Black cohosh's huge, wispy spires of star-like flowers create a magnificent display for three weeks beginning as early as May and as late as August. The pure-white wands illuminate shaded woodlands like fairy candles, which is another common name given to this native of eastern North America. The blooms emit a sweetly fetid odor that attracts flies, gnats, beetles, and bumble bees. Each flower is replaced by a small, round follicle that splits open to release seeds. One of the largest woodland wildflowers, black cohosh grows 4 to 6 feet tall with handsome, deep-green, astilbe-like foliage that adds color and texture throughout the growing season. It thrives in rich, moist, well-drained soils in full to part shade, ideally with 2 to 3 hours of morning sun. This slow-growing plant is a great choice for naturalizing large, lightly shaded areas or for filling in spaces after spring ephemerals have gone dormant. It may take several years to establish and flower. Plant in an area protected from strong winds.
A member of the Buttercup family (Ranunculaceae), black cohosh is also known as bugbane and black snakeroot. Actaea is the ancient Greek name for elderberry (it’s unclear as to why Linnaeus might have used that name), and racemosa refers to the elongated inflorescence. The plant is well known for its medicinal uses. It contains chemical compounds that are anti-inflammatory and anti-rheumatic, and it’s often used to treat women’s issues. It’s approved in Germany for treating menopausal symptoms.
According to naturalist Mary Anne Borge of The Natural Web blog, “Black cohosh is the only food Appalachian azure butterfly caterpillars can eat. Female butterflies lay their eggs on flower buds. When the caterpillars hatch, they begin eating the buds and flowers, moving on to leaves if no flowers remain. Like the other azure butterfly caterpillars, the Appalachian azure caterpillars are protected by ants in exchange for the delicious honeydew the caterpillars excrete.” (https://the-natural-web.org/2016/07/24/who-uses-black-cohosh/). Ms. Borge also writes that black cohosh has evolved a strategy of offering pollen, but not nectar, to potential pollinators. While most pollen is eaten by pollinators, the insects unwittingly transfer about 2% to other flowers. Black cohosh’s pollen and unusual fragrance attract numerous insects whose bodies carry pollen to the stigmas of flowers on other black cohosh plants.
Black cohosh is susceptible to getting leaf spot or root rot diseases. Don’t let the plants get too crowded, and avoid planting in areas with poor air circulation. To propagate, divide the rhizomes in early spring or late fall. Black cohosh is generally not eaten by deer.
Native habitats include moist, deciduous woodlands; ravines; and slopes. Plant with ferns, wild ginger, mayapple, and other low-growing woodland groundcovers. Use in shady cottage or rain gardens or as a vertical accent in the back of borders. Seed heads are often used in flower arrangements.
Plant Characteristics:
Grows 4-7’ tall and 2-4’ wide.
Prefers full or light shade and morning sun.
Prefers moist, well-drained soils, including clay, loamy, and sandy.
Hundreds of tiny, petalless, fluffy-looking flowers in 1-2’, wand-like cluster bloom from the bottom of the flower stalk to the top. Numerous stamens surround a white stigma. Flowers give way to small, dry seed pods from July-September.
Basal leaves are up to 3’ long and broad with repeated sets of tripinnately compound leaflets. Terminal leaflet is often three lobed. Obovate leaflets have 2-5 lobes and toothed or incised margins. The long flower stem is green to purplish.
Wildlife Value:
Host plant for larvae of spring blue, holly blue, and Appalachian azure butterflies. In addition to bumble bees, pollinators include sweat and leaf-cutter bees, syrphid flies, tumbling flower beetles, and longhorn beetles. Resistant to deer.
Medicinal, Edible, and Other Uses:
Native Americans used black cohosh for a variety of conditions ranging from gynecological problems to rheumatism to snake bites.
Nineteenth-century physicians used it to treat fever, menstrual cramps, and arthritis. Other traditional and folk uses were for treatment of sore throats and bronchitis.
Black cohosh has been used as an alternative to mainstream hormone replacement therapy for treatment of menopause and premenstrual syndrome (https://tinyurl.com/bdex7u98).