedges and water-loving grasses.

Let’s dwell for a moment here, since it tells us about the niche this plant fills—not just the ecological one, but the horticultural one. Maybe you don’t live on a river. But do you have a wet, mucky place in your yard? This plant would like to go there. Clay soil? Put it there. Part of the yard that gets flooded? Put several of it there and let it start a rain garden. One university extension article suggests it does fine even under “4 inches of standing water.” Just make sure it gets a lot of sun.

Native range

Northern blue flag iris is native to the eastern U.S. and parts of southern Canada. Its range stretches south to the northern edge of Florida. It also grows in the north central part of North America, including Iowa, Minnesota, Michigan, and the southern edges of Manitoba and Ontario.

By comparison, southern blue flag’s range extends from Florida north to the mid-Atlantic. It extends further west, too; the northern species peters out before reaching much of the south central U.S.

Who it feeds and shelters

Pollinators

Mostly pollinated by bumble bees and long-horned bees. Hummingbirds, hummingbird moths, and butterflies are also sometimes attracted to the flowers.

The sepals (or falls, or just “the big showy parts”) work like landing pads that guide visitors to nectar. To do this, they have to brush past the anthers, getting coated with pollen in the process.

Host plant

In its native habitat, northern blue flag provides shelter for amphibians and insects. It hosts a handful of butterflies and moths, such as the Iris borer moth (Macronoctua onusta), Virginia ctenucha (Ctenucha virginica), and according to at least 1 iNaturalist observation, the smeared dagger (Acronicta oblinita).2

Weevils, flies, aphids, and other insects feed on this plant, but as usual, there’s a little less interest in things that aren’t Lepidoptera (butterflies and moths).

Poisonous for mammals

Iris versicolor’s roots and leaves contain a chemical called irisin or iridin, which is what several sources delicately refer to as a “purgative irritant.” Means that eating irises can cause uncontrollable pooping. Not great—unless you are a gardener hoping to plant something deer and rabbit won’t eat.3

How it spreads

Spreads through roots (rhizomatously) and seeds. A rhizome is technically an underground stem that can sprout new shoots and roots—and whole new plants. When it spreads this way it forms clumps, and eventually whole colonies. Its seeds often float away to a new location in water. Spreading seeds this way is called hydrochory.

You can divide northern blue flag

To divide a clump of northern blue flag, dig it up and pull the rhizomes apart, making sure each has at least a fan of foliage and some roots. Then replant them.

How people have used it

Various Native American peoples used this plant’s roots for a variety of reasons, including treating wounds and dressing burns.4 Two peoples, Mi’kmaq (or Micmac) and Penobscot, both indigenous to what is now the U.S. northeast and southern Canada, may have used it for treating cholera.

As a reminder: this plant’s roots are poisonous for mammals. Presumably people who used it knew how to prepare it. You shouldn’t if you don’t!

The Potawatomi people (Great Lakes region) used the leaves in basket weaving.

Iris versicolor is the official provincial flower of Québec.

Subscribe now

Northern vs. southern blue flag (Iris virginica)

The most reliable difference between northern blue flag and southern blue flag is that the northern’s flowers are taller than its leaves. On southern blue flag, the leaves extend above the flowers.

Supposedly their colors differ. For example, northern blue flag’s flowers are often described as deeper violet with more prominent veining, and southern blue flag’s signal is a brighter yellow. However, I’ve now spent quite a lot of time looking at both species. And these things tend to be true on average. Which I don’t find all that useful for confidently identifying a plant.

The northern species is cold hardier, the southern heat hardier. But also, they hybridize where their ranges overlap, making the whole idea of distinguishing them a bit of a fool’s errand.

And they start from a seed that’s about the same size as the sprinkles you top your ice cream with.

Seeds germinate all the time, in places you put them and places you didn’t. It’s therefore easy to overlook these little botanical starter kits. And honestly, while giant sequoias are magical, so’s the much more diminutive Pennsylvania Sedge, which blooms like a firework that’s afraid to make noise. A seed made that—or at least made it possible.

Let’s take back the “seed funding” metaphor from the business folks for a minute. You, the gardener, are an investor. You want your seed to become a seedling. And then eventually to have enough resources to start manufacturing cucumbers or flowers or whatever. But you’re not in there doing the day-to-day tasks of absorbing sunlight, converting it to chemical energy, taking up nutrients, and so on. You’ll just be having regular chats with senior leadership, making sure they have what they need.

And the first thing they need, long before they set down literal roots, is less (chemical) red tape.

The right conditions

Summer vegetable and herb seeds require very little work to get started because we’ve spent so much time breeding them that way. Biologists even have a name for this: easy, quick germination is part of a suite of characteristics associated with “domestication syndrome.” That is, people have selected for them so that they could more easily grow food.

The peppers, cucumbers, zinnias, cosmos, and melons you want to grow in the summer will germinate if you follow the instructions on their seed packs. To take this a step further, you could learn a little about where they’re from, and what conditions they’ve adapted to.

Peppers, for example, are probably from tropical parts of Peru, Ecuador, and Colombia. This is why pepper seed packs tell you they germinate best when the soil’s warmer (around 80°F, 26°C). Most people don’t have any 80°F soil lying around when it’s pepper-starting time. You can fake it though with a heating mat or a little greenhouse cover on your seed starting tray.

Seeds that haven’t been “domesticated” have dormancy mechanisms

If people haven’t spent thousands (and thousands) of years domesticating a plant, then its seeds probably still have dormancy mechanisms. These keep them “asleep” until the right moment, or as a biologist might put it, in “synchronization with the environment.”1

For example, species that are native to cold places, such as black-eyed Susans2, anise hyssop, and coreopsis, have a hard seed coat that prevents water from getting in and starting the seed’s engines at the wrong time. Imagine you are a seed from a cold place. You don’t want to germinate on a warm October day and then get hit by winter’s long, cold truck. To keep from doing this, you have a hard seed coat that “melts away” over months of cold and wet, i.e. winter.

In addition to the physical barrier, winter-dormant seeds have a chemical layer of protection. Winter reduces hormones that prevent growth (such as abscisic acid) and increasing ones that encourage it (such as gibberellic acid). This allows plants to germinate when it warms up in the spring.

Winter isn’t the only condition that’s dangerous for plants. Death Valley, California, gets about 2 inches of rain per year. (We got that here in New England last week.) So species like summer poppy (Kallstroemia grandiflora) and devil’s claw (Proboscidea parviflora) have a sort of “checklist” for when it’s ok to grow. They need an inch or so in autumn, and then another inch through March.

Other species, like wild lilacs (Ceoanthus species) use fire as an indicator. This clever mechanism allows them to grow when there’s not as much competition, and when they’re less likely to be shaded out. They can sit in the soil for more than 200 years waiting for the right time.

The native-seed-starting gardener needs to learn some new vocabulary

Breaking dormancy is probably one of the barriers for people interested in starting native plants from seed. In theory, you could hurl them into your garden and ask your preferred deity to take the wheel. But most gardeners want to feel more confident about planting.

Fortunately, native plant people have some tricks. For example, you can use the milk jug method for seeds that need cold and wet (stratification), a method invented by American gardener Trudi Davidoff in collaboration with the U.S. Department of Agriculture. Davidoff supposedly said, “If it’s not easy, you’re doing it wrong.”

Imbibition

Once dormancy “breaks” and conditions are right (warm enough, moist enough, etc.), the seed’s ready to grow. Next is imbibition. Imbibe means to drink, and that’s what the seed does—takes in water. Internal enzymes activate. Energy stored in chemical form releases.

The seed is not getting light or nutrients at this point. Just water and oxygen. Oddly, it may be “aware” that there’s light close by, since that’s a germination cue, but it doesn’t have any way to photosynthesize yet.

Finally, the seed root, or radicle, emerges.3 It takes in water and nutrients from the soil or whatever medium you’re growing it in. This is a delicate time. If the radicle rots, the seedling will die. This is called damping off and is a big reason that when you start seeds indoors, you should use a mix designed to have plenty of drainage.

The seed stem (hypocotyl) pushes up next. This is often the first thing the attentive gardener notices. Once the seed stem breaks the soil surface, it turns green. In many species, it’s bent over like a hook shape to protect the delicate tip. As it comes up, friction with the soil usually helps pull the seed cap away, though sometimes you’ll see it get stuck on top of the stem. You can gently brush it away if it doesn’t fall off on its own.

As an aside: This is a reason it’s important not to plant your seeds too deep. It takes precious energy to push up to the surface. A paper published by the USDA’s research division dryly reports that deeply-planted seeds might germinate, but “seed reserves may be exhausted before the seedling reaches the soil surface, which leads to seedling death.”

