Poison ivy is usually a problem in spring, summer and fall, although you could come in contact with the dried winter leaves and get enough of the toxin to cause the disease. If you live in a warm climate, you could conceivably get poison ivy all year long. It is important to know what a poison ivy plant looks like so that you don’t accidentally walk through a patch of it. Similarly, you should know what poison oak and poison sumac look like so you don’t get poison oak or poison sumac.

Poison ivy is also called Toxicodendron radicans and is a plant that grows in temperate climates. When it grows it grows to be about one to two feet off the ground and the leaves are green in color when it is summertime. The leaves are an ordinary elongated leaf shape that comes in clusters of three to a branch. When you see that classic cluster of three leaves, assume it is poison ivy and stay away from it.

In the fall, the leaves turn brown like any other leaf but it can still be toxic. The toxin is an oily substance that can survive in colder climates. Stay away from the leaves, even if they are brown. Use gloves if you are trying to remove the plants from an area and wash the gloves right after you use them so you don’t get the oily toxin on your body.

Poison ivy needs to be distinguished from poison oak, although they both can give you a rash. In fact, poison ivy, poison sumac and poison oak all contain the same toxin called urushiol. This is the oily substance that your body comes in contact with and gives you the rash. Poison oak also comes in three leaves with the middle leaf coming on a bigger stalk. Poison ivy is similar to poison oak although poison oak can grow taller than poison ivy.

Poison sumac has leaves in a row of paired leaflets with a leaflet at the end of the stalk. The leaves of poison sumac often have black splotches on it that contain heavy amounts of urushiol. This is what happens when the urushiol comes in contact with the air.

Poison ivy can grow in a vine form, so be wary of three-leaved vines. Poison oak is a shrub that has leaves that are oak-like but that come in threes as mentioned. Poison sumac can also be a small tree-like plant or can be a shrub. All of the leaves of these plants turn yellow or red in the fall before turning brown.

The urushiol can come in contact with your skin and can cause a rash within seconds of touching the plant. This is why you should stay away from the plant altogether. It takes about 12-72 hours before the allergic reaction to urushiol begins and the severe itching, redness, localized swelling and blisters begin to show up. The spread of the rash comes when you itch the rash or can spread because it is an allergic reaction that often spreads anyway.

Katie Hoffman is a certified master gardener. She writes about garden decor and garden stepping stones.