The Number One Plant to Avoid Outdoors

By Keith Roumfort, Program Manager, Bridging the Watershed

“Three leaves, let it be.”

“Hairy rope, don’t be a dope.”

Such mnemonic sayings help people avoid one of the concerns for the average hiker: poison ivy. Poison ivy, a North American native that isn’t a true ivy, likes to grow in disturbed areas. Despite its name, it’s not poisonous, but the urushiol oil that lies in
plant gives humans an unforgettable rash.

To avoid that itching experience, it’s a good thing to know how to spot this common plant on outdoor trails.

Look at the edges (margins) of the leaves
Poison ivy has compound leaves, a cluster of three leaflets that form the leaf stemming from a petiole (“leaf stem”). Many other similar plants have compound leaves of three leaflets as well, so to help identify the plant, you can look at the edges or margins of the plant as well as counting leaflets.

Plant leaves are usually symmetrical, a mirrored image on both sides. Poison ivy’s margins on the leaflets can be symmetrical and asymmetrical on the same plant.

poison ivy margins
The margins can be smooth (entire) or jagged (toothed).
poison ivy symmetry


Fall Changes
Throughout fall, clustered berries ripen from green to a pale, light yellow. Often the seed-containing berries are gobbled up by birds before winter sets in. The leaves are deciduous, turning yellow or sometimes red before falling to the ground.
poison ivy berries 1
poison ivy berries 3


The Perennial Hairy ‘Rope’
No matter what the season, but especially during bare winters, the vines are easily visible. The vines may creep over the ground, on walls, and up trees. As the vines mature, they get thicker and covered with dark hairy-like structures that anchor the vine to the surface. Beware as the vines may give you the rash.
hairy rope 1hairy rope 2


Tips to remember if you are exposed:

  • Don’t infect your eyes or mouth as urushiol oil can spread the rash internally.
  • Don’t burn poison ivy because you can inhale the rash-inducing smoke.
  • Wash the exposed skin with plenty of cool water without the water getting to other areas of your body. Warm or hot water can open up your pores to the oil. Be careful in removing exposed clothing and cleaning it.
  • A person with a rash is not contagious. The urushiol oil has already been absorbed into the skin. Only contact with residue oil can spread the rash.
  • If the rash gets worse and/or lasts for a few weeks, see a doctor.

Spending time outdoors can be lots of fun no matter what the activity with just a bit of common sense and precaution. Some people may claim to be immune to poison ivy, but like other forms of immunity, it can be lost. The best way to prevent the itchy surprise after a hike is to be aware of where you are walking and develop sight recognition of poison ivy.

Comments are closed.