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In our enthusiastic haste to get out into the garden as spring approaches, we sometimes forget the hidden hazards lurking about our property. Many native plants are poisonous in one way or another; other species have been introduced into temperate zones and have flourished. Knowing what you're dealing with is paramount.
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 We'll start with the most common three dangerous plants found in the landscape, but not necessarily in order of toxicity: Poison Ivy, Poison Oak, and Poison Sumac. These plants are contact-poisonous, meaning they will cause an external reaction if touched. These plants are so widespread that they account for an estimated 10% loss of work time for the U.S. Forest Service.1 Firefighters battling the California fires are often disabled by the airborne toxins.
Poison Ivy (Toxicodendron radicans). "Leaves of three, let it be" is good advice! But it's interesting to learn that many people don't recognize this fast-growing intruder. Many homeowners mistake it for a close look-alike: Virginia Creeper (Parthenocissus quinquefolia), of which only the berries are toxic, and only if eaten.
Both plants are climbers, and both plants have brilliant red foliage in the fall. However, though the tiny, newly emerging leaves of Virginia Creeper are indeed three-lobed, if you follow the stem back toward older growth, you'll see five distinct leaves with toothed edges. In contrast, Poison Ivy has shiny leaves with smooth edges.
All parts of Poison Ivy are toxic (leaves, stems, roots, blooms, berries); the culprit is urushiol, a substance that seems to have an unlimited shelf-life. Individuals who are highly allergic to Poison Ivy can react to even the handling of dead leaves and stems, or petting a dog or cat that has brushed against the plant. Even people who are not normally sensitive can have severe reactions by breathing the smoke of burning Poison Ivy. Eradicating this weed from your landscape should be done thoroughly and with care. NEVER burn Poison Ivy. When working around it, cover up, wear gloves, and dispose of the plants in plastic bags. Some commercial products can be applied before contact to prevent or at least lessen exposure.
Poison Oak (Toxicodendron diversilobum) is the western counterpoint of Poison Ivy. Poison Oak grows solely in the western United States, from southern British Columbia to northern Mexico; references also cite subspecies identified in Malaysia, China, and Japan. Poison oak can be difficult to identify because it displays in several forms: low ground cover, vining, or very mature specimens in shrub form. Leaves with three lobes are oak-shaped and shiny; the leaves turn brilliant red in fall. Poison Oak forms small white berries that remain on the stem after the leaves drop.
All parts of the plant are toxic and should be avoided. When taking Poison Oak from your property, exercise care, always cover up and wear gloves. NEVER burn either living plants or those that have been pulled or cut. Dispose of the materials in heavy plastic bags.
Special care should be taken in early spring when these plants emerge as new growth. They often blend in with the surrounding foliage and it only takes one brief contact for them to do their damage.
Poison Sumac (Toxicodendron vernix) is listed as one of the "U.S. Invasive Weeds"2 and is considered more virulent and dangerous than either Poison Oak or Poison Ivy. Poison Sumac can be small and shrubby, or grow up to 20 feet tall. The frond-like pinnate leaves are attractive, especially in fall when they turn scarlet. In June and July, the plant blooms, forming long panicles of yellow-green flowers. Poison Sumac grows as far west as Idaho (though only in the southern part); the plant prefers swamps and bogs, or other very wet soil.
The same precautions should be taken when working around Poison Sumac as with all other contact-poisonous plants. Use good sense and, when necessary, call in a professional to deal with large areas of poisonous materials.
1 http://waynesword.palomar.edu/ww0802.htm
2 http://plants.nrcs.usda.gov/cgi_bin/invasive/all.cgi
 | Toni Leland has been writing for over 20 years. She has written a biweekly gardening newspaper column as a spokesman for the Ohio State University Master Gardener program, and writes for Grit magazine and Romance Writers Report. She has been a gardener all her life, working soil all over the world. In her day job, she scripts and produces educational DVDs about caring for Miniature Horses, as well as writing and editing books about this unique height breed. |
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Subject: Virginia Creeper hazard
Posted by MOWIVA (from Virginia Beach, VA) on April 18, 2008 at 12:28 PM:Please don't let folks think Virginia creeper is benign. I've gotten terrible rashes from Virginia creeper. To quote David Beaulieu on About.comLandscaping:
While Virginia creeper vines do not contain urushiol oil, the compound that makes Rhus radicans (poison ivy) toxic, reader Paula Brooks has informed me that some people need to shun contact with Virginia creeper, too. It turns out that the sap flowing through Virginia creeper vines contains oxalate crystals, which can be toxic to some people. If you're unsure as to whether you're one of those people, don't touch Virginia creepers, since the result of contact could be a nasty skin rash.