Finally, plants unfurl their cotyledons, or seed leaves.

Cotyledons are packed with nutrients from when the seed was formed. Seedlings can break these nutrients down and use them. Some species have two (dicots), and others have just one (monocots). Some keep them underground, where they provide nutrients, and others above ground, where they start photosynthesizing.

Most seeds’ supplies will be running a little low after accomplishing all this. They’ll have to begin gathering what they need from their environment.

How does the seedling know which direction is “down”?

Plants have a very cool way of knowing which direction to grow. Plant cells have little components called statoliths. These are heavy and settle on the bottom of the cell. Plants are able to use the location of these statoliths to “figure out” which way is down. Essentially, they can sense gravity.

This is why no matter which direction you plant a seed in, the radicle will grow down, even if it has to curve.

Plants can also sense light and move toward it. But this phototropism is separate from the gravitropism that helps the root grow in the right direction.

Indiana University has a very cool video of corn seed radicles emerging and growing in the right direction, even though seeds are oriented in different directions.

Plants in Plain Language is free. You can subscribe for weekly fun and plant nerdery in your inbox.

You can also help me rationalize spending even more time on this—writing, researching, trying to get photos of very spontaneous bees—by buying me a coffee or becoming a monthly sponsor.

Ranunculaceae is a family of at least 3,700 species. Here are some you might know:

• Ranunculus (Ranunculus spp.)

• Columbine (Aquilegia spp.)

• Hellebores (Helleborus spp.)

• Anemones (Anemone spp.)

• Clematis (Clematis spp.)

• Marsh marigold (Caltha palustris)

• Larkspurs and delphiniums (Delphinium spp.)

• Hepatica (Hepatica spp.)

• Lesser celandine (Ficaria verna), though not greater celandine, which is in the poppy family

Common characteristics

Flowers have many stamens and (usually) many carpels

The most reliable characteristic of this family is one you need to look closely to see: lots of stamens and carpels.

Ranunculaceae species often have dozens and dozens of stamens. Many species also have lots of carpels, though not always.

Flowers: with lots of exceptions, appear to have five petals and are symmetrical in more than one way

Ask this family how many petals it has, and like a teenager describing what it did in school that day, it’ll say, “Oh, five.” In fact, it often has more than five, and some of its petals are actually sepals. But it doesn’t want to get into the details with you.

Flowers in the Ranunculus genus do usually have five petals. And a few other genera, like Anemone, appear to have five petals, but actually have sepals that look like petals. Sepals are leaf-like structures that protect flowers. Botanists distinguish them based on the type of tissue they’re from, which doesn’t help us much as identifiers without microscopes.

Another sometimes-works identifier is that many flowers in this family are radially symmetric, or symmetrical in more than one way. There’s even another trivia word for this, actinomorphic.

Unfortunately, there are exceptions. For example, plants in the monkshood and delphinium genera can only be divided in half one way. The terms for this are bilaterally symmetrical or zygomorphic.

Lobed, alternate leaves

Most plants in this family have leaves with deep grooves in them. They also usually alternate on their way along a stem (they don’t grow across from each other).

Of course there are exceptions. Lesser celandine (Ficaria verna), a destructive invasive here in the U.S., has leaves with gently waving edges and a notch at the base.

Foragers beware: Most buttercup family plants are toxic

Ranunculaceae contain chemicals that can cause blisters and rashes. A very cool bit of plant engineering makes this possible.

They can’t store the blister- and rash-causing substance, called protoanemonin, directly. That would harm their own tissues. Instead, they store it in a chemical form called ranunculin, a little plant biohazard container. When something chews on the plant, it releases enzymes that open the container, which “sprays”—to use some artistic license—the protoanemonin all over the unsuspecting herbivore.

For this reason, it is better to be a suspecting herbivore. Don’t eat plants in this family, and tell your pets not to, either.

Wildlife value

As pollinator plants

Many Ranunculaceae bloom in spring, which is important for early-emerging pollinators. Where I live in the U.S. northeast, these include bumble bee queens, mining bees (Andrena species), a few species of cellophane bees (Colletes spp.), and some hoverflies.

For example, red columbine (Aquilegia canadensis) is an early-bloomer known for attracting hummingbirds. A couple of species of globeflowers in Europe and China have been studied because of their specialized fly pollinators. And in the U.K., stinking hellebore (Helleborus foetidus) is an important food source for bumble bees in February. (Incidentally, I recently wrote about a phenomenon where yeasts heat up the nectar in early-blooming hellebores, creating little saunas for bumble bees.)

Many species in this family are not just early bloomers but spring ephemerals, plants that flower and set fruit before trees put out their leaves. They bloom especially early, when very few other plants have emerged. Though they provide critical food for early-emerging insects, they also have to jump through a few hoops to make sure they attract those insects.

For example, one interesting study proposes that star-shaped winter aconite (Eranthis stellata) has evolved “elaborate petals” with “multiple functions, including color contrast, [guides for finding the nectar], a nectar reward for bees, and food deception and a pollen reward for flies.” This is a lot more work than your typical fall-blooming aster has to do, for example.

One paper found that five early-season Ranunculaceae species produced pollen but almost no nectar. This is interesting in that it speaks to early-season bees especially needing the protein- and fat-containing pollen for rearing their offspring.

For shelter and food

Most mammals don’t want to eat Ranunculaceae plants, given the whole blistering-the-inside-of-your-mouth thing. That said, they may be willing to take a chomp if they’re desperate or if the plants are young and unestablished. And evolution’s creative. A few insects actually do tolerate the chemical weaponry.

A leaf mining fly, Phytomyza ranunculi, lays its eggs on plants in this family. Leaf mining is a way of feeding where insects eat the inner tissue of leaves.

Two generalist caterpillars include Ranunculaceae plants in their diet, too: the Hebrew character (Orthosia gothica) and the small angle shades (Euplexia lucipara).

Interestingly—if you are a nerd—a few other moths are thought to eat Ranunculaceae, but perhaps incorrectly. For example, a few sources list monkshood (Aconitum spp.) as a food source. But in a 2021 paper, a researcher observed “high mortality rates among larvae” that were fed monkshood compared to ones fed dandelions.

Value for people

We eat almost nothing from this family with one notable exception. We use the seeds of Nigella sativa as a spice (black cumin or black seed), particularly in Indian, Middle Eastern, and North African cooking.

We do like looking at them, though. Popular garden plants include hellebores, larkspur, delphinium, and various species of clematis. Marsh marigold (Caltha palustris) is beloved among native plant nerds where I live, though perhaps not as much as red columbine.

Several plants are medicinally important within their cultural contexts, too. These include the previously mentioned black cumin, black cohosh (Actaea racemosa), and goldthread (Coptis spp.).

The ranunculus from the flower shop

You might include ranunculi in arrangements you bring home from the florist. The Ranunculus genus, by the way, includes some 1,600 species and has been bothering taxonomists for centuries. (A 2010 paper recommended splitting it into multiple genera.)

But the ones we get from the florist are, in some ways, less interesting than those we don’t. Like roses, these have been bred to look more attractive to people and to be less useful to wildlife. For example, cultivated ranunculi tend to have double flowers, which means a lot more petals and less pollen, nectar, and accessibility for pollinators.

Main sources

Family characteristics

• A molecular phylogeny, morphology and classification of genera of

  Ranunculeae (Ranunculaceae) | Taxon, accessed through Wayback Machine

• Ranunculaceae | Wikipedia

• Ranunculaceae Juss. | World Flora Online

• Ranunculaceae in Flora of North America | efloras.org

• Plant Taxonomy 10a3, Ranunculaceae | Nic Tippery, YouTube

• RANUNCULACEAE | Botanical Dermatology Database (Has a huge species list, though not a particularly accessible website)

Ecology

• Feeding the bees in winter | Bumble bee Conservation Trust

• Life history of the rare boreal tiger moth Arctia menetriesii (Eversmann, 1846) (Lepidoptera, Erebidae, Arctiinae) in the Russian Far East

• Phytomyza ranunculi | NatureSpot

• Picking Plants for Pollinators: The Cultivar Conundrum | Xerces Society

• Pollen food resources to help pollinators. A study of five Ranunculaceae species in urban forest | Urban Forestry & Urban Greening, 2021

• Pollination Strategies of Eranthis stellata (Ranunculaceae), a Spring Ephemeral with Elaborate Petals | Biology, accessed through PMC

• Nectar yeasts warm the flowers of a winter-blooming plant | Proc Biol Sci, accessed through PMC

This post is a summary of a study, “Nectar yeasts warm the flowers of a winter-blooming plant,” published by Carlos Herrera and María Pozo in 2010 in Proceedings of the Royal Society B: Biological Sciences, available open access through PubMed. Because it makes for a more complete and interesting story, it also covers some of the authors’ follow-up research.

