IN THE AGE of local weather change, my visitor on as we speak’s reprise version of the podcast informed me, we are able to count on “extra poison ivy and meaner poison ivy,” and I’d say from what I see rising round me and the rashes on associates that each are coming true.
Although it could really feel prefer it to many gardeners and others who spend time open air, poison ivy was not placed on the planet to punish mankind for some sin—or to spice up antihistamine gross sales and dermatologist visits.
As with each native plant—and sure, Toxicodendron radicans is a local plant, and an necessary one at that—there may be methodology to what looks like insanity within the grand scheme of issues.
Poison ivy is likely one of the vegetation I’m requested about commonly by listeners, so as we speak we’ll get a a lot nearer look from a really secure distance, on this archived dialog with Dr. Susan Pell, and hopefully be taught what we have to handle round it higher, but in addition to present it the respect it deserves.
Dr. Pell is intimately accustomed to poison ivy and its kinfolk, as a result of she has for years studied them proper right down to the molecular stage. Dr. Pell is Govt Director on the historic United States Botanic Backyard in Washington, D.C., and likewise former director of science at Brooklyn Botanic Backyard.
On her Linked In profile, alongside all her spectacular scientific credentials: she additionally says this: that she “loves to indicate folks the coolness of vegetation.”
So maintain an open thoughts, gardeners, as we discover the “cool” of poison ivy—and naturally sensible, extra apparent issues like what to do to keep away from that rattling rash.
Learn alongside as you take heed to the Sept. 1, 2025 reprise version of my public-radio present and podcast utilizing the participant beneath. You’ll be able to subscribe to all future editions on Apple Podcasts or Spotify (and browse my archive of podcasts right here).
a poison-ivy q&a with dr. susan pell (reprise version)
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Q. Welcome, Dr. Susan Pell. Your space of analysis focus has been the cashew household [or Anacardiaceae], Susan, appropriate?
A. I research the evolution and variety of the cashew household, which incorporates poison ivy amongst its members, and pistachios, mangos, sumacs, smoke bushes—lots of vegetation gardeners are accustomed to.
Q. Smoke bushes, which means Cotinus?
A. Sure.
Q. That’s one I didn’t know was associated, or it had fled from my thoughts. Fascinating.
A. It’s truly fairly carefully associated to poison ivy.
Q. Now everybody: Don’t be afraid of your smoke bush!
A. Or sumac—besides poison sumac. The genus Rhus is completely fantastic.
Q. The members of the cashew household that almost all U.S. gardeners are conscious of are poison ivy and poison sumac—the place are their native ranges?
A. It type of depends upon the way you acknowledge the species of poison ivy. There are some very carefully associated species—I’ll name them sister species. In the event you embrace these below the widespread identify poison ivy, then poison ivy is present in each state within the U.S. aside from California. Though you do discover poison oak there—so that you get your share of the genus Toxicodendron there that approach.
The genus that causes the rash is Toxicodendron—which suggests “poison tree.” Poison ivy, poison oak and poison sumac are all species inside that genus. Frequent names are the place we get into the difficulty space, however within the strictest sense poison ivy is Toxicodendron radicans. It’s discovered from the Midwest to the Japanese United States.
However in the event you embrace different species, like T. rydbergii, and another species in that genus that every one get known as poison ivy, it extends in every single place in the US besides California.
Q. And which one does California have once more? I’m positive they don’t escape totally.
A. They’ve Toxicodendron diversilobum, poison oak, and it’s fairly nasty. The truth is, I’ve seen some reviews suggesting that 15 % of the State of California’s complete workmen’s comp finances is spent on poison oak-related absences and accidents, and that’s largely associated to firefighters. Folks combat the wild-land fires that California has, and there may be poison oak in it they usually’re inhaling that smoke. They are often within the hospital or out of labor for weeks.
Q. It’s one of many issues we’re warned about: In the event you do have particles from any of those vegetation, don’t burn it.
A. Right.
Q. What species is poison sumac [above]?
A. It’s Toxicodendron vernix. It’s discovered simply within the Japanese United States. Its vary is a bit more restricted than T. radicans; it happens from Texas and Louisiana eastward, nevertheless it doesn’t get deep into the Midwest (or into the West). It’s in moist and really swampy areas.
