'Leaves of three, let them be...' Identifying poison ivy during the growing season is much easier than during the winter months.
Poison Ivy or Virginia Creeper? K-State horticulture expert explains the difference
Knowing how to identify poison ivy is key to avoiding contact
Jan. 14, 2021
MANHATTAN, Kan. – Most gardeners and outdoor enthusiasts have heard at least some version of the popular refrain to help them stay clear of poison ivy.
‘Leaves of three, let them be.’
The saying points out the defining feature of poison ivy; that is, three leaflets per leaf protruding from a vine and containing urushiol, an oil that causes a rash in most people.
During the growing season – typically spring and summer – poison ivy is easy to distinguish from the Virginia creeper, a vine with five leaflets. Virginia creeper does not contain urushiol and typically does not cause a rash.
“However, during the winter, distinguishing between the two vines can be more difficult because the leaves have dropped,” said Ward Upham, a horticulture expert at Kansas State University.
Poison ivy can still cause a negative reaction during the winter, so it’s important to be able to identify the vine without its’ three-leaflet clue.
“This is actually easy to identify once you know what to check,” Upham said. “Look at the aerial roots. On poison ivy, they are hair-like, but on the vine of the Virginia creeper they are more plump and about the size of a pencil lead.”
Upham noted that urushiol can cause a rash 1 to 5 years after a plant has died. The amount of urushiol that covers the head of a pin can cause a rash in 500 people, he said.
“Poison ivy can grow as ground cover, a shrub or a vine,” he said. “Using a chainsaw on poison ivy in the winter can release sap which makes a rash more likely. This is worse on warm days where there is more sap rise.”
Upham and his colleagues in K-State’s Department of Horticulture and Natural Resources produce a weekly Horticulture Newsletter with tips for maintaining home landscapes. The newsletter is available to view online or can be delivered by email each week.
Interested persons can also send their garden- and yard-related questions to Upham at wupham@ksu.edu, or contact your local K-State Research and Extension office.