What they studied and why

There are yeasts out there in the world. A yeast is a lifestyle choice, where a fungus lives as a single-celled organism that reproduces through budding or fission. Later, maybe it’ll transition to being a strand of cells that graffitis old bread with colorful fuzz.

Anyway, it’s probably freeing to live as a yeast, because you can do it all over the world, from deep-sea vents to arctic soils to the nectar in flowers.

Nectar’s a nice place to be if you’re living as a yeast. It’s got lots of sugar that you can metabolize, a process where you absorb energy from sugar molecules. When you do this, you create a little burst of heat.

In a 2010 study, researchers Carlos Herrera and María Pozo wanted to learn if yeast metabolism makes enough heat to actually warm up nectar, as well as the air around the nectar. The specific fungus in this study is Metschnikowia reukaufii, which spends most of its life as a yeast and specializes in flower nectar.

Why is this interesting? A 2008 study that Herrera co-authored found that yeasts actually hitch rides to flowers on bumble bees.

The two bumble bees in that study, early bumble bee (Bombus pratorum) and buff-tailed bumble bee (Bombus terrestris), were on their way to and from a plant called stinking hellebore (Helleborus foetidus). These bumble bees are known as important early pollinators of stinking hellebore—or you could flip the relationship and say that stinking hellebore is known as a critical early-season food source for bumble bees.

So, bumble bees bring yeasts to flowers, and yeasts eat the sugar in nectar and release heat. If that heat is enough to warm the nectar, then perhaps it’s a little like offering the bumble bee a warm bath on a cold day. Bees might be more likely to visit a flower if they get a free spa session along with their meal, which would improve the flower’s reproductive odds. This is rose-colored glasses ecology: a little love triangle involving three separate kingdoms where everybody’s getting what they need.

On the other hand, making heat requires the yeast to eat the sugar. Eat enough sugar and there won’t be much left in the nectar. Bees would then visit less, flowers would have less sex. This is a more ominous picture; the yeast is acting as a parasite on the relationship between flowers and bees.

Two sites, two locations, two experiments

Researchers located two clusters of stinking hellebores at two different locations. They tested flowers in pairs, 7 pairs at site one, 10 pairs at site two. One of each pair was left alone (the control), and the other was modified (experiment or treatment).

Experiment One prevented flowers from developing yeast. Experiment Two added extra yeast. They also bagged experiment flowers so pollinators couldn’t get to them. This prevented bees from bringing yeast to treatment flowers in Experiment One, and from modifying yeast amounts for treatment flowers in Experiment Two.

Then, on whatever day was designated Official Experiment Day, they measured the temperatures of the nectar and the air just above the nectar.

They ran Experiment One at both sites and Experiment Two only at one. They don’t say why; I assume it was for a typical something-logistical-went-wrong reason.

Both locations, by the way, were in the mountains in Spain, in the understory of a black pine forest. Bumble bees visited regularly throughout the experiment, though they couldn’t access the bagged flowers.

About stinking hellebore

Helleborus foetidus is a buttercup family species (Ranunculaceae) that blooms in very early spring, February to April, depending on the location. It’s native across western Europe and in the U.K.

Stinking hellebore creates clusters of flowers, sometimes as many as 75 per cluster. Each flower contains 5 nectaries, and each of those contains up to 5 microliters of nectar. A microliter is a millionth of a liter. If it helps you visualize: there are about 4,930 microliters in a teaspoon. And an aside, it boggles the mind that we can know how much nectar is in a flower’s nectary.

This nectar being available early in the year is what’s key. For example, a Royal Horticultural Society article observes that stinking hellebore is a “wonderful native plant that flowers in even the coldest weather and is adored by bees.”

That yeasts might warm these flowers in cold weather, further benefiting bees, is a lovely idea—the kind of neat summary that makes us think nature’s got everything figured out. But let’s not get ahead of ourselves. Is yeast actually warming flowers? And if it does, is that actually good?

What they found

All the unbagged (control) flowers had yeasts, which is what one would expect with regular bumble bee visitors. Interestingly, the interiors of all flowers, even unyeasted ones, were warmer than the air around them. Herrera and Pozo suggest that this is because of the stamens and carpels, or reproductive parts, breathing. (All parts of plants “breathe,” or release carbon dioxide and some heat, but I’d speculate that the stamens and carpels do so more than other plant parts, which is why they’re being highlighted here.)

But the yeasty flowers were warmest. Here’s a summary of how much warmer the nectar and flower air were compared to the ambient air.

• Experiment 1, Treatment (yeasts removed): Nectar 1.6°C warmer, flower air 0.8°C warmer

• Experiment 1, Control (left alone): Nectar 3.1°C, flower air 1.2°C

• Experiment 2, Treatment (yeasts added): Nectar 1.9°C, flower air 0.7°C

• Experiment 2, Control (left alone): Nectar 1°C, flower air 0.5°C

A few notes on these results:

1. To convert temperatures to Fahrenheit, multiply by 1.8. So 3.1°C is about 5.6°F.

2. Flower air specifically refers to the air inside the flower, immediately near to the nectar. The authors refer to it as the microenvironment inside the flower.

3. You might be wondering, why did the control in experiment 1 get so warm? The paper doesn’t explicitly address this, but a couple things are relevant. First, they only did experiment 2 at one of their 2 study sites, so there’s different data underneath those numbers. Second, they did experiment 1 in March and experiment 2 in April. The weather was different, the bee visits were different, etc.

4. You want this to be a table. I also want this to be a table. As far as I know, there’s no way to create an accessible table on Substack. So we’re stuck with bullets.

The authors do some weedsy number crunching with their results that you should review if you’re interested. For our purposes, their key takeaways are that more yeast results in higher temperatures. Every tenfold increase in yeast means about .66°C (1.2°F) warmer nectar. Individual flowers with very high yeast densities had nectar that was 5-6°C (9-11°F) warmer than the outside air. That’s much, much warmer. Imagine if someone you lived with turned your thermostat up that much. You would notice.

The high temperatures weren’t outliers, either. The researchers report that about 20% of nectaries in exposed flowers were at least 4°C warmer than the surrounding air.

What it means (the “so what?”)

As a reminder, the scope of this paper is narrow. The researchers just wanted to know if yeasts make nectar and flower air temperature warmer. That’s it. Their results don’t tell us about bumble bees treating nectar as a warm cup of tea on a cold day, or yeasts parasitizing the bee/hellebore relationship. A difficult thing about science is that it takes tiny steps, each of which generally needs some argument. Such is the nature of making knowledge.

That said, the researchers are absolutely interested in all of those things. So the “so what?” includes both “what this tells us” and “what this implies could be true (and should be studied).”

Ecological throuples

This study is about three species from three different kingdoms in a relationship with each other. Bumble bees go to flowers for nectar. Yeasts hitch a ride on bumblebees, also for nectar. Once yeasts are in nectar, the heat they put off might attract more bumblebees.

Even if there was nothing else to learn, that’s an eye-opener. Next time you see a bumble bee on a flower, know that you might be—probably are—seeing a three-way interaction.

A third way that flowers might warm themselves

This is the third way we’ve discovered that flowers might warm their immediate environment. They also do this in two other very cool things:

1. Absorb sunlight (through their shape, color, or physically moving with the sun)

2. A science fiction-sounding ability called thermogenesis, where flowers essentially make their mitochondria breathe real fast to generate heat. Eastern skunk cabbage uses this to physically melt snow when it comes up in early spring.

These techniques aren’t available to all flowers. Helleborus foetidus, for example, lives in the understory, where there’s not that much light to absorb. The researchers say that “this suggests the intriguing possibility that in cool, shady forest environments,” yeast could substitute for direct sunlight. “Intriguing possibility” in a research paper is the equivalent of a regular person grasping you by the shoulders, pointing at something, and screaming, “Isn’t that so cool?!”

The reason they think it’s so cool is that it suggests a variety of “ecological consequences.” (Heavy emphasis on suggests, which will become very important in the next section.) For example, other studies have shown that warmer flowers help plants reproduce for a variety of reasons, including:

• Increasing pollinator visits. A warm flower is a nice treat for a bee on a cold day.

• Bluntly, makes plant sex work better. Pollen grains have an easier time doing all the things they need to do once they land on a stigma—germinating, growing a tube, fertilizing an egg

• Helps fruit develop

• Makes bigger seeds

In other words, if you’re a flower, finding a way to raise the temperature makes it more likely that you’ll reproduce successfully. A person looking to find a mate might dress nicely, work out, go to therapy, get a good job and a stable life. A flower might host nectarivorous yeasts. We’re not so different, right?

