Troubleshooting
Chocolate Cosmos problems — and how to fix them
Chocolate Cosmos (Cosmos atrosanguineus) 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.
Tuber rot over winter
Cold, wet soil rots the dormant tuber. Lift and store dry and frost-free in cold areas, or mulch heavily and ensure perfect drainage.
Slugs and snails
Graze emerging spring shoots. Protect new growth as it appears, when the plant is most vulnerable.
Failure to reappear
Slow to break dormancy in spring; an unsprouted tuber is often dormant, not dead. Be patient and keep it barely moist, not wet.
Powdery mildew
Affects foliage in humid late summer. Improve spacing and airflow and remove infected leaves.
Prevent chocolate cosmos problems before they start
Most chocolate cosmos issues are care-mismatch, not bad luck. Dial in the basics:
Looking for chocolate cosmos in general rather than its problems? Read the full chocolate cosmos care guide — light, water, soil and feeding.
Chocolate Cosmos problems — FAQ
Why is my chocolate cosmos tuber rot over winter?
Cold, wet soil rots the dormant tuber. Lift and store dry and frost-free in cold areas, or mulch heavily and ensure perfect drainage.
Why is my chocolate cosmos slugs and snails?
Graze emerging spring shoots. Protect new growth as it appears, when the plant is most vulnerable.
Why is my chocolate cosmos failure to reappear?
Slow to break dormancy in spring; an unsprouted tuber is often dormant, not dead. Be patient and keep it barely moist, not wet.
Why is my chocolate cosmos powdery mildew?
Affects foliage in humid late summer. Improve spacing and airflow and remove infected leaves.