Gardening Columns

Don't let this delicate little shoot fool you --
it's poison ivy and it's loaded with urushiol, the oil
that causes the itchy rash.

Leaves of Three

First published on garden.org on March 29, 2007, by Suzanne DeJohn

Springtime in the South -- when gardeners' thoughts turn to tulips and trilliums, bluebirds and bluebells. And for some of us, poison ivy. If you've ever had to endure the maddeningly itchy rash, you're not alone. Four out of five people develop skin lesions upon exposure to poison ivy, or more specifically to urushiol (oo-roo-shee-all), the oil contained in the sap. Approximately 350,000 cases of poison ivy-related dermatitis are reported each year. (I don't know about you but I get poison ivy every summer and I've never reported it to anyone except my long-suffering husband, so I'm betting that the number of actual cases is much, much higher.) On the misery index, poison ivy rivals toothaches and long lines at the DMV.

Identifying Poison Ivy
"Leaves of three, let it be" is the easiest way to remember how to identify this plant, but it's not foolproof. Poison ivy (Toxicodendron radicans) leaves usually have three leaflets. However, occasionally they have five and sometimes up to nine leaflets. The leaves are relatively shiny and smooth (as opposed to wrinkled raspberry leaves), and the margins are usually smooth or slightly lobed (as opposed to deeply lobed oak leaves or serrated rose leaves). The plants may take the form of a woody vine, a trailing ground cover, or a free-standing shrub so you'll need to look up, down, and all around.

First Aid
If you know you've been exposed, there's no time to waste in treating the area -- urushiol can penetrate the skin in minutes. Unfortunately, resources offer conflicting information on treatment. The U.S. Food and Drug Administration Web site suggests removing contaminated clothing and cleansing the skin with isopropyl (rubbing) alcohol. Then wash skin with water only. Avoid soap at this point because the soap can pick up the oil and spread it around. After washing with alcohol and plain water, you can go ahead and shower with soap. Wipe down tools with rubbing alcohol and launder clothing.

The National Park Service Public Health Program, on the other hand, suggests avoiding alcohol because it will spread the urushiol, and instead suggests washing with soap and cold water (cold water because hot water will open the skin's pores, allowing the urushiol to enter).

With some hundreds of thousands of cases of poison ivy reported each year, and likely millions of unreported ones, you'd think researchers would have a definitive answer on something as simple as the alcohol vs. soap question. But I suppose we'll each have to figure out what works best. Keep a stash of rubbing alcohol, soap, or purchased poison ivy treatment and some disposable gloves with your gardening supplies for poison ivy triage. If you can do the initial washing outdoors, you'll avoid bringing the oil into the house. Of course, the practicality of this will depend on how much clothing you need to remove and/or the proximity of your neighbors.

Prevention
There are products touted as poison ivy preventatives. I can't vouch for them because I haven't tried them. Most entail rubbing a lotion on your skin, either to act as a barrier to urushiol or to indicate when you've been exposed so you can wash immediately. Because I weed for a few minutes here and there several times a day, I don't think these would be a practical choice for me. But if you weed for hours at a time, they might bear looking into.

Eradication
When talking about weeds I usually use the term "manage" as opposed to "eradicate." Weeds are nature's way of quickly covering barren ground, protecting soil from wind erosion and compaction by heavy rains. Poison ivy is different. I want to eradicate it from my yard. If any plant could be called sneaky and spiteful, it would be poison ivy. It's everywhere in our yard -- even crouching down in the lawn, ready to pounce on unprotected toes.

If you need to get rid of poison ivy in a small area, you can try smothering it by covering the area with newspapers or cardboard and a thick layer of mulch. You'll have to keep an eye on it to make sure the vines don't find a way out. If you're not allergic you can try pulling young vines with gloved hands, but know that repeated exposure can lead to an allergic response even if you've never had one before. Poison ivy holds the honor as the only plant I'll treat with glyphosate herbicide. I can't smother it because the vines are everywhere, and I'd likely end up in the hospital if I tried. I certainly can't pull it out. Used judiciously, glyphosate herbicide is probably the safest treatment.

If it seems like there's more poison ivy around than ever before, you may be right. Poison ivy prefers "edge habitats" -- disturbed areas near woodlands. With development reaching further and further into previously wooded areas, poison ivy is finding a perfect niche where civilization meets wilderness. Other woody weeds, such as Japanese honeysuckle, are also thriving.

The proliferation of poison ivy may be yet another negative impact of global warming. Duke University researchers conducted a six-year study using growth chambers to assess the impact of elevated atmospheric carbon dioxide (a leading cause of global warming) on poison ivy growth. They discovered that higher carbon dioxide levels increased photosynthesis, water use efficiency, and growth of poison ivy -- more so than for other woody plants. And the plants produce an even more toxic form of urushiol under these conditions, too. When it comes to the impact on my everyday life, the other ramifications of global warming -- melting polar ice caps, rising sea levels -- are relatively remote. The threat of more vigorous and more toxic poison ivy really hits home.