They do note a major potential tradeoff, though. Yeast warm means yeast physically eating the sugar in your nectar. Bumble bees might not like a warmer flower if it doesn’t have much sugar left. They might choose a cooler but sweeter site instead.

Follow-up research: “Howevers” and “Well, actually’s”

This paper proved that yeasts do make flowers warmer. And so, as you might imagine, Herrera and Pozo next wanted to learn if yeasts actually did contribute to better flower production. That’s what they focused on in their 2013 follow-up study.

In a jarring second-act turn, they reported that yeasty flowers did attract more bumble bees, but at the cost of reproduction. This was because yeasts ate so much of the nectar that they actually harmed flower reproductive activities. That is, they were sort of like a reverse aphrodisiac. Not good wingmen.

But other research complicates the picture further. Vannette, Gauthier, and Fukami (2013) found that bacteria, and not yeast, negatively affected flower fertility. This line of research really messes with my “throuple” and “love triangle” framing, since it points out that this is a complex system with lots of moving parts and actors.

And then in 2017, Herrera, this time with another researcher named Mónica Medrano, studied if the heat effects alone were beneficial. That is, they separated the Yeast Eating All The Sugar variable from the Nice Warm Flower variable. They found early-blooming plants benefitted reproductively, but late-blooming plants suffered. One reason for this might be that bumble bees like a warmer flower when it’s cold out, but they don’t when it’s warm out.

Where this leaves us

The story of this ecological love triangle turns out to be a messy, complex relationship between more species than we commonly think. Intuitively, the presence of yeasts in hellebore nectar should be a net positive for everybody involved in this story. If it wasn’t, evolution would’ve put a stop to it one way or another.

But the results of these studies don’t let us say, “What a nice, mutually beneficial relationship! Representatives from three of the kingdoms collaborating and cooperating.” Instead, we have an image that’s as fuzzy as a buff-tailed bumble bee’s butt: a relationship that’s sometimes beneficial, sometimes harmful, and where none of the actors is fully in control.

Northern spicebush is a fairly large shrub, up to 12 feet tall and 12 feet wide. It’s shorter and bushier if it gets a lot of sun.

It’s one of the first bloomers each spring and has striking little yellow flower clusters. When crushed, they smell a little like crushed allspice and lemon zest.

The bright yellow spring flowers are also why this plant sometimes appears on replace-these-plants-with-native-alternatives lists as a forsythia substitute. Bluntly, forsythia in spring is stunning, almost sickeningly so. It has the mass appeal of grocery store buttercream. Spicebush is more a smattering of bright yellow. Think fancy-bakery-oatmeal-raisin-cookie situation. We can still make a popular appeal for spicebush over forsythia, but not on blooms alone.

The leaves also smell like a kitchen that’s been baked in, spicy and citrusy. They turn yellow in fall. Leaves alternate along branches (they’re not directly opposite one another). They’re simple, widest in or just past the middle, with smooth edges. If you ask a child to draw a leaf, you might very well get something that looks like a spicebush leaf.

Flora of North America calls the leaves obovate, which means they’re narrowest at the base. Imagine an egg with the pointy end attached to the stem. That’s obovate.

However, the leaves often have pointy tips, which just makes them look like both ends are equally narrow.

Spicebush bark has very noticeable white, oval-shaped lenticels. Lenticels are pores that let bark breathe.

Plants with female flowers (that get pollinated) make little red fruits. Botanically, these are drupes, or fleshy fruits containing exactly one seed. They’re slightly oblong. These are typical laurel family (Lauraceae) fruits.

Where it lives

Habitat

Lindera benzoin likes the wet, rich soil of deciduous forests (made up of trees that drop their leaves for the winter). Apparently, early land surveyors used it as an indicator of good farmland.

As an understory shrub (that is, living under the canopy of trees), it can handle shade. One study found it may gather a lot of its light energy in the early spring, before the trees leaf out. That said, it does well in sun, too, dedicating more energy to leaves and less to height and branching.

It likes to be near streams, swamps, and various waterways, more so than most understory shrubs. If spicebush were a person, it would want to sit in a folding chair in the shade by a creek. Maybe work on its paintings or fish.

A lot of sources mentioned that it often grows near tulip tree (Liriodendron tulipfera). They don’t depend on one another or anything; they just like the same conditions. This is a useful indicator for gardeners, since if you have one you could also potentially plant the other.

Native range

Spicebush is native across most of the eastern half of the U.S. Its range extends up into Canada (southern Ontario) and down through Texas.

Who it feeds and shelters

Pollinators

Lindera benzoin is an early bloomer with small, easy-to-access flowers that are enjoyed by early emerging bees and flies. These include:

• Mining bees (Andrena genus)

• Sweat bees (Halictidae family)

• Plasterer or cellophane bees (Colletes genus)

• Hover or flower flies (Syrphidae family)

• Bee flies (Bombyliidae family)

If you’re not an insects person, this list may just be a name dump. So here are a couple tidbits.

• A single margined calligrapher fly larva (Toxomerus marginatus) eats literally hundreds of aphids before it pupates (that is, turns into an adult).

• Andrena erigeniae, the spring beauty mining bee, nectars on spicebush, but will only eat pollen from spring beauty (Claytonia virginica). When she does this, she gets coated in pink fluffy pollen and appears to be wearing pink pants.

As a host plant

Among plant nerds, this species is probably most famous for being chomped on by swallowtail butterflies (Papilio genus). The adult spicebush swallowtail (Papilio troilus) is traffic-stoppingly stunning—and so is the caterpillar, in its own way. The latter has these large fake “eyes” that are intended to make it look like a little snake, warding off birds and other predators.

Lindera benzoin also hosts the eastern tiger swallowtail (Papilio glaucus, also a looker) and in the southeast of its range, the Palamedes or Laurel swallowtail (Papilio palamedes, also striking).

Because the butterflies are so impressive, you hear less about another lepidoptera that develops on this plant: the promethea silkmoth (Callosamia promethea). Their cocoons hang on the plant all winter.

The HOSTS database lists 16 butterflies and moths that use northern spicebush as a host plant. It may also host other insects, such as the sassafras borer beetle, but other insects don’t get as much attention as butterflies and moths.

Finally, like other understory shrubs, this one provides critical shelter for birds and small mammals.

Birds and mammals like the fruit and leaves

Spicebush fruit contains a lot of fat, which makes it a great energy source for birds, especially migratory ones. Wood thrushes are often cited as associated with spicebush, perhaps because they use it for shelter in addition to food. A recent 3-year study observed 24 species of birds feeding on spicebush. Each season, the most common visitor was Swainson’s thrush. Brown thrashers, American robin, and northern cardinals were also frequent visitors.

Mammals will also eat the berries, including eastern cottontail rabbits, raccoons, and opossums. There’s some debate about if deer will browse the leaves; I imagine it comes down to how desperate (and overpopulated) the deer are.

How it spreads

Spreads through cloning itself through its roots and by seed.

Spicebush can send out roots laterally. These produce adventitious buds—which basically means “a bud in a weird place”—that send up new stems. Each new stem becomes a new spicebush. Over time, you get big colonies of the shrub. Members of the colonies are clones of the parents that spawned them.

To editorialize for a moment: this is a weird strategy for a plant that keeps male and female flowers on separate plants (dioecious). Each clone is the same sex as its parent, so you can get big colonies of only males or only females. It has to make spicy plant love to make seeds.

This is relevant if you want to grow spicebush. You’ll only get fruit if you have a male and a female plant, and you can’t tell until they flower (three or more years in). So you likely need to plant a few and hope you get both sexes.

When it does produce seeds, it spreads in the usual way: bird eats berry, poops out seed, seed sprouts, etc. This other way of spreading helps spicebush colonize new sites. It also provides genetic diversity, since cloning involves making an exact copy of the parent.

Spicebush seeds die if they dry out. The botanical word for this is recalcitrant. This means if you purchase spicebush seeds, you need to keep them in moist sand (or something similar) to keep them viable. In nature, they rely on the moisture in the soil of their preferred environments.

How people have used it

As its name suggests, spicebush has a history of being used in cooking. During the revolutionary war, colonists used the fruits as a substitute for allspice. They may also have learned from the Cherokee that it could be used for tea, along with flavoring various dishes.

Native peoples used this plant for medicinal reasons as varied as treating colds, measles, and to induce sweating (that is, as a diaphoretic).

Plants in Plain Language is free. Subscribe to get fun and plant nerdery in your inbox.

You can also help me rationalize spending even more time on this—writing, researching, trying to get photos of very spontaneous bees—by buying me a coffee or becoming a monthly sponsor.