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Subject: poison ivy
Posted by Outcast (from Bladensburg, MD) on April 14, 2008 at 12:27 PM:What is a good spray to put on poison ivy to kill it? I have a mess of it in my yard and I am highly allergic to it. ... Posted by herbspirit (from Southborough, MA) on April 14, 2008 at 1:42 PM: Grow some Jewel weed (Impatiens capensis or pallida) if you don't already have it. They often grow together if it's in a wet area. Break open the stem of the Jewel weed and rub it on the area exposed. The chemical in Jewel weed (lawsone) binds to the same receptors as urushiol, and will help prevent the rash. ... Posted by laura10801 (from Fairfield County, CT) on April 14, 2008 at 9:48 PM: Roundup has a spray that is specifically made for poison ivy. I've used it with success.
If you have touched poison ivy and know it, wash the area with cool water and soap for a good long time as soon as you can. This will remove some of the urushiol and reduce the intensity of the contamination. ...
Subject: allergic
Posted by LouC (from Desoto, TX) on April 14, 2008 at 9:51 AM:After over a half-century of life, I developed and allergy to poison ivy. Sometimes just the name seems to be avoided. Thank you for a very comprehensive article. I shall print it and keep it near so I can compare growth.
So glad we harrased you into joining DG.
Christi ... Posted by shadowpaige64507 (from Birmingham, AL) on April 14, 2008 at 10:37 AM: I'm one of the few people that Poison Ivy has no affect on me. When ever I go home to visit my mom she has me pull it from the ground. I never wear gloves. But my brother is highly affected by it. Strange how things work. ... Posted by Kelli (from Los Angeles (Canoga , CA) on April 14, 2008 at 12:31 PM: Be careful, Shadowpaige. I've heard that too much exposure can cause a person to lose his/her immunity. I don't know if that is true. I seem to be immune but I still avoid it.
I have heard that some American Indians were immune to poison oak and would sometimes use the branches in making baskets. Decades later, researchers handling the baskets would come down with poison oak. Again, I don't know if this is true. ... Posted by Shirley1md (from Ellicott City, MD) on April 14, 2008 at 12:33 PM: I am sooo incredibly allergic to them! I break out in a severe rash at least a couple of times during each gardening season. Last Summer I was clearing out some weeds and did not know what Poison Sumac looked like. Boy, did I find out the hard way!!!
It is also very important to note that these poisonous vines are even more toxic during the winter time when their leaves are not visible. You can identify, at least Poison Ivy, by its fury looking vine clinging to the tree's bark. DON"T TOUCH IT! ... Posted by joegee (from Bucyrus, OH) on April 14, 2008 at 10:08 PM: As a child I was once exposed to poison ivy smoke when a maintenance man at my school burned out a hedge row with gasoline. We had dozens of students out sick. I got pneumonia, and I had to go through a few rounds of steroids (including injections.) I carried scars for several years.
I can definitely add to the "do not burn" caution. Airborne urushiol can kill!
I also went through the poison ivy allergy shot regimen. It didn't work.
Leaves of three, LET IT BE!
-Joe G.
... Posted by Calif_Sue (from San Jose, CA) on April 15, 2008 at 2:31 PM: {Shiver} Had to learn what all stages of poison oak looks like as I had a bad case of it and had to get a prednisone prescription, which gave a me other problems so I quit that. Nasty stuff. Carry Technu in my car now as we like to hike in the surrounding hills. ... Posted by joegee (from Bucyrus, OH) on April 15, 2008 at 2:40 PM: Oddly enough, I have found that I also respond in a similar way to cashews, another member of the same family as our poison ivies, [HYPERLINK@davesgarden.com] . If I eat cashews in sufficient quantities a nasty rash expresses itself on the soles of my feet and the palms of my hands. I no longer buy pound cans of cashews. :P
-Joe ... Posted by LouC (from Desoto, TX) on April 15, 2008 at 3:41 PM: That is interesting, Joe. Possibly others have had similar problems and never put it together. ... Posted by ebony2 (from Spokane, WA) on April 17, 2008 at 3:26 AM: I take exception to the comment that Virginia Creeper isn't poisonous. For me it is. Just a touch results in a widespread itchy rash that lasts more than a week - and I'm not having much luck getting rid of the plant. Guess I'll have to learn to use gloves whether I like them or not. ...
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