Troubleshooting
Cosmos problems — and how to fix them
Cosmos (Cosmos bipinnatus) is generally forgiving once you match its basics, but a few issues come up again and again. Here is what each one looks like, why it happens, and the fix.
Topples in wind
Tall stems; stake or grow against support.
All leaves, no flowers
Too rich soil or too much nitrogen.
Aphids
Rinse with water.
Self-seeds
Welcome in most gardens; deadhead if you want to control.
Powdery mildew
Late summer; improve air flow.
Prevent cosmos problems before they start
Most cosmos issues are care-mismatch, not bad luck. Dial in the basics:
Cosmos problems — FAQ
Why is my cosmos topples in wind?
Tall stems; stake or grow against support.
Why is my cosmos all leaves, no flowers?
Too rich soil or too much nitrogen.
Why is my cosmos aphids?
Rinse with water.
Why is my cosmos self-seeds?
Welcome in most gardens; deadhead if you want to control.
Why is my cosmos powdery mildew?
Late summer; improve air flow.