Sources this is from

• HOSTS - a Database of the World’s Lepidopteran Hostplants

• Lindera benzoin | Flora of North America

• Lindera benzoin | Flora of the Southeastern US

• A model of patch dynamics, seed dispersal, and sex ratio in the dioecious shrub Lindera benzoin | Journal of Ecology

• Northern Spicebush (Lindera benzoin) | bplant.org

• Northern Spicebush, A Great Shrub for Birds (and More) | North Carolina Native Plant Society

• Search for spicebush | BRIT, Native American Ethnobotany Database

• Spice Up Your Garden with Spicebush | Penn State

• Spicebush | Outdoor Learning Lab

• Spicebush | USDA

• Spicebush | Holden Arboreum (has a cool diagram of the leaves and fruit)

• Phenoseasonal subcanopy light dynamics and the effects on Lindera benzoin | PMC

• Use of northern spicebush (Lindera benzoin) berries by birds and mammals in Southern Appalachia | T&F

Rules like these are meant to help us wait until it’s warm enough for tomatoes to do well outside. But what about in years like this one, where it’s past the threshold, but still 40°F at night? Can I risk putting them out a little early? The Tomato Shuffle, where you run them outside during the day and then back to the grow lights at night, gets tedious pretty quickly.

A 2024 paper, “Recent Insights into the Physio-Biochemical and Molecular Mechanisms of Low Temperature Stress in Tomato” (Kwanuk Lee and Hunseung Kang in the journal Plants) reviews the main things we know about how cold affects tomatoes. In this piece, I’m going to summarize in plain language the parts of the paper that are relevant to home gardeners. This helps us understand when to plant tomatoes outside with a little more nuance than a calendar milestone does.

But first: what counts as “low temperature”?

Unfortunately, the one thing this paper doesn’t do is define low temperature. I’ve heard that 50°F (10°C) is too cold. Other sources suggest 65°F (18°C) or more. Depending on where you live, this could mean waiting quite a while, since soil temperatures rise more slowly than air temperatures, and cold roots are at least as bad as cold leaves for tomato plants.

A 1993 study described germinating plants at 77°F (25°C) and then studied what happens to different plants if you reduce the temperature to 64°, 59°, and 54°F (18°, 15°, and 12°C). They found that the 64° group grew significantly better than the 54° group. However, plants in the 54° group didn’t stop growing; they just grew more slowly. So the takeaway here is that tomato growth slows near 50°F and accelerates as you move toward its ideal temperature of around 80°F (27°C).

The home gardener in a not-warm place needs to be practical; cold does set tomatoes back, but you probably don’t want to wait until June to start hardening your plants, let alone transplanting.

I’m going to continue using 50°F (10°C) as the threshold for when plants begin to feel the effects of cold damage. But if you live in a warm place, you can choose a higher threshold. Anyway, here are some things the Lee and Kang paper describe going wrong for tomatoes when it’s cold.

Tomatoes germinate and grow poorly in cold

Cold can delay and even prevent tomato seeds from germinating. Tomato plant cells also divide more slowly in the cold, i.e. they grow more slowly. This is one reason we typically start them inside: it lets them get going faster and avoid unseasonably warm spring days that might trick them into germinating early.

Cold causes tomato plants to produce smaller, thicker leaves they would if it were warm. This is good for survival, but bad for things like photosynthesis. Mature plants produce fewer flowers (and thus fruits) in cold weather.

Less chlorophyll (the molecule that allows plants to absorb light)

Cold-stressed plants make less chlorophyll while they are cold. Chlorophyll is a molecule that absorbs mostly blue and red light so that plants can convert it to energy. As an aside, this is one reason plants appear green. They’re absorbing red and blue light and reflecting green light. Kind of ironic; we see the light they’re rejecting, not the light they need. Anyway, less chlorophyll means less light absorbed. Less light absorbed means less energy to use on what you want to slice up and put in a sandwich.

Cold damages plant cells, which causes them to lose water and nutrients

Plant scientists use an indicator called electrolyte leakage to identify when a plant’s cells are damaged. A paper that describes how to measure electrolyte leakage explains it this way:

When a cell dies and loses the integrity of the cell membrane, electrolytes, such as K+ ions, leak out of the cell. Thus, we can use the amount of electrolytes leaked from a tissue as a proxy for the extent of cell death in the tissue.

In other words, when tomato plants get cold, cell membranes can’t do their jobs. They leak electrolytes and water. Seems bad.

Antioxidant defenses don’t work as well

Molecules that are reactive can cause a lot of trouble in bodies. You’ve likely heard the terms “free radicals” and “antioxidants” in the context of human nutrition. Plants also have these.

Free radicals are molecules with an unpaired electron. They badly “want” to pair this electron and will “take” one from another molecule. Antioxidants provide these extra electrons, which prevent free radicals from taking them from things whose stability you don’t really want messed with, such as DNA molecules.

Scientists can measure the concentration of oxygen-containing free radicals, along with reactive molecules that contain oxygen. They call these reactive oxygen species, or ROS. A small number of ROS is useful, helping plants respond to various types of stress. But lots of ROS are bad. You don’t want lots of desperate molecules zipping around your tomatoes’ bodies, stealing electrons. Chaos ensues.

Plants make enzymes that “scavenge” for reactive oxygen species. This helps keep ROS numbers manageable. However, in low temperatures, these enzymes are less active. This leads to higher, more toxic numbers of reactive molecules in the plant. It’s not technically correct to say that cold might “give tomatoes cancer,” but if that helps you remember this dynamic, I say go for it.

Fruits taste worse

You already know about this if you’ve purchased a tomato at the grocery store. Tomatoes are often stored cold to make them last longer. However, doing this makes them taste worse. This happens because when chilled, tomatoes lose volatiles, the chemical compounds responsible for flavor.

I can think of a few scenarios where cold fruit is relevant for home gardeners.

• If you know it’s going to get cold when tomatoes are ripening, you may want to cover your plants to protect them (row covers, blanket, etc.)

• If you pick tomatoes early to let them ripen indoors, don’t refrigerate them. You’d basically be simulating a cold night.

• I always have a few tomatoes hanging on the vine when it starts to get cold in the fall. In the future, I’ll pick any of these with any blush and let them finish indoors.

Conclusions

This isn’t everything that can go wrong for tomatoes in the cold. For example, a study that focused on cold soil temperatures also showed that plants with cold roots don’t photosynthesize as well. However, it’s enough for home gardeners to know that cold will set your tomatoes back significantly.

The major takeaway from this is, we need sustained, warmer air temperatures in spring to bring soil temperatures up. This year, for example, with temperatures still dropping into the low 40s, I’m still not quite ready to plant tomatoes outside, even if Mother’s Day’s already come and gone.

You can check soil temperature with a soil or compost thermometer. They cost less than $10 in a variety of places; just make sure it’s long enough to get down into the root zone.

A related takeaway is that many tricks people use to plant earlier protect from cold air, but not cold soil. For example, row covers warm the air beneath them but have less of an effect on the root zone. Straw and wood chip mulches might actually prevent soil from warming up in the spring, since they block sunlight. And I once saw someone set dozens of tealights on their raised bed, which looked pretty, but probably didn’t do much for the roots.

Finally, the paper I summarized is about tomatoes, but it’s safe to assume that other “warm-season” crops, like peppers and cucumbers, have similar biological challenges. As much as those of us who live in cooler places want to start our gardens’ engines this time of year, it’s best to wait until our weather is a good fit for our plants.

Sources

• Recent Insights into the Physio-Biochemical and Molecular Mechanisms of Low Temperature Stress in Tomato | MDPI (This is the paper I was summarizing)

• Effect of low root-zone temperature on photosynthesis, root structure and mineral element absorption of tomato seedlings | ScienceDirect

• Let soil temperature guide you when planting vegetables | Oregon State University

• Development of the Fifth Leaf is Indicative for Whole Plant Performance at Low Temperature in Tomato | ScienceDirect

• Quantification of Plant Cell Death by Electrolyte Leakage Assay | PMC

• Tomato Fruit Volatiles | van der Knaap Lab

• Reactive oxygen species generation and signaling in plants | PMC

Plants in Plain Language is free. You can subscribe for weekly fun and plant nerdery in your inbox.

You can also help me rationalize spending even more time on this—writing, researching, trying to get photos of very spontaneous bees—by buying me a coffee or becoming a monthly sponsor.

But—and I acknowledge it’s kind of an annoying “but”—this is only part of the story of what bees, as a group, love. Garden variety observing (as well as professional observing, it turns out!) is shaped by a kind of informal detection bias. That is, when things are easy to observe, we’re more likely to observe them—and then those observations are more likely to structure the story we tell.

I want to poke at the typical story of what bees love, not to be provocative or irksome, but because I think there’s a better one. Among other things, it gives us an excuse to buy more plants.

