Poison Oak Plant Profile

Toxicity and Special Considerations

Poison oak leaves

 Darren415 / Getty Images

Poison oak is not an oak but a low-growing deciduous shrub. Its stems and leaves contain urushiol, a natural oil that causes a severe skin rash any time of the year, even in the winter when the shrub has no leaves.

The plant is native to north America and as such has significant wildlife value: Birds like robins like the berries, songbirds feed on its berries during fall migration, and other birds feed on the insects that live on poison oak.

However, when poison oak pops ups in your yard, protecting yourself from its dangers should take precedence over any wildlife considerations. After proper identification, it should be removed safely.

Familiarizing yourself with poison oak will also help you identify poison oak it in the wild so you can avoid exposure.

Toxicity of Poison Oak

Urushiol, the natural oil in the leaves and stems of poison oak, causes allergic reactions in humans year-round. Upon contact—and mere brushing against it can be enough—it sticks to the skin, and it is absorbed by the surrounding skin cells. Within one to six days, this leads to skin irritation and itching, followed by water blisters. The allergic reaction usually subsides within ten days, but if a sensitive person is repeatedly exposed to poison oak, the reaction gets more severe every time.

Furry pets are usually not affected by poison oak, with the exception of a dog nose or the underbelly where the coat is thin.

What makes poison oak particularly vicious is the potential of indirect transmission, as the oil also sticks to surfaces such as clothing, gloves, tools, and to the fur of pets, from where it can spread.

After exposure, thoroughly wash skin, tools, shoes, and other surfaces with warm soapy water and rinse with plenty of cold water. Contaminated clothing should be washed separately in a hot washing cycle.

If you suspect your dog was exposed to poison oak, give your pooch a bath with pet soap and wear disposable gloves.

Poison oak has a cluster of small berries
Poison oak has a cluster of small berries. step2626 / Getty Images

Gardening Considerations

If poison oak pops up in your yard, it was most likely brought there by birds who eat the berries. The plant that is visible to the eye grows slowly, but poison oak develops a large underground root system. Because it’s so dangerous to humans, it is crucial to identify and remove it as soon as it pops up.

Botanical Name Toxicodendron diversilobum
Common Name Poison oak, western poison oak, Pacific poison oak
Plant Type Perennial
Mature Size Three to six feet height
Bloom Time Spring
Flower Color White-greenish

Identification of Poison Oak

Poison oak belongs to the same genus as poison ivy and poison sumac, and it has similar botanical characteristics.

Like poison ivy, a single leaf consists of three leaflets, or three-parted leaves.

The stem of the center leaflet is longer than the stem of the leaflets on either side. Not all leaves are equally lobed, but when they are, they resemble oak leaves, which gives the plant its common name. The size of the leaves varies even on the same plant; the average leaf length is about six inches.

The new leaves in the spring are reddish, and because of the oil they contain, appear shiny. Later the leaves turn green. In the fall, before they drop, they turn into different shades of red and yellow.

Also, both the stems and the leaflets of poison oak are covered with fine hairs.

The clusters of small, white-greenish flowers in late spring turn into small, waxy, greenish-yellow or white berries in late summer. The berries often remain on the plant through early winter.

During dormancy, without the characteristic leaves, poison oak is much more difficult to identify. The stems are light brown, cinnamon-colored, or grayish, with an upright growth pattern, like sticks.

The absence of leaves makes it difficult to identify poison oak in the winter
Poison oak in the winter. Darren415 / Getty Images

Where Poison Oak Is Found

Pacific poison oak is mostly found in the western United States, from Washington to California. It grows in woodland, grassland, hillsides, and coniferous forests but also along roadsides, in abandoned farm fields, and wasteland.

In full sun, poison oak is a dense shrub whereas in shady locations, it grows as a vine, reaching for the light and clinging onto trees or other vertical support.

Warning

Never burn poison oak. The toxic oils are released into the air through the smoke particles and can cause severe respiratory irritation.

How to Remove Poison Oak

There are two different ways to remove poison oak: manually, or with herbicides. The advantage of manual removal is that you can do it any time during the year, whereas herbicide applications need to be timed according to the growing stage of the plant. More details can be found in this article How to Get Rid of Poison Oak.

Varieties of Poison Oak

Atlantic poison oak (Toxicodendron pubescens) is native to the southeastern United States. It’s the eastern counterpart of the Pacific poison oak. Everything stated above about the toxicity also applies to the Atlantic poison oak.