Poison ivy (Toxicodendron radicans) is a noxious weed commonly found growing in home landscapes, along roadsides, in forests, and even in urban areas in North America. Its toxicity is based on an active irritant called urushiol, an oily resin contained in all parts of the plant. Pets are less likely to be troubled by poison ivy but are occasionally affected by it as well.
The scientific name of the plant is Toxicodendron radicans. Knowing the old rhyme of "Leaves of three, let it be" is a nice start, but it does not go far enough. These photos will allow you to identify the plant both with and without leaves and at various stages of maturity.
8 Facts About Poison Ivy
While the leaves are the most toxic part of the plant, contact with any part (even when the plant is bare of foliage) can cause an allergic reaction. Even if your cat or dog comes in contact with the plant, the animal can spread it to you. That is the reason why it is important to learn what poison ivy looks like throughout the growing season and beyond. This leaf close-up shows plants that are less than a foot high but that have already put on their green summer color.
Where Poison Ivy Grows
Poison ivy is native to the eastern United States and eastern Canada; therefore, by definition, it can't be considered invasive there, even though it spreads aggressively even in that region. But it could be invasive in regions to which it has been introduced. Poison ivy is not fussy about sun and soil conditions, which is one reason why it is such a successful weed.
01 of 09
Leaves of Young Plants
Young poison ivy plants often start out in spring with orangey or reddish leaves. Be aware that the margins of the leaves sometimes have notches in them (but not always, so this feature, in and of itself, is not enough to identify the weed). The plants here are just barely off the ground but the oil (urushiol, which is what makes this plant toxic) can still rub off on the fabric of shoes and socks. It is possible to transfer the oil from your clothes to your skin so, be careful removing the garment if you think it came into contact with poison ivy.
02 of 09
As summer progresses and poison ivy plants mature, most of the leaves are green, and they are about two feet high. Any new leaves that appear, though, will still be reddish, as in spring (but the red color will not be as intense). Poison ivy vines often grow in a mass, taking over an area and becoming the dominant plant.
03 of 09
People seldom associate something as nasty as poison ivy with flowers, but, yes, this weed does bloom. Perhaps ironically, the blossoms are not especially attractive. The flower buds, which form in clusters, look like tiny specks of green if you are just glancing quickly at the plant.
04 of 09
Poison ivy produces rather small, unremarkable blossoms that are off-white in color with orangey centers. Unopened buds that are close to opening are also off-white. You will sometimes see a plant with both opened and unopened flower buds at the same time (as in this example). Walking quickly past a patch of poison ivy plants in bloom, you would hardly notice the individual blossoms.Continue to 5 of 9 below.
05 of 09
Poison ivy plants also grow berries, which are just as toxic as the rest of the plant. An identifying trait of poison ivy is the color of its mature berries. When they ripen (in late summer to early fall), they turn from a pale green to a whitish color. Poison sumac also has a curious white berry.
06 of 09
Fall Foliage: Orange
The green summer color of poison ivy's foliage yields to brilliant fall foliage in red, yellow, or orange. The autumn brilliance of poison ivy's foliage is due to the anthocyanin pigments characteristic of the plant family to which poison ivy belongs. Poison oak and poison sumac turn similarly colorful shades in fall. All three plants are members of the cashew family (Anacardiaceae). The color in autumn is as breathtaking as it is on any of the trees grown for their colorful fall foliage.
07 of 09
Fall Foliage: Red
Poison ivy plants tend to come "full circle." If they came out of the ground in spring with red leaves, they often will display reddish fall foliage. In this regard, poison ivy reminds you of red maple trees. The latter display red buds in spring that hold a hint of what their gorgeous fall foliage will look like.
08 of 09
Have you wondered what those hairy vines are that you sometimes see climbing up trees or bristling along the tops of logs resting on the forest floor? That is what poison ivy looks like in winter after the old leaves have fallen off and before spring's new leaves can take their place. The "hairs" are the vines' aerial rootlets. These rootlets can cling to surfaces, allowing the vines to climb. This is why trees, tree stumps, and stone walls are often seen covered in the vines. When poison ivy has been climbing a tree for a long time, the vine can become so embedded into the tree's bark that it largely disappears from sight, with only the rootlets visible.Continue to 9 of 9 below.
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The Vines Can Damage Clapboard
Unfortunately, winter's "hairy" vines are as toxic as the rest of the plant during other seasons of the year. Poison ivy vines can also climb up the walls of buildings. If they are allowed to climb up the side of a house, garage, barn, or outdoor storage shed sided with clapboards, they can wreak havoc with the clapboards over time, necessitating repair work.
How to Remove Poison Ivy
Poison ivy should be removed from your property so that you don't accidentally make contact with it while gardening. It is possible to safely eradicate poison ivy, whether organically (manually) or with herbicides, but you must take extreme precautions and it might take several attempts. When working around poison ivy, it's especially important to wear gloves (wash the gloves and your clothes separately afterward from your other laundry) so that any residue you came in contact with isn’t transmitted to your food, your face, your pets, other people, or any other surfaces.