Q. My backyard is surrounded by state park. In two areas by the woodland edges I misplaced bushes final fall, and the situations modified. This spring, poison ivy has romped shortly in, prefer it was simply poised on the lookout for a possibility. It that its typical conduct—is it an opportunist?
A. It positively is. Poison ivy is what is known as a successional plant. It actually takes over in areas which have been newly cleared—say, by the constructing of a roadway, or possibly they’re repeatedly mowed, or in your state of affairs the place you have got a tree fall down.
What occurs is that there’s a new useful resource accessible in that habitat on the bottom stage, and that’s gentle. Both poison ivy seeds will germinate, or the rhizomes sprout—these underground, horizontal stems which can be in lots of circumstances underfoot the place you don’t even know they’re. They might sprout stems and are available up above floor, and also you’ll see them.
There could have been poison ivy there in a really gentle approach, possibly a couple of vegetation right here and there, after which as soon as that gentle useful resource is launched by the taking down or falling of a tree, these vegetation are in a position to thicken and develop extra stems and actually take over.
It’s an early successional plant, and develop wells in disturbed areas. Some folks would name it weedy.
Q. You talked about that it could possibly transfer round by rhizomes. It has fruits, so it can be moved round by birds and possibly mammals?
A. The fruits are literally an necessary meals for wildlife; lots of birds eat them. Deer have been identified to eat them, and in some circumstances rodents like mice do. So that they get moved round by way of animals’ guts and deposited in areas away from the plant.
Q. The kind of nursery-rhyme knowledge I used to be taught many years in the past was, “leaves of three run and flee,” however poison ivy isn’t so simply typecast, is it? It may be fairly variable in look, can’t it?
A. It completely can. The leaves will be shiny or not shiny; they will have these crimson stems or petioles or not (they are often inexperienced typically). The shade of inexperienced may be very completely different within the leaves. The leaves will be fairly giant—one leaflet will be the dimensions of your head, or the dimensions of one among your fingers, huge or fairly small.
In some areas sometimes they may have 5 leaflets, not three—although it’s very uncommon. In a single inhabitants in Texas, this attribute has apparently develop into mounted so the whole inhabitants of poison ivy on this one space truly has 5 leaflets. I’ve seen occasional collections from different states which have 5 leaflets. However for probably the most half: Leaves of three, let it’s, or leaves of three, run and flee—these are fairly good rhymes to recollect.
Q. They are saying every thing grows greater in Texas. [Laughter.] The leaf edges will be fairly completely different; you need to look rigorously.
A. It’s so true: The margins of the leaves could also be clean, what we name complete, or they could be toothed, or very jagged, or they could be like an oak leaf.
Q. And the behavior of the plant—the brand new vegetation in my disturbed areas are like a herbaceous groundcover, however alongside my street there are lots of large, hairy-looking woody vines wrapping round trunks of very previous bushes.
A. That’s proper. It may possibly have fairly a distinct behavior, relying on the place it’s rising, and what situations it’s below. Additionally relying on in all probability among the genetic make-up of the plant as properly. A few of these issues traditionally have been handled as separate species or varieties, or sub-species of poison ivy: Generally there’s one attribute was used to acknowledge that—possibly that it’s freestanding, as an alternative of climbing.
However actually after we look throughout poison ivy we see that it may be a climbing plant, as you mentioned. Generally these climbing vegetation can have fairly giant trunks of their very own and large branches, such that in the event that they’re rising up a tree, the branches of the tree may very well be poison ivy branches, not the branches of the tree. Generally the tree it’s on is lifeless and it appears prefer it’s the tree.
Q. [Laughter.] “Little Store of Horrors.”
A. And typically they are often small groundcover, and freestanding. I’ve seen in coastal New Jersey, as an illustration, a shrub of poison ivy that was about 7 ft tall, and had clean black bark. It was positively poison ivy—nevertheless it was this 7-foot shrub with clean black bark.
