A John Deere Publication

Closeup of a poison ivy plant showing three green leaves

Poison ivy leaves grow in distinct three-leaflet clusters. Unfortunately they also can be hard to distinguish from blackberry, raspberry, and box elder leaves. If you look closely, the third leaflet has a longer stem.

Rural Living, Education March 01, 2025

Leaves of Three

Poison ivy is easier to avoid than it is to eliminate.

by Lorne McClinton

Who would think that such harmless looking little plants can be so nasty? But there's a reason it's called poison ivy (Toxicodendron radicans). Nearly all parts of the plant, native to Eastern Canada and the United States, contain an oily resin called urushiol. It's so toxic that even the most incidental contact with it will cause poison ivy rash, redness, itching, swelling, painful skin blisters, and even difficulty breathing in up to 85% of the American and Canadian population.

"I've been dealing with poison ivy all my life," says Gary Bell, a retired biologist and naturalist from Wolfe Island, Ont. "It's one of those plants I have conflicting feelings about. It has this toxic oil throughout the plant. You likely won't develop a rash if you just brush against the leaves if there is no oil on their surface. But if you crush a leaf, a branch, pick a berry, or dig up a root, most will."

It can be hard to avoid if you spend much time in the woods. Bell has had poison ivy rash many times. Usually, it's been a minor inconvenience, but he's known people who were exposed to it by breathing in smoke and were hospitalized because of it.

"It was just awful," Bell says. "The worst case of poison ivy I personally had happen while I was working with a fire crew creating a fire line through brush for a prescribed fire to improve habitat on this nature reserve. I must have moved or cut a branch of poison ivy or poison oak with my leg. A few days later I got a huge blister on it. I had to take prednisone and put cortisone ointment on it. When I finally got rid of it and went out in the field again, I developed it again in the same spot. I took my jeans off when I got home that night and found an oily spot on the inside thigh where the sap had soaked into the denim. I'd just re-exposed myself."

You don't even need to leave your house to be exposed to poison ivy, Bell says. He personally was given a poison ivy rash a couple dozen times by his dog. Dogs—and most animals—aren't affected by it. So, if they happen to run through a patch, they can bring the oily resin in with them on their fur. Then when you give them a hug, you'll have poison ivy all over your arms, chin, and neck.

Poison ivy is usually only a minor inconvenience, Bell says. But it's important to lots of wildlife species. Many feed on its berries. It's also a forest cover plant; it provides understory, shade, and protects the soil with its root system.

It's difficult to eradicate poison ivy if it's on your property, Bell says. Cutting it, burning it or digging out the roots isn't effective. One possibility is covering it in plastic mulch and leaving it for a couple of years. Herbicides are an option too, but the leaves have a waxy layer, so you need to use a herbicide with a surfactant and likely apply it multiple times to get rid of it. It's very hardy.

Above. Squirrels, mice, and chipmunks love poison ivy’s distinct white berries. Gary Bell says they will spread the seeds across the area. Poison ivy is often found along the forest edge or in its understory.

Rodents love them. "A big plant will produce thousands of seeds in these lovely little white berries every year," Bell says. "Squirrels, mice, and chipmunks really love them. Chipmunks fill their cheeks with the little berries and then go bury them and plant them in other places. So, if you have poison ivy and chipmunks you're going to have more poison ivy."

Likely the best option for poison ivy is learning to identify it— and then avoid it. Unfortunately, it's not the easiest plant to identify. There's a reason that there are so many cautionary folk rhymes to help. These include: Leaves of three, leave them be; Longer middle stem, don't touch them; and Hairy vine, no friend of mine.

Keep an eye out for the plant's distinctive three leaf bunches. It sounds simple, but they look a lot like blackberry, raspberry, and box elder leaves. The second rhyme, Longer middle stem, don't touch them, requires a closer look at the leaves. The third leaf will have a distinctive long stem reaching out from the two side leaflets. The last, Hairy vine, no friend of mine, is evident in fall after the leaves have dropped. At this time of year, you can identify poison ivy by the tiny hairy tendrils it uses to climb rocks and tree trunks.

If you've been exposed, the Mayo Clinic's website advises washing affected areas (and clothing) right away. It can take anywhere from 12 to 48 hours for the rash to develop. Lotions or cool baths can help, but if symptoms are severe, or if you are having difficulty breathing, seek medical attention. ‡