September Is The Time For Prairie Dock To Shine

Aug 31, 2023 ● By Sheryl DeVore

Photo by Steven D. Bailey

When European settlers came to what is now the Chicago region, they encountered an unusual plant with huge, spade-shaped leaves at the base of the plant and a slender green stalk rising above their heads. Called prairie dock, it’s one of the longest-lived species in the prairie, and September is its time to shine. “In the prairie or the garden, it’s the star,” says Pam Karlson, who recently planted prairie dock in her bird-friendly Chicago backyard garden.

One plant can be a specimen in the garden. A mass gathering of them in a large space, including prairies and grasslands, can be the most noticeable plant in late summer as its multiple yellow flowers rise eight feet in the air at the top of the stalk, looking like suspended stars.

Prairie dock mostly grows in Illinois, Indiana, Missouri and Wisconsin. It’s the last species of the native Silphium family to bloom in summer. An earlier bloomer is the compass plant, which also has long, tall stalks with yellow multi-petal flowers. But the compass plant has completely different leaves. They also arise from the base of the plant, but are deeply lobed and look almost like an extra-large pin oak tree leaf.

The compass plant species name, laciniatum, comes from Latin, meaning deeply cut, referring to its leaves. The species name terebinthinaceum for the prairie dock means “like turpentine”, and some say that’s what this plant smells like, referring to the resinous sap both prairie dock and compass plant exude. Botanists recommend not ingesting any part of prairie dock or compass plant because the species may be toxic to humans.

Both compass plant and prairie plant have sandpaper-like leaves that help the plants deal with drought. The roots can extend 10 feet or more below the soil, reaching to the water table, also helping them deal with dry conditions. Both species orient in a north-south direction, which gains maximum sunlight for photosynthesis and minimizes water loss due to transpiration, according to the U.S. Department of Agriculture. “In-mid summer, the leaves feel cool to the touch,” writes author Christopher David Benda in his prairie plant species accounts on the department’s website. Compass plants begin blooming earlier than prairie dock, but even in September, a few may still hold their flowers.

Cup plant leaves are arranged to gather water, which attracts thirsty birds on hot summer days. Photo by Steven D. Bailey.

Karlson has grown another Silphium species called cup plant (Silphium perfoliatum) in her yard for at least 20 years. This plant has large leaves going up the stalk, with two forming a cup where rainwater gathers. Karlson says cup plants begin blooming in July and often extend into September. “I’ve heard of cup plants taking over a garden, but it hasn’t in our yard,” she says. What it has done is give her lovely experiences. “Several years ago, I watched a yellow warbler drinking water from the plant. It was really cool.”

However, she notes, “Our stand of cup plants did jump to a spot behind our fence that borders the alley. That stand has gotten pretty large and looks lovely, brightening up the alley and peeking over our fence in bloom. One of the benefits of it growing there is that it has tremendously helped the flooding issue in the alley.”

She decided to experiment and grow prairie dock this season. “I saw it in a native plant garden walk in Oak Park. I’ve been admiring how the plant grows. It’s cool and interesting. I think it will be a really interesting statement in a garden,” Karlson relates after purchasing a small, one-gallon pot of prairie dock from a nearby garden shop that sells native plants. She planted it in a sunny spot, a requirement for growing the Silphiums.

Prairie dock blooms at Grant Woods Forest Preserve in Lake County. Photo by Steven D. Bailey.

The gardener that wants to plan prairie dock needs to be patient. As John Hilty writes in Illinois Wildflowers, “Prairie dock is rather slow to develop, but it is very reliable and nearly indestructible at maturity.

Botanist and retired director of field surveysfor the Illinois Natural History Survey

Randy Nyboer transplanted a small prairie dock about eight years ago into his native prairie garden in Morrison. It started out as a six-inch-long, pencil-like root. In August 2022, it began blooming. “It has skyrocketed to a nine-foot cane. The leaves are huge,” he says.

Rewards for growing prairie dock include watching the many pollinators it attracts, including bumblebees, monarch butterflies and even hummingbirds. “Goldfinches also love prairie dock,” says Arlene Doran, a member of the Gardeners of Central Lake County. She has watched goldfinches in fall eating the seeds where she planted prairie dock at a beach in Mundelein. “It’s been a little happy there,” says Doran, who has thinned some of the plants and thrown some stalks with seeds near a ravine in her backyard. “Now I have prairie dock,” she says. “Each year by the end of August, they start blooming.” Tossing prairie dock seeds in a yard doesn’t work for everyone,” she cautions. “Gardeners will discover what works and doesn’t work in their yards when it comes to planting the silphium species.”

Prairie dock has been planted by Chicago region park districts and managers of natural areas and forest preserves to give visitors a taste of what settlers saw centuries ago. For example, Park No. 540 at 24th and Federal Street, in Chicago has a natural area that runs along the park’s southern and western borders. The Chicago Park District has planted native wildflowers that bloom throughout the seasons, beginning with golden Alexander in late spring and ending with prairie dock in late summer.

Sheryl DeVore has written six books on science, health and nature, as well as nature, health and environment stories for national and regional publications. Read more at SherylDeVore.Wordpress.com.