Q. It’s an necessary plant ecologically—and even a gorgeous plant, as an illustration in fall shade. However no one likes it (aside from you!) as a result of it causes an allergic response in some folks. I’ve to admit: I’ve been crawling round within the underbrush a lot of my grownup life, and I’ve by no means had the rash.
A. About 10 to fifteen % of the human inhabitants is proof against poison ivy, and can by no means have a rash.
I’ve given lectures across the nation about this subject, and somebody will come as much as me and say, “I’m in my 60s, and I by no means had poison ivy, and now I get the rash.” And I say: “Has something modified?” And so they reply that they retired and now they backyard on a regular basis—they elevated their entry, their publicity.
So that you don’t need to get too far forward of your self and assume that you’ve lifetime immunity. I’d say you’re in all probability secure in that assumption since you do have a lot publicity to it, being an avid gardener. However for individuals who haven’t had that type of lifetime publicity and don’t get a rash, I wouldn’t rely myself amongst that 10 to fifteen % who’re immune. You’ll be able to develop a rash later in life, and the extra publicity you have got, the extra possible you might be to get the rash—not the reverse.
Generally folks say, “If I simply maintain exposing myself I gained’t get the rash anymore,” and we don’t actually see that to be true.
Q. Why did the plant develop this chemical—definitely to not torture us, proper?
A. It’s known as urushiol, and mainly these compounds basically solely give folks a rash, although there are some reviews that possibly different primates get it.
These compounds have lots of protecting qualities for the plant—not chasing folks off from choosing the leaves, however truly combating off ailments, microbial assaults: fungal, bacterial and viral assaults. There have been fairly a couple of research which have regarded on the effectiveness of the anti-microbial properties of those compounds.
Q. So it developed urushiols as a protection mechanism in opposition to illness—not in opposition to predation.
A. The compounds don’t appear to have any impact on the animals that eat them. You’ll be able to see poison ivy leaves which have been virtually decimated by varied bugs consuming them. I’ve seen deer grazing on poison ivy, and definitely birds and different different animals eat the fruit.
Q. Does urushiol have any financial makes use of, or makes use of in drugs? I believe I learn it was utilized in Japanese lacquer.
A. In a number of international locations in Southern Japanese Asia, the sap or the urushiols of the bushes of Toxicodendron are harvested—the identical genus we’ve right here, however a distinct species—and likewise bushes from one other genus known as Gluta that happens in that space. They’ll slash the bark—put strains down the bark, and put somewhat bucket there, the identical approach you’d harvest rubber from a rubber tree, and how one can harvest maple sap from a maple bushes, although barely completely different.
They’ll harvest that sap, boil it down for a really very long time, and both use it to use to fantastic woodworking (which is what they do extra in Japan) or to those very weak bamboo constructions, which is what you see in Burma, or Myanmar. They construct these little bamboo constructions, and placed on 10 or 15 or 20 coats of this lacquer—this boiled-down sap from Toxicodendron. They make these lovely artistic endeavors.
Q. I hear folks say they’re going to wait to deal with an invasion until the poison ivy leaves fall in autumn—to keep away from getting the rash. I say, “I don’t suppose so.” [Laughter.]
A. That’s a really unhealthy concept. Each single a part of the plant, besides possibly the precise seed contained in the fruit, could cause a rash. All of them have these resin canals which have the ururshiols in them. In the event you take a look at the fruit within the fall, it’s a gorgeous cream shade—and I say lovely as a result of I like poison ivy, however some folks don’t.
Q. Since you’re a nutty, botany type of individual. [Laughter.]
A. The fruits have black strains in them, and people are literally these resin canals. They’re current all through the plant. In the event you snap off a leaf or minimize the stem and see the sap popping out of it, you may watch it turning black because it oxidizes with publicity to the air. That black sap is what’s going to provide the rash. That black sap runs within the stems within the wintertime; it’s nonetheless current within the leaves that fall off. I’ve heard of individuals getting rashes from 20-year-old vegetation which have been collected and dried and pressed in our natural-history assortment.
I’ve heard of individuals getting rashes from gardening gear they hadn’t utilized in two years, as a result of it wasn’t washed correctly.
Q. Folks make the connection that as a result of jewelweed typically grows close to poison ivy, they suppose in the event that they put the jewelweed on that can resolve every thing, however that’s not proper, is it?
