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Plants to Avoid When Spending Time Outdoors

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Warm weather means spending more time outdoors. But rash-causing plants can ruin your good time. By learning how to recognize and care for these nuisances, you can make sure everyone has a better time on your picnics, camping trips, and hikes.

Poison Ivy, Oak, and Sumac

Why it is harmful

Plants in the toxicodendron genus produce urushiol, a clear liquid that causes a rash in most people who touch it. (In fact, urushiol is the most common allergy in the US.) Keep in mind that the vines and stems are even more poisonous than the leaves. And stay away from old plants, which can remain poisonous for several years after they die.

Where it grows

  • Poison Ivy: Poison ivy is common in every US state east of the Rockies, as well as much of Canada and parts of Mexico. It thrives especially in suburban areas on the edge of woods.
  • Poison Oak: Poison oak actually refers to two different plants, Atlantic poison oak which grows in the Southeastern US from Virginia to Texas and Western poison oak which grows on the Pacific coast from southern Canada to Baja California in Mexico.
  • Poison Sumac: Poison sumac grows in the eastern US and Canada, exclusively in very wet or flooded soils. Be especially careful in swamps and bogs where poison sumac thrives as it is much more toxic than poison ivy and oak.

How to identify it

Look for clusters of three, almond-shaped leaves. (“Leaves of three, let it be”) The middle leaf has a visibly longer stem than the other two. (“Longer middle stem, stay away from them.”) Finally, vines of poison ivy and oak are ragged or hairy. (“Hairy vine, no friend of mine.”)

Poison Ivy

    • Poison ivy: Poison ivy grows as a vine and as a shrub up to about four feet tall. When you’re on vacation, keep in mind that there are many subspecies of poison ivy. Most of these plants still demonstrate the clusters of three leaves, longer middle stem, and hairy vines.

      Poison Oak

    • Poison oak: With clusters of three leaves and hairy vines, Atlantic poison oak looks much like poison ivy. Even though it isn’t related to the oak, Atlantic poison oak gets its names from its leaves, which look like oak leaves—small, round “fingers” or lobes coming from a central vein. Western poison oak looks different depending on where you are. Watch for vines with oak-like leaves and ask a local to show you a sample before hiking in a new place on the West coast.

      Poison Sumac

    • Poison sumac: Unlike poison ivy and poison oak, poison sumac grows only as a shrub or small tree. It grows up to 30 feet tall. The 2-4 inch leaves are oval and come to a sharp point.

How to treat it

If you notice that you’ve touched a toxicodendron plant, wash the area with warm soap and water and soon as you can. The rash itself isn’t contagious, but you can spread urushiol from one body part or person to another as long as it lingers on your skin. You can treat rashes with calamine lotion or Burow’s solution, though many dermatologists recommend simple home remedies like oatmeal baths or baking soda. Mix a cup of oatmeal ground in a food processor or half a cup of baking soda into a tepid bath to offer some relief. Keep in mind that some people are highly sensitive to poison ivy, so see a doctor right away if your eyes swell shut or you develop large, painful blisters.

Stinging Nettles

Why it’s harmful

Stinging nettles are useful—for textiles, medicine, and even food—and ecologically important. Even so, the hollow hairs or trichomes of stinging nettles inject histamine into whatever touches them. Though histamine isn’t a poison like urushiol, it causes a stinging itch.

Where it grows

Stinging nettles are especially common in northern Europe, but you can find them in Europe, Asia, northern Africa, and North America. Nettles especially thrive around abandoned buildings.

Stinging Nettles

How to identify it

Stinging nettles grow 3 to 7 feet tall in the summer. The soft green leaves are 1 to 6 inches long and are serrated like the edge of a bread knife. The leaves and steams look hairy because of the needle-like trichonmes that release histamine when touched.

How to treat it

Treat stinging nettles with anti-itch creams like antihistaminics (Benadryl). You can also look for dock leaf growing near stinging nettles—squeeze the leaves until a green liquid comes out before rubbing the liquid onto the nettle stings.


Why it’s harmful

Ragweed causes about 75% of pollen allergies in the U. S. But it can also cause a raised, red, itchy rash that lasts from 1 to 3 weeks. Unlike toxicodendron plants and stinging nettles, you don’t have to touch ragweed to develop a rash.

Where it grows

Ragweed grows in temperate regions all over the Northern Hemisphere and in parts of South America. Look for it in sunny, grassy areas.

How to identify it


Common ragweed grows to a height of about 3 feet. The leaves are grayish to silvery green. They are bipinnatifid, meaning the leaves look like they are made of many smaller leaves. It is easiest to recognize ragweed after it has been fertilized so that long, skinny clumps of very small flowers grow out of the top. There are 41 different species of ragweed worldwide, many of which cause allergic reactions. Be sure to find out what ragweed looks like in areas where you’ll be spending time outdoors.

How to treat it

Wash the area with lots of water to remove any ragweed pollen from the skin. For severe itching or rashes that won’t go away, you may need a corticosteroid cream to clear up irritation—see a doctor.

Before you spend time outdoors somewhere new, check out a field guide for information about dangerous plants nearby.

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