Getting it to bloom

Why won't my Blue Cohosh bloom? (and how to make it flower)

Also called Blue Cohosh, Papoose Root, Squaw Root, Blue Ginseng (Caulophyllum thalictroides).

More about blue cohosh

About Blue Cohosh

Caulophyllum thalictroides · also called Blue Cohosh, Papoose Root · flowering

A graceful North American woodland native in the Berberidaceae family, known for its blue-green, thalictrum-like foliage and small yellow-green to brownish-purple flowers in early spring, followed by striking bright blue, berry-like seeds. Growing 30–90 cm tall in cool, moist shade, it is a slow-colonising perennial for naturalistic woodland gardens. The whole plant is toxic.

Plant type: flowering

Watch for — Slow Establishment and Spread: Blue cohosh is very slow-growing; plants may take 3–4 years to reach flowering size from division. Seed germination requires warm stratification followed by cold stratification (double dormancy) and can take 18+ months. Patience and site preparation are essential.

The reasons blue cohosh isn't blooming

Almost every non-blooming blue cohosh traces back to one of these, roughly in order of how common they are:

Too little sun — most of these need full sun (or very bright light) to flower well; shade gives leaves, not blooms.
Too much nitrogen feed, driving lush foliage at the expense of flowers (very common with general or lawn feeds).
The plant has not been deadheaded, so it stops flowering once it sets seed.
Irregular watering — drought or waterlogging at the budding stage makes buds abort.
It is still too young or was checked by a transplant and is rebuilding before flowering.

Feeding blue cohosh a high-nitrogen general feed and growing it in too little sun — you get a big leafy plant and almost no flowers.

The fix — how to get blue cohosh to flower

Maximise sun. Give blue cohosh the sunniest spot you have — for most bedding and fruiting plants, more direct light directly means more flowers.
Switch the feed. Move off high-nitrogen feeds and use a higher-potassium "bloom" or tomato-type feed as it comes into flower.
Deadhead regularly. Remove spent flowers often to keep it producing more rather than stopping to set seed.
Water consistently. Keep moisture even through budding and flowering — drought-then-flood swings make buds drop.

Light and feeding do most of the heavy lifting here. Dial in the spot with the light guide for blue cohosh and get the feeding right with the blue cohosh fertilising schedule — the wrong feed (too much nitrogen) is one of the most common silent reasons a healthy plant makes leaves instead of flowers.

Bloom season and what to expect

Blue Cohosh flowers across its growing season (mostly summer) and, kept fed and deadheaded, can bloom for many weeks or right up to frost.

Post-bloom care so it flowers again

Deadhead, keep feeding lightly, and many will rebloom; collect seed from the best plants at the end of the season if you want to grow them again.

For everything else this plant needs day to day, see the full blue cohosh care brief and its watering schedule — a stressed, badly watered plant rarely has the energy to flower at all.

Blue Cohosh blooming — frequently asked questions

Why won't my blue cohosh flower?

Blue Cohosh blooms on the season's growth given enough sun, warmth and the right feed — there is no cold or photoperiod trick, just good growing conditions and a bloom-leaning feed. The most common reason it is not happening: Too little sun — most of these need full sun (or very bright light) to flower well; shade gives leaves, not blooms.

How do I make blue cohosh bloom?

Give blue cohosh the sunniest spot you have — for most bedding and fruiting plants, more direct light directly means more flowers. Move off high-nitrogen feeds and use a higher-potassium "bloom" or tomato-type feed as it comes into flower.

When does blue cohosh normally bloom?