A. No, it’s not. Jewelweed has some properties that convey swelling down, so it will be fantastic to make use of jewelweed after you have got the rash and have some swollen areas. Nevertheless it’s not going to do something to forestall the rash.
Principally these compounds, the urushiols, bind to your pores and skin cells—to the little proteins in your pores and skin cells. So in the event you’re somebody who’s going to get a rash, you’ll get it. The important thing factor is to forestall the binding from taking place—to scrub, and take away all these oils as quickly as you probably can after coming into contact with it.
There are some nice merchandise on the market, like Tecnu, which mainly binds to the urushiol earlier than it could possibly bind to your pores and skin cells.
Q. You’ll be able to’t unfold the rash unfold to your self or others, when the blisters break, or in the event you contact the rash to a different a part of your physique or to another person?
A. When you wash your self, or wash your instruments or your canine—in case your canine’s been romping within the poison ivy—there’s nothing on you or in that rash, even when it’s oozing, that may trigger a rash. What you see in your physique is definitely your individual immune system combating your individual physique. The binding of the urushiols to the proteins in your pores and skin cells makes your immune system acknowledge your physique as overseas, and assault them. All of these liquids that come into that rash don’t have anything to do with the poison ivy plant—it’s your individual physique fluid.
Q. So what do I do subsequent with my backyard invasions of poison ivy? Normally I dig it out and bag it up or get rid of the dug-up vegetation within the woods.
A. If in case you have the wherewithal to dig it out, that’s a extremely good methodology. I’m a proponent of not utilizing lots of chemical substances within the backyard, however you probably have a extreme allergy to it and should eliminate it, I might say very selective functions of herbicides—portray it onto the leaves straight, and never doing wholesale spraying—is an applicable utility, in my view.
You are able to do bodily elimination, however these rhizomes are actually robust, and whenever you break them up even a tiny fragment can resprout. So it’s very exhausting to take away all of it, if that’s what you need to do.
Q. So mainly I ought to simply quit, is that what you’re telling me? [Laughter.]
A. And benefit from the lovely fall shade, and know that you just’re feeding birds.
Q. I do find it irresistible alongside the outer property edge and all the time go away it there. I’m simply not so completely satisfied that it’s now romping in among the many perennials.
So in our shifting local weather, I think about this is likely one of the creatures that’s doing properly.
A. It’s. There was a research accomplished in 2006 out of Duke Forests by Duke College. They’ve a forest the place they’re growing the carbon dioxide ranges artificially—actually mimicking what we estimate would be the state of affairs with local weather change. What they discovered is that just about all vegetation develop higher once they have extra carbon dioxide, similar to we do when we’ve extra oxygen. However additionally they discovered that the urushiols are worse—so what we’ve to stay up for is extra poison ivy, and meaner poison ivy.
Q. Effectively aren’t you simply Miss Perky over there? [Laughter.] Thanks a lot for all the knowledge on poison ivy.
visiting the u.s. botanic backyard
THE UNITED STATES Botanic Backyard the place Dr. Susan Pell is Govt Director is located on the foot of the Capitol Constructing, on the Mall, in Washington, D.C. There’s a historic conservatory, plus out of doors gardens, with reveals and public applications, and an in depth plant assortment with a variety of habitats represented open air and in.
The Backyard provides a medicinal and toxic vegetation tour fairly commonly (see the occasions calendar).
desire the podcast model of the present?
MY WEEKLY public-radio present, rated a “top-5 backyard podcast” by “The Guardian” newspaper within the UK, started its sixteenth yr in March 2025. In 2016, the present gained three silver medals for excellence from the Backyard Writers Affiliation. It’s produced at Robin Hood Radio, the smallest NPR station within the nation. Hear regionally within the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Japanese, rerun at 8:30 Saturdays. Or play the Sept. 1, 2025 present utilizing the participant close to the highest of this transcript. You’ll be able to subscribe to all future editions on Apple Podcasts or Spotify (and browse my archive of podcasts right here).
(Poison sumac picture from Wikimedia Commons. Disclosure: Purchases from Amazon affiliate hyperlinks yield a small fee.)