The visibility bias

The most obvious explanation for bees loving something is not the flower, it’s the type of bee. Some bees just make it easy to see what they’re doing.

For example, honeybees tend to forage as a colony, and those colonies are notably huge. A honeybee scout can “tell” its hivemates about a patch of flowers, which results in lots of bees showing up. Quite noticeable from a human perspective!

Bumblebee colonies are much smaller, but they are still colonies, sometimes made up of hundreds of bees. And bumblebees tend to be quite large and conspicuous and bumbley. Four or five bumbles feels like a lot of bee.

By comparison, imagine you are an unequal cellophane bee (Colletes inaequalis). You’re solitary (though you do build neighborhoods of nests, or aggregations). You emerge in early spring, you head for the few restaurants that are open, such as maples, willows, serviceberries. These tend to be kind of far off the ground, but you don’t mind. You can fly, after all. You are not so likely to be observed by a gardener up there, but that’s not really something you think about.

If you’re male, you die after just a few weeks. If female, you maybe get a month and a half. Your larvae are tucked underground, sealed off and protected until they’re ready to emerge. The gardens in your neighborhood are still waking up, the gardeners inside and staring impatiently out their windows.

About 90% of our native North American bee species are solitary. That means Colletes inaequalis is one of about 3,600 species that are easy to leave out of a story about what bees love.

The horticulture bias

Imagine you are a spring beauty mining bee (Andrena erigeniae). Like about 25% of bee species in eastern North America, you specialize on a particular plant. You only forage pollen on spring beauty (Claytonia virginica or C. caroliniana), and when you do, you end up with pink pants.

You don’t really visit many gardens. You’ll take nectar from most flowers, but your larvae need pollen specifically from spring beauty. Most people don’t plant these. You Spoke With The Manager at the local plant nursery about this, but she shook her head. “Spring beauty is a short bloomer and it’s hard to maintain in pots. Plus, people just think tulips are prettier.”

So you’re not in gardens. You’re in an eastern deciduous forest on a flower smaller than a dime. People tend not to see you on plants in their yard, and thus rarely mean you when they say that bees love something.

The on-the-menu bias

Imagine you are a honeybee. You have five eyes. You’re looking for food, and you fly over a suburban lawn. There’s grass, dandelions, and clover. Clover’s pretty good. You like clover. You evolved to eat its pollen. You’re both from the same regions of Europe and Asia.

Dandelions are okay. You don’t actually love dandelions. Not enough nectar, pollen not filling. But it’s better than grass, which is notoriously short on nectar and pollen.

All things considered, you’re notoriously not a picky pollinator, but this restaurant’s kind of mediocre. There are plenty of flowers in North America you like, but they’re not common here in the suburbs. What there mostly is is grass. So much grass.

You and your hivemates get to work on the clover. From a few feet above, someone snaps a picture. “You guys really love this clover,” they say.

The I-can’t-see-the-future bias

One last bias, which is better illustrated with butterflies than bees, though the same principle applies.

Imagine you are a gardener, and you have a butterfly bush (Buddleia davidii). It’s covered with butterflies. It has large, obscene clusters of flowers with nectar that’s easy to get to. The butterflies love it!

You have an annoying neighbor, a Well Actually type. Well Actually says butterfly bush doesn’t host any butterflies. He says they only lay eggs on plants their larvae can eat.

Well Actually also whines about how butterfly bush can escape the garden and form colonies along riversides and displace critical native plants. Well Actually says butterfly bush is actually illegal to sell in many states now. It’d be better to put in something like buttonbush or viburnum or summersweet.

You’re sad to learn when you look it up that most of this is true. But it makes no sense! Look how many butterflies are on this plant! You can see with your own eyes that they must like it!

Things bees love that are harder to see

So what should the aspiring-to-support-wildlife gardener do besides look?

First, continue to be delighted when things are covered with bees. Bees are cool garden companions. But here are a few other chapters to add to the story.

Plants that bloom for a long time and have small flowers

Plants that bloom for a long time and have lots of small flowers are generally bee friendly. Mountain mint is a good example. Most mountain mints have hundreds of flowers packed into little clusters. They produce them continuously for weeks. The nectar’s easy to get to because the flowers don’t have long tubes. And they bloom in late summer, which I think for many of us fills a gap between our summer bloomers and fall bloomers.

The Xerces society has lists of pollinator plants for every region in the U.S. that include bloom time, among other things.

Blooms all season

Here’s a new excuse to buy more plants: you want things blooming all year long. If your garden absolutely explodes in summer but has fewer things in fall, add fall bloomers. Same with spring. Bees need resources as long as they’re active.

Add native plants

Many native solitary bees have relationships with the plants they evolved with. You can even choose plants “backwards”: find a native bee or moth that lives near you, learn what it eats (or what its larvae eat), and plant it, preferably in a “drift” or large group.

Let the story include more than just bees

There are lots of things beyond bees that are a little harder to see, but which we should still colloquially include in “bees love it.” Hoverflies look like bees to deter predators. Sometimes their larvae even feed on aphids. Wasps are fantastic predators of the insects in your vegetable garden. And moths, even the dull-looking ones, represent a critical food source for most birds (i.e. moth caterpillars). Many of these will feed on the same flowers you’re planting for bees.

Plants in Plain Language is free. You can subscribe for weekly fun and plant nerdery in your inbox.

You can also help me rationalize spending even more time on this—writing, researching, trying to get photos of very spontaneous bees—by buying me a coffee or becoming a monthly sponsor.

This family has been frustrating taxonomists—people who study how to describe and classify things—for centuries. It contains between 2,500 to 4,000, depending on who’s counting. This makes it a fairly large family.

Species in this family that you might know

• Strawberries (Fragaria species)

• Hawthorns (Crataegus spp.)

• Blackberries (Rubus spp.)

• Cherry and plum trees (Prunus spp.)

• Apples (Malus spp.)

• Spiraea (Spiraea spp.)

• Serviceberry (Amelanchier spp.)

• Roses (Rosa spp.)

Defining characteristics

The flower arose from a cup! The hypanthium

A defining rose family feature is a structure at the base of flowers that’s made from fused flower parts: petals, sepals, and stamens. The structure, the hypanthium, is frequently described as cup-shaped. It contains the ovary, the female reproductive part of the flower.

A more familiar image might be a pear. If you cut a pear in half the long way, the core (with the seeds) is the ovary, and most of the pear’s flesh is hypanthium tissue. Apples, too.

So for “cup-shaped” to be useful, we need a pretty broad definition of cup. Urn, vase, goblet, etc. Flowers in this family arise—or arose, if the mnemonic helps—from these structures.

Other families’ flowers also have hypanthiums. You’d use this in combination with other features to make an ID.

Flowers

Rosaceae flowers usually have five petals and five sepals, or leaf-like structures at the base of the flower. Flowers are radially symmetrical, which means you can divide them in equal halves in multiple ways. They have whorls of stamens (the male part of the flower, which look like tiny shoots) around their interior.

A “gotcha”: Sepals and bracts

Some plants, such as strawberries, cinquefoils, and avens, have five sepals and five (or more) bracts, or leaflike structures, that make up the part of the flower that protects the petals. I’d like to shout from evolution’s peanut gallery that these are sometimes difficult to tell apart. For example, on Virginia strawberry, you’ll see what seems like a whorl of ten green leaflike “things.” These are sepals and bracts. The sepals are broader, the bracts narrower.

Another “gotcha”: Rose vs. buttercup family flowers

The buttercup family (Ranunculaceae) features a few plants that might appear like rose family plants. For example, plants in this family have open flowers with lots of stamens, and many appear to have five petals. (Often the petals are actually sepals, but you wouldn’t know just from looking.)

However, buttercup family plants don’t have the hypanthium or stipules. Buttercup flowers also tend to have sepals colored like their petals.

Alternate leaves with stipules (an almost-leaf at the base of the leaf stalk)

One useful identifying feature for this family are little leaf-like growths, or stipules, at the base of the leaf stalk (petiole). Sometimes this looks like a leaf that didn’t quite get going, and other times it’s more like little wings on both sides of the petiole. Stipules are prominent in roses, strawberries, and blackberries.

Unfortunately, and confusingly, stipules also can be subtle or fall off entirely, especially on mature foliage. Stipules that fall off as leaves develop are called caducous. This is common in black cherry (Prunus serotina), apples (Malus spp.), and pears (Pyrus spp.), among others

The vast majority of rose family plants also have alternate leaves, where leaves alternate up the stem instead of being across from one another (which would be opposite).

