Troubleshooting
Greater Coreopsis problems — and how to fix them
Greater Coreopsis (Coreopsis major) 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.
Powdery mildew in shaded sites
Partial shade combined with poor air movement promotes powdery mildew. Ensure adequate spacing, prune nearby shrubs to improve airflow, and avoid wetting foliage. Generally occurs late in the season.
Root rot in heavy soils
Heavy clay or consistently wet soils cause crown rot, particularly over wet winters. Improve drainage with grit, or site on a gentle slope. This species is not suited to rain gardens.
Short bloom period
Flowers primarily in early to mid-summer and does not reliably rebloom. Deadhead spent flowers promptly and cut back stems by a third after flowering to encourage a limited second flush.
Prevent greater coreopsis problems before they start
Most greater coreopsis issues are care-mismatch, not bad luck. Dial in the basics:
Looking for greater coreopsis in general rather than its problems? Read the full greater coreopsis care guide — light, water, soil and feeding.
Greater Coreopsis problems — FAQ
Why is my greater coreopsis powdery mildew in shaded sites?
Partial shade combined with poor air movement promotes powdery mildew. Ensure adequate spacing, prune nearby shrubs to improve airflow, and avoid wetting foliage. Generally occurs late in the season.
Why is my greater coreopsis root rot in heavy soils?
Heavy clay or consistently wet soils cause crown rot, particularly over wet winters. Improve drainage with grit, or site on a gentle slope. This species is not suited to rain gardens.
Why is my greater coreopsis short bloom period?
Flowers primarily in early to mid-summer and does not reliably rebloom. Deadhead spent flowers promptly and cut back stems by a third after flowering to encourage a limited second flush.