Poison Ivy and Poison Oak

Poison ivy, poison oak share many similarities

Brian Jervis: Ask a Master Gardener

Saturday, October 10, 2015

Q: I think I can recognize poison ivy; what does poison oak look like? Do we have it in Oklahoma? How can I identify it? A. G., Tulsa

A: We do have a variety, Atlantic poison oak, in our state, but it is not nearly as common as poison ivy. They share many similarities and both have the capacity to cause severe allergic rashes in about 85 percent of the population.

There is a third plant in the “poison” group called poison sumac. It is rare in Oklahoma and more common to the south and east coastal states.

Some of the keys to identifying poison oak and poison ivy are interchangeable. They both have leaflets of three to a stem. The leaflets and stems are distributed on the plant in an alternating fashion, and they are not opposite each other where they originate. Likewise, the leaf veins are not opposite but alternate where they connect in the center of the leaf.

Of the three leaves, the middle one has a much longer stem than the other two. If leaves have no stems, it is a different plant. The leaf size and shape are variable for poison ivy, but poison oak typically has a shape similar to a white oak, with scalloped edges, and may be 6 or more inches long. Both plants are extremely colorful in the fall.

Poison ivy and poison oak have small off-white flowers, which produce white pea-sized berries. If berries are red, blue or purple, it is not one of these. Each of these plants can grow as a shrub several feet tall. Poison ivy may form a vine but not poison oak. The poison ivy vine may be an inch or more across and almost always has dense hair-like aerial rootlets for attachment to trees. Vines grow straight up a tree. If the vine twines or circles a tree it is not likely poison ivy.

In winter, identification is difficult. If berries are still present, this helps, but an expert is required to identify bare stems. It should be kept in mind that the toxin in these plants, “urushiol”, is present in the stems and fruits of both plants in all seasons and is capable of causing the typical rash.

Master Gardeners are often asked to identify a plant as to whether it is poison ivy. There are several plants that may have three leaves or other characteristics causing confusion with poison ivy and poison oak. Some plants often having three leaves are bladdernut shrub, boxelder tree sprouts, aromatic sumac, skunkbush sumac and wild blackberry. Other plants that may form vines and can be confused with the poisonous ones are Virginia creeper (five leaves), wild grape and Boston and English ivy.

Garden tips

§  Now is a good time to fertilize spring-blooming bulb plants. Use only nitrogen unless a soil test indicates a need for phosphorus and potassium. If you are not sure where the plants are, wait until spring and fertilize when the leaves first emerge. These plants' root systems are inactive from bloom time in spring until the following fall. Fertilizing them at that time will result in waste.

§  Dig and store tender perennials like dahlias and caladiums in a cool, dry location. Cannas and elephant ears can also be dug, but most will survive the winter fine if mulched heavily and in a sheltered area.

§  Plant fall mums and asters and keep them watered during dry conditions. Don’t crowd because they take a couple of years to reach maturity.