HARDINESS: Zones 3 to 8
PREFERRED SOIL pH: Neutral
PREFERRED SOIL TYPE Rich, moist
PREFERRED LIGHT: Full to partial shade
ATTRIBUTES: Fragrant spikes of white flowers in summer; neat clumps of lacy foliage
SEASON OF INTEREST: Spring through fall for foliage; summer to fall for flowers
FAVORITES: C. simplex 'White Pearl'; C. racemosa 'Brunette'; C. ramosa, the species
QUIRKS: C. racemosa flowers have a scent that is more musky than fragrant
GOOD NEIGHBORS: Astilbe, Japanese anemone, ferns, hydrangeas
WHERE IT GROWS BEST: Moist soil in shade
POTENTIAL PROBLEMS: Rust
RENEWING PLANTS: Plants live for decades; rarely needed; if so, divide in early spring
CRITTER RESISTANCE: Excellent
SOURCE: Bedding plants, division
DIMENSIONS: In flower, 3-7 ft (1-2.1 ml tall and 3 ft (1 m) wide
Cohosh in the Landscape
Cohosh is a plant with several common names, including bugbane and snakeroot, which reflect ancient uses of the root as an insect repellent and snakebite antidote. But nothing describes the plant's ornamental virtues like another of its names: fairy candles, which refers to its tall, graceful wands of creamy white flowers, visible even in twilight.
A true shade lover even in areas with cool summers, cohosh forms bunches of feathery foliage reminiscent of parsley, standing about 2-4 ft (0.6-1.2 m) tall. From midsummer through fall, it sends up tall, fragrant, bottlebrush-shaped flower spikes. A mature cohosh in full bloom can tower 5-7 ft (1.5-2.1 m). Station this plant at the entrance of a woodland garden or use it to flank a shaded gateway. It is especially handsome in tandem with astilbe and Japanese anemone. If you crave high drama, put cohosh in a spot where the flowers will be backlit by the setting sun, making the "candles" blaze.
At only 3 ft (1 m) tall, Cimicifuga simplex 'White Pearl' is relatively compact. It has handsome green leaves and fragrant fall flowers on arching stems. C. ramosa, which reaches 5 ft (1.5 m), has sweet-scented white flowers in late summer. Several cultivars, such as 'Brunette' and 'Hillside Black Beauty', start with burgundy leaves that fade to green as the season progresses. These cultivars need a few hours of sun each day to maintain the maroon pigment, which also appears in the flowers, giving them a pink cast. C. racemosa is one of the tallest species and blooms ahead of other species, in summer. Its flowers have a musky scent that some people find unpleasant.
Although cohosh grows wild in areas with moist soil, it will thrive in average garden conditions in cool regions once established. However, the plant can be a challenge in hot-summer areas, where the burgundy-leaved cultivars can be especially problematic when exposed to the few hours of sun they need to maintain their coloring. It's generally best to grow these plants where they'll receive afternoon shade.
It's advisable to amend soil with abundant organic matter before planting. This very hardy perennial forms large, impressive clumps over the years, which need division only about once a decade. To increase your collection, dig and divide cohosh early in spring.The first year after dividing, however, flowers may be sparse.
True to its name of bugbane, these plants are rarely bothered by pests. Red-orange spots on leaves may indicate a disfiguring fungal disease called rust. If this occurs, clip and destroy affected foliage and thin surrounding plants to improve air circulation.