Valued for its attractive, blue-green foliage and bright blue fruits, this member of the Barberry family is a long-lived beauty that thrives in shade. The elegant, many-stemmed perennial herb grows up to 3 feet tall and flaunts a generous network of thrice-divided leaves that emerge with purple highlights from purplish-green shoots in early spring. Young plants are covered with a waxy bloom. Before the leaves unfurl, yellow clusters of diminutive, star-shaped flowers appear above the foliage. Each petal has a fleshy nectar gland that is visited by early solitary bees. Erect clusters of green, circular fruits follow in summer, maturing to blue and persisting through cold weather as a delightful contrast to winter’s brown leaves. The berry-like seeds provide sustenance for birds, but they shouldn’t be eaten by humans. Blue cohosh flourishes in dappled sunlight and partly to deeply shaded woodlands with fertile, loamy soil containing organic matter from decaying leaves and plants. Gardeners can imitate this natural method of fertilizing by spreading leaves around the base of the plant. Floral Encounters, an organic seed farm, cautions that blue cohosh will not grow under conifers and may take 2 to 3 years to flower. Individual plants are not self-fertile, so several plants are necessary for fruit production. Blue cohosh spreads slowly by rhizomes to form colonies and the seeds are difficult to germinate, so the speediest route to propagation is to divide and transplant the rhizomes just after flowering. (The lumpy rhizomes are responsible for the common name, “cohosh,” which means “rough” in Algonquin.) Handle blue cohosh with care and gloves as the leaves detach easily and contain toxins that may cause skin irritation. Those same toxins, however, are poisonous and distasteful to deer and other mammals, making this a desirable plant for areas heavily populated with deer. Blue cohosh is mostly disease and pest free.
This native of eastern and central woodlands of the US is common throughout Ohio. A similar species, giant cohosh, has purplish flowers with styles twice as long as those of blue cohosh. Giant cohosh blooms at a different time, and its native range is further north. The unusual stems and leaves of blue cohosh inspired the scientific name: the species name reflects the similarity of blue cohosh’s foliage to that of meadow rues (Thalictrum spp.), and the genus name is derived from the Greek words kaulos, meaning “stem,” and phyllon, meaning “leaf.” Two additional common names--squaw-root and papoose-root—most likely originated from the traditional practice of using blue cohosh to treat pregnancy and labor issues.
Native habitats include deciduous and mixed woodlands, moist coves, floodplains, and hillsides. Cohosh is ideal for naturalized areas, woodlands, and shade gardens.
Grows 1-3’ tall and 6-12” wide.
Prefers dappled light and tolerates full shade.
Prefers rich, average to moist, well-drained soils, including sandy and silty.
Tiny, purplish-brown to yellow-green flowers are in loosely branched cymes from April to May. Each 3” cluster has about 5-30 flowers. Tiny, fan-shaped nectar petals reside at the base of 6 longer sepals. A stamen lines up with each sepal and petal. Each flower produces 2 seeds with fleshy seed coats that turn from green to blue. The ovary is ruptured by the developing seeds, which is uncommon among flowering plants. Uneaten seeds harden and remain on the plant.
Non-flowering plants produce a single compound leaf under the inflorescence at the top of the stem. Flowering plants produce a second leaf at the middle of the stem. Each compound leaf is divided into a whorl of 3 compound leaflets that are divided into egg-shaped, 1-3” subleaflets arranged in groups of 3. The surface of the leaflets is smooth and green and the margins are entire. The upper compound leaf has smaller leaflets than the lower leaf.
Cylindrical stems are unbranched, smooth, erect, and light green to pale purple.
Host plant for 3 species of moth larvae, including snowy geometer, black-patched clepsis, and Norman’s quaker. The flowers are pollinated by various small flies, parasitoid wasps, and small bees. Birds and mice eat the berries.
Medicinal, Edible, and Other Uses:
Native Americans and European herbologists and midwives used blue cohosh to induce labor and menstruation. Blue cohosh is not related to black cohosh, but both have been used to treat women’s health issues.
Blue cohosh was used in the US in the early 20th century by Eclectic physicians (those who use natural remedies) to treat kidney infections, arthritis, painful periods, and other ailments. It was a major ingredient in a popular preparation called Mother’s Cordial. Because some of its compounds have deleterious effects when used improperly, it’s best to work with a certified herbalist.
Caution: Seeds and roots have low toxicity levels, but raw seeds are toxic to children. The berries, roots, and leaves may cause skin irritation if touched.
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