Many species have compound leaves, where a leaf is actually made up of stems and leaflets. What this means for an aspiring identifier is that leaflets might appear opposite, but leaves—the whole structure with leaflets and their stems—are usually alternate. Unfortunately, leaflets look almost exactly like leaves. Botanists distinguish them based on the placement of buds, or shoots that haven’t developed yet. Leaflets don’t have buds, while leaves have them at their base.

Most rose family leaves are also serrated, or have “teeth,” like a saw.

Taxonomists are still working on classifying this family

There’s quite a lot of debate on how many species this family contains. The genus Rubus, for example (blackberries, raspberries, dewberries, etc.) contains either hundreds or thousands of species. There’s no consensus. Crataegus, Hawthorns, have somewhere between 200 and 1000 species.

As an illustration, I submit this exchange about Himalayan blackberry identification from iNaturalist’s forum. One commenter, Dr. Barbara L. Wilson, offers this very clear explanation for the confusion (emphasis mine):

Here’s the problem with the European Blackberry Complex…Members of the European Blackberry Complex reproduce in a way that really messes with our species concepts. They mostly set seed asexually. What seem to be distinct individuals are actually clones, and a single clone might cover a whole county or more.

However, blackberries also have sex. They may have sex even with distantly related members of the complex. The offspring of such crosses can look a bit different from the blackberry clones that were already spreading around the area. Are these clonal populations best thought of as different species or just different genetic individuals? How different do they have to be before we name them? Should every slightly different type be called a species? (Some people would argue yes, which is why you have 2000 named dandelion species in Europe.) If not, how much difference is necessary to name a species? This really messes with biologists’ minds. We don’t agree. We probably will never agree.

Value for wildlife

Pollinator plants

In general, Rosaceae is one of the most important families for pollinators. First, they tend to bloom in spring, and prolifically, when few other things are in bloom.

Humans aren’t the only ones that enjoy cherry blossoms. Plants like black cherry, serviceberry, hawthorn, and strawberries are critical, early sources of pollen and nectar.

Rose family flowers are open. You don’t need a long tongue or beak or proboscis (tube-like feeding structure some pollinators use to access nectar, sort of like you had a straw for a mouth) to gather from a rose flower. They’re accessible for all sorts of small insects, including bees, hoverflies, beetles, moths, and butterflies. They’re sort of like a big box store for pollinators.

For food and shelter

Rose family fruits feed all sorts of birds and mammals–including humans. For example, here in the forests of the U.S. northeast, black cherry (Prunus serotina) is a pillar of the ecosystem. Its fruits are eaten by dozens of birds, including robins, cedar waxwings, and wild turkeys, as well as by mammals like foxes, bears, and raccoons.

This is also a critical host family for butterflies and moths, and therefore by extension, animals that eat caterpillars. The Prunus genus, made up of cherries and plums, ranks among the most important supporters of native northeastern caterpillars—that is, either potential moths and butterflies or potential food for birds, depending on your perspective.

Hundreds of butterflies and moths specialize on plants in the Rosa genus (that is, actual rose plants). Virginia strawberry (Fragaria virginiana) is a fantastic caterpillar host in groundcover form, supporting something like 75 species.

Value to humans

Like animals, we’re big fans of eating this family. For example, we grew 23.1 million metric tons of pears in 2020. Other Rosaceae fruits are nearly as popular: apples, strawberries, peaches, blackberries, and so on. Almonds are part of this family, too. We use rose hips for tea and in cooking or baking.

People have a long history of using plants in this family medicinally and still do today. Rose hips are a good source of vitamin C and were even used in Britain during World War 2 when citrus was in short supply. Hawthorn has been used historically in both Europe and China to treat heart conditions. The family member I’ve named several times already, black cherry, has been used to treat coughs. Rose oils, particularly the essential oil attar of roses, are used in perfumes.

One more mention of black cherry, Prunus serotina here. It’s often used for lumber, especially furniture and paneling, because of its red finish.

Okay, let’s talk about (actual) roses

A fact so obvious it’s almost not worth writing is that we like to put plants in this family in our garden and look at them. We appear to have climbed down from the trees and immediately, evolutionarily speaking, begun cultivating roses. There’s evidence that people in China were cultivating roses 5,000 years ago. But the features we breed for today, such as doubled petals, tend to come at the cost of pollen, nectar, and hips. That is, we breed out the stuff that wildlife depends on.

It’s unfortunate that cultivating something aesthetically beautiful costs something ecologically beautiful. Our symbol of beauty’s a bumblebee’s boarded-up storefront.

But I’d like to think combining these perspectives gives us something even nicer. Wild rose flowers are amazing. And then you can slide in the lens that helps you imagine the birds, moths, and bees they sustain. That’s a plant that blows back one’s proverbial hair. And if my wife reads this far, some men do like roses for anniversaries, so long as they’re plantable and wild type.

Sources

• Bringing Nature Home, Doug Tallamy (2007)

• Chapter 8. Rosaceae: The rose family | UC Riverside

• Evolution of Rosaceae Fruit Types Based on Nuclear Phylogeny | Molecular Biology and Evolution | Oxford Academic

• Identification of Roses, Leaf stipules | Violets and others

• Families-Rosaceae | Ohio Plants

• Himalayan Blackberry Confusion | iNaturalist Community Forum

• Rosaceae | Purdue Horticulture & Landscape Architecture

• Rosaceae lecture | Ohio Plants Online, YouTube

• Stipule | Master Gardeners of Northern Virginia

• Stable temperatures

• No wind (unless you point a fan at them)

• Much less intense light

• Fewer pests

• Regular watering

Under these conditions, plants skimp on cell walls. They skimp on stem length. Leaves don’t bother with the waxy coating, or cuticle, that protects them from very bright light. And thus Mike Birbiglia’s observation about indoor cats also applies to the plants we start indoors.

Before we take indoor-started seedlings out to the vegetable garden, we need to acclimate them to what it’s like out there. Plants have the incredible capacity to morph their physiologies in response to environmental conditions. Sort of like if you could force grow a fur coat each winter. The fun technical term for this is thigmomorphogenesis, coined by M. J. Jaffe in a 1973 paper describing how some plants respond if you rub their stems.

The hardening process

Hardening, or hardening off, refers to plants getting literally harder and sturdier. We put them through a sort of plant boot camp.

This transition generally takes about two weeks for seedlings. (Houseplants may appreciate more time, since they’ve been inside for months, not a few weeks.)

I’ll give two processes, which you can think of as defining a spectrum from “cautious to the point of micromangerial” to “I don’t have time for this.”

The micromanagey process

• Days 1-3: Leave seedlings in a shady spot for an hour or two, then bring them back inside. Important: Shade outdoors is more intense than most grow light setups. You’re already exposing them to more light than they’ve been getting inside.

• Days 4-7: Introduce morning light, which is less intense than afternoon light, and increase the total time they’re outside. Move them back to the shady spot in the afternoon. Leave them outside longer each day, too. By the end of the week, they can be out for most of the day.

• Day 8-10: Include afternoon sun.

• Day 11-14: Put them out earlier and leave them out later so they get used to cooler night temperatures.

The “I don’t have time for this” process

• Day 1-7: Find a spot that gets a few hours of morning sun and is shaded all afternoon. If you don’t have that, find a spot that’s shady all day. Leave them there during the day and bring them in at night

• Day 8-14: Don’t bring them in at night unless it’s going to be below 50 degrees.

Obviously, you could put them in the ground on day 8 with this method. The only reason I suggest leaving them in pots is because we tend to time things so that they go into the garden at the earliest possible, and therefore just-barely-warmest, time. The extra week in pots gives you a little flexibility. If you get an unexpected cold night, you can still bring them in.

A number of caveats and nuances

Location, location, etc.

Choose location(s) that help you manage all the various environmental factors seedlings will be exposed to.

• Morning sun is less intense

• Afternoon sun is more intense

• Outdoor shade is often brighter than under your indoor grow lights

• You would likely prefer that rabbits or squirrels not have easy access to them

• Wind can be very damaging for tender, unhardened seedlings

Light intensity

It’s useful for us to understand a skosh about light in different contexts: grow lights, outdoor shade, outdoor direct sun. You’ll see light measured in a few different ways. There’s “foot candles,” which is essentially how many candles’ worth of brightness something is. Scientists might measure light in µmol/m²/s¹, or micromoles per square meter per second, or how much light is available for photosynthesis.

But since most of us aren’t measuring light, what’s important is that the shade under your oak tree is usually brighter than your grow lights. This is because the atmosphere diffuses sunlight—that is, scatters it, and quite vigorously—into shady spots. And while it’s counter intuitive, the amount of light being scattered into the shade is much brighter than the amount produced by grow lights.

Watering and rain

You may need to water more often outdoors. Wind and sun tend to dry plants out more than sitting on a shelf with a grow light.

