Perennial cornflower
Centaurea montana
Also called Mountain knapweed, Centaurea and Perennial bachelor's button
Garden plant · PerennialsIt runs. Not viciously, but a three-year-old clump will be twice the width you planted and the middle will have gone bare — lift it, pull the good outer pieces off and throw the centre away.
Care at a glance
- Ease
- Easy
- Water
- Every 8 daysWater the ground — water at the base, in the morning, not over the leaves.
- Light
- Full sun to part shade
- Feed
- Not needed
- Humidity
- Average
- Hardiness
- Very hardy RHS H7, to -25°C
- Size
- 0.45 m tall · 0.6 m across
- Lifecycle
- Perennial
- Origin
- Mountains of Europe
Is it safe for pets and people?
No animal-poison authority lists this plant either way.
Nobody has checked this one against a source for us yet, so treat it as unknown rather than safe.
ASPCA lists three other Centaurea — cornflower as non-toxic, and yellow star-thistle and Russian knapweed as toxic to horses. Nothing is listed for this one, and a genus that disagrees with itself cannot answer for a species it does not name.
Checked against ASPCA and RHS on 2026-09-22. Where a source says nothing, we say nothing.
A guide, not veterinary or medical advice. If a pet or a person has eaten a plant and you are worried, call your vet or doctor now — don’t wait for signs to appear. Spotted a mistake? Tell us.
First signs of trouble
- White dust over the whole clump straight after the first flush is cut back, on the soft new leaves rather than the old ones.Powdery mildew · disease
- A three-year-old clump is a ring: flowering growth all round the edge and dead thatch in the middle, and it is twice the width you planted.Bare centre · disorder