The rhyme, “Leaves of three, let me be” helps identify poison ivy.

The rhyme, ‘Leaves of three, let me be’ helps identify poison ivy.

Soon the poison ivy season will be upon us, and so it behooves us to know something about this native vine. Poison ivy is neither ivy nor does it have poisonous leaves. Urushiol, the oil found in poison ivy is an allergen, not an irritant — humans are the only creatures allergic to urushiol.

Scientists believe that poison ivy originated 80 million years ago when dinosaurs inhabited the earth. When land temperatures were warmer than they are now, poison ivy migrated across the Bering land bridge into Asia where it evolved from a vine into the Japanese and Chinese lacquer trees.

Entranced with its fall color, John Tradescant, the English naturalist and plant collector, brought it back to England in 1632. Later it was used to help stabilize the Dutch dykes and now is slowly migrating to the Black Forest.

Toxicodendron radicans typically is a hairy vine that can reach 75 feet in length and 6-7 inches in width. It is the hairs that enable it to cling to trees. The three, lobed leaves emerge in the spring with the flowers appearing in the early summer. The resultant berries, so popular with birds, are toxic to humans. Since plants must be at least of three years in age to bear flowers, it is important to get rid of the ivy before birds spread it.

It is our immune system that is responsible for the terrible itching and lesions resulting from contact with urushiol. Typically, the initial contact will not cause a reaction, which is the reason most children younger than the age of 5 rarely get the rash. Further contacts create a sensitivity that typically appears with greater severity with each contact.

This allergy differs from other allergies in several respects. Approximately 85 percent of the population is allergic to urushiol whereas only 20 percent of the population suffers from standard allergies. Many urushiol dermatitis sufferers do not have other allergies while those with standard allergies typically have more than one allergy; and those who are immune to urushiol may have children who are highly susceptible to it, unlike standard allergies that typically have a hereditary component. Interestingly, those who get hives or eczema rarely seem to have an allergic reaction from urushiol contact.

Urushiol penetrates the skin’s surface in 10-20 minutes so speed is of the essence. Washing with a strong soap helps those who are moderately sensitive to it. Experts now seem to recommend using a laundry detergent dissolved in cold water. Why cold water? Warm water opens up the skin’s pores. Some believe rinsing the area in cold water is as effective as washing with soap.

The rash will last 14-21 days. Many people use calamine lotion as it momentarily relieves the itching as does using very hot water. Prescription cortisone creams are effective if used early, but those with extreme sensitivity should go for medical help. There are barrier creams that provide some protection up to four hours and while they cannot block out all of the urushiol, they can reduce the severity of the rash.

Urushiol remains on poison ivy throughout the year, even when the plants are dormant or dead. It also can remain on clothing after washing because it isn’t water-soluble.

So how does one get rid of this scourge? First, put on a urushiol-blocking cream and completely cover yourself up. Glyphosate will kill poison ivy from the late spring to the middle of fall when temperatures are warm. For the early spring there are other chemicals, such as Ortho’s Poison Ivy and Poison Oak Killer. It will take poison ivy seven to 10 days to die. Remember, it still contains the urushiol so it’s important not to burn it. If chemicals aren’t your thing, hire a herd of goats as they love the foliage and the urushiol will not appear in their milk.

It’s OK to curse this native plant. Just remember that it has existed for 80 million years — and like the cockroach and earthworm will undoubtedly out-survive us.

Absent from their gardens, Kit and Lise enjoy roaming our region exploring the intersection of horticulture and suburban living. More on Instagram @AbsenteeGardener or email

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