Black cohosh

Questions about black cohosh

Does black cohosh need sun or shade?

Black cohosh grows in part sun (4 to 6 hours of sun, including some afternoon sun), part shade (2 to 4 hours of sun, mostly in the morning) and shade (less than 2 hours of direct sun, or bright dappled light).

It wants soil that stays evenly moist, rich in organic matter, and a good soak in dry spells.

What zones does black cohosh grow in?

USDA zones 3 to 8. It is hardy to zone 3, which means it survives winter nights down to about −30 °F (−34 °C).

Above zone 8 it struggles: the zones measure winter cold, but a plant's top zone usually means the summers are too hot or the winters too mild for it to rest.

Gardening in Canada? Use the USDA zone for your town: Canada's own zone map uses different numbers.

When does black cohosh flower in my zone?

In zone 5 it flowers early July to early August. As a summer flower it moves about half a week for every zone: earlier where it is warmer.

Worked out from Hopkins' bioclimatic law: spring arrives about four days later for each degree of latitude north, and one zone is roughly two degrees. A warm spring or a cold one moves any garden two weeks either way.

How far apart should black cohosh be planted?

2½ ft (75 cm) apart, from the middle of one plant to the middle of the next. That is about its full width, so each plant keeps its own outline.

It grows 5 ft (150 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.

How many black cohosh plants do I need?

At 2½ ft apart, set out in staggered rows:

• 2 to fill 10 square feet (about 1 m²)
• 5 for a single row 10 ft (3 m) long
• 6 to fill a 4 × 8 ft bed on its own

In a mixed border, plant it as one at a time, repeated along the bed at intervals; a slender one reads better as a clump of three.

In the bed above, the planner used one in one group.

Is black cohosh poisonous?

Yes: mild toxicity to people. Eating the plant in quantity can cause nausea and dizziness.

Rated from NC State Extension. Where references disagree, the more cautious rating is used.

Do deer eat black cohosh?

Mostly not. NC State lists it as resistant to deer. No plant is proof against a hungry deer in a hard winter, but this one is low on the menu.

What flowers after black cohosh?

Black cohosh is over by early August. These start as it finishes and carry the same spot on, so it never goes flat:

• Tiger lily: from late July to late August, 4 ft tall.
• Japanese anemone: from mid August to early October, 3 ft tall, to stand in front of it and cover its fading stems.
• Lilyturf: from early August to mid September, 16 in tall, to stand in front of it and cover its fading stems.

What does black cohosh look like in winter?

Black cohosh dies down, but leave the stems standing: the seed heads stand through the winter, and songbirds eat the seed. Cut them down in early spring, before the new shoots come.

Is black cohosh good for bees and butterflies?

Black cohosh is visited by pollinators, butterflies, hummingbirds and songbirds.

It is a host plant: the caterpillars of spring azure and appalachian azure feed on its leaves. A butterfly can only lay its eggs on its host plants, so these do more for it than any nectar flower.

It is native to the United States and Canada.