Rain is fine if it’s light. If it’s going to rain a lot, bring seedlings inside. Plants in small containers can easily get waterlogged and even physically damaged. Remember, they haven’t finished thigmomorphing yet. A downpour can crush weak stems.

Don’t water if they don’t need it. Stick your finger into the growing medium and check for moisture just below the surface.

Look out for signs that you’re pushing seedlings too hard

The most common sign that plants aren’t ready for the amount of light they’re getting is white spots on leaves. The leaves may turn light gray or white (bleaching). You can certainly kill seedlings this way if you’re not careful.

Some leaves may develop red, purplish, or orangey colors. This is fine. These pigments (flavonoids) protect plants from too much light. The most recognizable of these are likely anthocyanins, which cause the reddish color that the leaves of pepper seedlings often take on, even indoors.

When is it time to harden off plants?

1. When your seedlings are ready

2. When the conditions outdoors are ready

The general rule is to wait until seedlings have at least 2 sets of true leaves. That is, not the first leaves, or cotyledons, that emerge. We want the next sets, which look like the plant’s mature leaves.

But the conditions outdoors have to meet the plant’s minimum requirements. You can’t start zinnias indoors and then try to harden them in April in New England. Zinnias like warm weather and won’t be thrilled about nights that might still drop into the thirties.

It helps to know your last frost date. But more than that, it helps to have done some research about what your plant will tolerate. Some plants tolerate cold. Others need nighttime temperatures over 50°F / 10°C.

Some plants are better off started outside

For example, you can generally put in peas and onions as soon as you can manipulate your soil. That lets you skip the entire hardening process. Root vegetables (carrots, parsnips, radishes) tend to do better planted directly, since they react poorly to root disturbance.

Many cut flowers, even warm-season ones, have plenty of time to mature even if you wait and start them outdoors. This includes cosmos, zinnias, marigolds, sunflowers, and nasturtiums.

And I know one gardener who only starts zucchini in late July, after the squash borers have completed their life cycle.

Native plants are often best started from seed. One of the nicest things about native plants is that they evolved to grow in places with harsh winters. You can scatter them in fall or use one of the numerous guides to milk jug winter sowing. We generally harden things only when we need to create the right (artificial) conditions for something to grow where we live.

Bonus nerdery: What’s actually happening during hardening?

A few different things, some of which are quite visible. First, plants produce a waxy layer over their leaves (and green stems and fruits) called a cuticle. The cuticle is a critical adaptation to all sorts of environmental stresses, one of which is limiting the harmful effects ultraviolet radiation can have. For example, plants may reflect UV rays or absorb them in a way that prevents them from affecting tissue.

They also produce the flavonoids, including anthocyanins, that we mentioned earlier.

Plants harden their cell walls. They produce more lignin, the substance that makes wood woody. It functions a little like biological cement that fills in gaps between cellulose in cell walls. Imagine dunking a pillowcase in glue and letting it dry. That’s sort of what’s happening during hardening off to stems and leaves.

A few other things happen, too, including faster root growth and changes in energy storage and water use.

Like other members of the arum (Araceae) family such as peace lilies, it can burn carbohydrates stored in its roots to warm the air right above it as much as 20 degrees (thermogenesis). This allows it to melt its way up through still-frozen ground and move its bloom time to very early in the year.

It comes up flower first, leaves still furled spear-like. The hood (spathe) is a fleshy purple or maroon with green or white mottles. It protects the flower cluster (spadix). The appearance probably contributes to attracting early season flies, as does the smell, which one author apparently described as combining “skunk, putrid meat, and garlic.”

Native range and habitat

Native across the northeastern U.S., the upper midwestern states, and southern Canada. Extends south through North Carolina and a single sighting in South Carolina. It’s much rarer in the southern states, since it’s not adapted to hot summers. The northern U.S. and southern Canada also contain more of its natural habitats. See a range map on bplant.org.

Its habitats tend to have a lot of groundwater. It wants the wet muck of waterways, swamps, and seeps (places where groundwater naturally comes to the surface). It also grows in wet deciduous woodlands (that is, woodlands where trees drop their leaves). It’s even evolved so that its roots can physically contract, which helps it anchor itself into the soil. This force is strong enough to pull the entire stem beneath the ground.

These types of habitats, consistently moist and cool, are much more common in the northern part of its range. In the south, it’s likely limited to higher elevations, where it’s cooler and moister.

Prefers at most partial sun and tolerates fairly deep shade. Does not like direct sun.

Interactions with wildlife

Pollinators

As your resident goth forest plant denizen, eastern skunk cabbage is of course pollinated by things like flesh flies, carrion flies, carrion beetles, and gnats. Its, uh, “floral scent” includes compounds that make it smell like rotting protein to attract them.

Eastern skunk cabbage blooms when very few other things do, as early as February and March in some places. In addition, as we mentioned, it’s able to warm the air inside its hood. This means it provides food and shelter during a critical time of year, especially in the cold places where this plant is found.

Spiders sometimes build webs inside the spathe to take advantage of insects looking for a warm place to rest.

Host plant

Hosts a few species of moth, including the ruby tiger moth (Phragmatobia fuliginosa) and cattail borer moth (Bellura obliqua). These don’t specialize on eastern skunk cabbage, though. The ruby tiger moth is a generalist, and the cattail borer is more narrowly focused on wetland plants (such as cattails).

Mammals

Deters most mammals. Its leaves contain razor sharp calcium oxalate crystals, the same substance that makes up kidney stones. Eating it apparently causes a burning sensation in your mouth and throat, as well as vomiting and diarrhea.

Still, animals emerging from hibernation will eat it in desperation. Many sources mentioned black bears and snapping turtles eating it when there’s not much else around.

How to identify it

We’ve already touched on its flower structure. This has 2 major parts:

• The spathe is the hood that protects the flowers. (This is the same structure as the white hood on a peace lily.) On eastern skunk cabbage, it’s a mottled purple, like someone has only applied a single coat of paint.

• The spadix is a sort of fleshy-looking flower spike. The yellow flowers are small and don’t have petals

The whole flower structure is about half a foot tall, though the spadix itself is a few inches shorter. It blooms before its leaves unfurl.

The leaves come up with the flower structure, but they stay furled, spear-like, until late spring. They’re big, up to 2 feet long and a foot wide. They’re dark green, deeply veined, and look like cabbage leaves. Mature plants have four or more leaves per crown, immature ones fewer.

The petioles, or stalks that leaves attach to, are thick and stick out at an angle. The leaf structure forms what looks like a vase, and the plant really does look like a giant head of cabbage growing out of the ground.

By late summer, the leaves have withered away. At this point, the fruit is beginning to mature. It’s formed from the spadix. Each of the little flowers forms a small fruit, and they fuse together into a fleshy, lumpy mass, like something from a Tim Burton fever dream. The mass is ovular, dark purple to black, scaley-looking, and smells like rotting fruit. This compound fruit is called a syncarp.

How it spreads and grows

Reproduces only by seed. The syncarps we discussed rot and fall to the ground, allowing skunk cabbage to colonize areas. Floods may also disperse seeds.

Skunk cabbage lives for a long time (20+ years). However, it doesn’t handle when water systems are disturbed (e.g., by drainage). This makes it an indicator of if a wetland has a healthy hydrology.

Skunk cabbage isn’t technically spring ephemeral, since it doesn’t complete its aboveground lifecycle in the spring. It sort of rhymes with this way of growing, though, since it completes its bloom cycle very early in the year.

Uses by people

Lots of Native American peoples made use of skunk cabbage. As a food, it needed to be processed to be edible. For example, one report suggests that to eat them as vegetables, they had to be boiled, and the water changed at least 3 times during the process.

There are far more examples of its being used medicinally (not surprising, given that it may’ve been a pain to prepare, and even more painful to eat). Apparently both the Delaware and the Mohegans also used it for epilepsy. They may have passed this along to American doctors, who used it for this and to treat a few other diseases, including scurvy.

The roots were often dried and used to treat respiratory problems, such as coughs, colds, and tuberculosis.

Sources this is based on

• Skunk cabbage, Symplocarpus foetidus – Wisconsin Horticulture

• 7.2 Seeps | ‘Good Forestry in the Granite State: Recommended Voluntary Forest Management Practices for New Hampshire’

• Eastern Skunk Cabbage (Symplocarpus foetidus) - bplant.org

• Plant of the Week: Eastern skunk cabbage | USDA

• Skunk Cabbage (Symplocarpus foetidus)

• BRIT - Native American Ethnobotany Database

• Skunk Cabbage Flowers: The Heat is On

• Floral scent of eastern skunk cabbage (Symplocarpus foetidus: Araceae) - ScienceDirect

• Symplocarpus foetidus | Indiana Nature