October Nature Almanac: Poison Ivy Can Brighten or Blighten Your Day
By Ruth Carol Cushman with Stephen R. Jones and Scott Severs
October 2022
Beautiful autumn leaves of poison ivy. Photo by Glenn Cushman.
One October an innocent young friend of ours picked a bouquet of autumn leaves and mailed them to her parents in Japan. She ended up in the infirmary, but fortunately, her parents were warned in time: poison ivy—don’t touch.
Poison ivy (Toxicodendron rydbergii) with its variegated shades of salmon, orange, red, and yellow is one of the most beautiful autumn plants in the understory. It’s no wonder hikers are tempted to collect leaflets of three from this stunning member of the sumac, or cashew, family Anacardiaceae.
Clumps of whitish berries persist throughout the winter and are eaten by woodpeckers, warblers, vireos, Cedar Waxwings, and other birds. Deer, black bears, muskrats, chipmunks, rabbits, and many reptiles and amphibians eat all of the plant parts with no adverse reactions and use the thickets as shelter. In spring, pollinating insects — including bees, ants, wasps, and butterflies — visit the clusters of small off-white flowers. Primates, it seems, are the only animals to suffer from its touch.
We’ve read that some folks nibble a small amount of the leaves in spring to develop immunity to the itchy rash that follows contact. We do NOT recommend that. Instead, if you touch the plant, wash with cold (not hot) water and apply a cortisone cream or calamine lotion. Mayo Clinic suggests you can also take an oral antihistamine and soak the affected area in cool water containing half a cup of baking soda. The rash usually lasts about ten days. To avoid infection, don’t scratch the blisters, but do see your doctor if the blisters become infected.
Poison ivy is not actually poisonous. Instead, it contains urushiol, an irritating oil that causes an allergic reaction in many people, although some folks have a natural immunity to it. I thought I was immune until I spotted my first clump of Indian Pipes (a mysterious-looking white plant lacking chlorophyll that is sometimes called “ghost plant”), and knelt for a closer look. After several minutes of rapt adoration, I realized I was kneeling in a luxuriant bed of poison ivy. And, no, I was not immune.
Leaves of three, let it be. Poison ivy has several different growth forms so recognizing its leaves is an important identification step. Photo by Stephen Jones.
The mnemonic “leaves of three, leave it be,” a good adage for avoiding poison ivy. However, not all three-leaved sumac are an issue; three-leaf sumac (Rhus aromatica trilobata), a close relative, does not cause an allergic reaction. In fact, early settlers made a drink from the berries and called the shrub “lemonade bush.” Because the leaves are pungently aromatic, others call it “skunkbush.” The small red berries are relished by birds, though we prefer raspberries.
Smooth sumac (R. glabra), another relative of poison ivy, inspires us to make annual pilgrimages to the foothills to revel in ruby red leaves that glow like stained glass when backlit by autumn sunlight. Unlike the multi-colored poison ivy and three-leaf sumac, the leaves, though brilliant, are a uniform crimson. The dull red berries, high in vitamin C, are good survival food for wildlife. We surmise that the critters must regard them as we regard broccoli since uneaten fruits persist on the branches into late spring. To us, the berries are slightly bitter with a faint lemony taste and cause a scratchy sensation in the throat.
Poison ivy can grow to be as tall as a hiker! Photo by Glenn Cushman.
We go on long leaf-peeping trips into the mountains to admire aspen, and we walk around town to marvel at maples. Understory plants, however, are often overlooked. In October, these more modest shrubs come into their own glory.
You can see poison ivy and other vivid understory plants at:
A delightful red to view but not pluck.
Photo by Scott Severs.
Heatherwood Trail, beginning at the parking spot just south of the 75th Street bridge over Boulder Creek. The poison ivy patch along the path leading to the bridge is taller than many hikers!
Bluebell-Baird Trail, beginning in Baird Park south of the point where Baseline Road becomes Flagstaff Road. Look for poison ivy in the streambed near the start of the trail and for smooth sumacs higher up.
Mesa Trail, south end off of Eldorado Springs Drive. Poison ivy grows in the dry creek bed, and smooth sumac is especially dramatic along the section beyond the Doudy-Debacker-Dunn House and on the South Boulder Creek Trail that forks east 0.7 miles from the trailhead.
Other October Events
Black bears fatten up on wild fruits, raid unsecured garbage cans, and climb trees to nap. We recently encountered one sauntering up the Saddle Rock Trail munching on fallen apples.
Western rattlesnakes converge on communal hibernating sites in rocky hillsides and prairie dog colonies.
Bull elk bugle to attract harems along Plain View Road south of Boulder, at Caribou Ranch, and in Golden Gate State Park.
Bottle gentians, gumweed, and asters continue to bloom in the foothills.