Poison Ivy

Each poison ivy leaf is made up of a set of three leaflets. It’s the leaflets, not the leaves that the old saying “Leaves of three, let it be.” is referring to. Photo credit: Broly0, cc-0

Poison ivy (Toxicodendron radicans) is a common and much-hated native plant that can be found throughout the eastern half of the continent. It seems to grow pretty much anywhere and the allergic reactions it can cause are infamous. However, no matter how much we may hate it, poison ivy plays an important role in the ecosystem.

Poison ivy has two different growth forms. The first is as an herbaceous plant growing along the ground, typically only 6-18 inches tall and often forming a dense ground cover. The second is as a woody vine, often climbing high into the tree tops. One way to identify poison ivy vines from other woody vines growing up a tree is that poison ivy vines have lots of thin rootlets that grow out of the vine and attach it to the tree, much like fingernails clawing into the bark. All of those rootlets going up and down the vine can make it look hairy. Most of our other native, woody vines either aren’t hairy or aren’t nearly as hairy.

The leaves are perhaps the best known way of identifying poison ivy. Poison ivy leaves are made up of three leaflets. The old saying “Leaves of three, let it be,” is more accurately stated as “Leaflets three, let it be.” Poison ivy leaves are typically a dark green and can have a slightly shiny look to the top of the leaves. In the fall, they turn bright red. In fact, poison ivy was actually introduced to parts of Europe partly for erosion control and partly for its fall foliage.

Poison ivy can grow as an herb or as a vine. It is easy to identify the woody vines, even if you can’t see the leaves because poison ivy vines often look hairy. Large, mature vines will look hairier than smaller, younger vines. If you spend much time in the woods, being able to identify poison ivy without the leaves can be important because the stems and roots also contain urushiol. Photo credit: Nicholas A. Tonelli, cc-by 2.0

Poison ivy blooms in late spring and early summer. It has small, greenish flowers that are produced in loose clusters. Many different species of bees, including honey bees, will work poison ivy flowers. Ants and wasps are also important pollinators of poison ivy, although beetles, flies, and butterflies will also visit the flowers. We tend not to notice how important poison ivy can be to pollinators because no one wants to go digging through poison ivy leaves to find the small, inconspicuous flowers and see what is working them.

After the flowers are pollinated, they form small, white fruits that kind of look like grapes. Again, they are often hidden among the leaves where no one wants to go looking to see what is eating the fruits. At least 75 different species of birds have been recorded eating poison ivy fruit. Squirrels, deer, and many other mammals will also eat the fruit and leaves. Like I said, it plays an important role in the ecosystem. So if everything else can eat poison ivy, why do we have so much trouble with it?

Poison ivy sap contains an oil called urushiol. Urushiol is found in the stems, leaves, and roots of the plant and essentially acts as a liquid Band-Aid to seal any wounds the plant may get. It does nothing to keep critters from eating the plant. Our bodies basically have an over-reaction to absolutely nothing.

If you come in contact with poison ivy, wash the exposed skin as soon as possible. Urushiol can bind with your skin within 10-30 minutes. The oil can also stay active on clothes, pet fur, gardening tools, etc. for quite a while so be sure to wash anything that may have contacted the plant. Even if you are one of the lucky ones who isn’t susceptible to poison ivy, wash up so you don’t accidentally get the oils on someone else. The rough estimate that I keep seeing is that around 80% of the population is allergic to urushiol. Oh yeah, and just because you aren’t allergic to it now doesn’t mean that you won’t eventually develop an allergic response to it.

It usually takes 12-48 hours after the oil has bonded with your skin for the rash to appear. The intensity of the rash can vary based on how much urushiol you came in contact with and on how allergic you are to the oil. The good news (if you can call it that) is that once the oil has bonded to your skin, you can’t spread it to anyone else. The liquid that can seep out of the blisters, can’t spread the rash either.

Poison ivy flowers are highly attractive to many different bee species. We just tend not to notice because most of us don’t want to get close enough to look for the tiny flowers, much less see who might be pollinating it. Photo credit: Bob Peterson, cc-by 2.0 

If you find poison ivy trying to invade your yard or gardens, putting on several pairs of plastic gloves and pulling it might work if it is just getting started. However, if it is growing along the ground, then it will have a long rhizome and can sprout back if you break the rhizome. If it is a vine or a more established patch, then spot treating it with an herbicide is likely your best bet. However, even after it is dead, still wear gloves when you pull out the dead stuff. Whatever you do, DO NOT burn poison ivy. The urushiol can be carried by the smoke and if you breathe the smoke, then it could cause a serious allergic reaction in your lungs and throat.

Although poison ivy is a good plant for pollinators and wildlife, this is one native plant that I don’t recommend planting. Appreciate its value and let it grow in the woods, fields, and more natural areas, but don’t include it as part of your pollinator garden.

This article was part of Shannon’s original Kentucky Pollinators and Backyard Wildlife blog which evolved into the blog for Backyard Ecology.

Backyard Ecology: Exploring Nature in Your Backyard
Nature isn’t just “out there.” It’s all around us, including right outside our doors. Hi, my name is Shannon Trimboli, and I am the host of Backyard Ecology. I live in southcentral Kentucky and am a wildlife biologist, educator, author, beekeeper, and owner of a nursery specializing in plants for pollinators and wildlife conservation. I invite you to join me as we ignite our curiosity and natural wonder, explore our yards and communities, and improve our local pollinator and wildlife habitat. Learn more or subscribe to my email list at www.backyardecology.net.

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