Troubleshooting
Coreopsis 'Mercury Rising' problems — and how to fix them
Coreopsis 'Mercury Rising' (Coreopsis 'Mercury Rising') 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.
Crown rot in wet winters
Poorly drained soils over winter are the main threat. Improve drainage or mulch lightly around (not over) the crown.
Aphids
May appear on new shoot tips. Control with a strong water spray or insecticidal soap.
Aster yellows phytoplasma
Causes distorted, yellowed or virescent flowers. Remove and destroy affected plants immediately; no cure available.
Powdery mildew
Occasional in humid, poorly ventilated spots. Treat with potassium bicarbonate and improve airflow.
Clump decline without division
Divide every 3-4 years in spring to maintain vigorous flowering and prevent central die-out.
Prevent coreopsis 'mercury rising' problems before they start
Most coreopsis 'mercury rising' issues are care-mismatch, not bad luck. Dial in the basics:
Coreopsis 'Mercury Rising' problems — FAQ
Why is my coreopsis 'mercury rising' crown rot in wet winters?
Poorly drained soils over winter are the main threat. Improve drainage or mulch lightly around (not over) the crown.
Why is my coreopsis 'mercury rising' aphids?
May appear on new shoot tips. Control with a strong water spray or insecticidal soap.
Why is my coreopsis 'mercury rising' aster yellows phytoplasma?
Causes distorted, yellowed or virescent flowers. Remove and destroy affected plants immediately; no cure available.
Why is my coreopsis 'mercury rising' powdery mildew?
Occasional in humid, poorly ventilated spots. Treat with potassium bicarbonate and improve airflow.
Why is my coreopsis 'mercury rising' clump decline without division?
Divide every 3-4 years in spring to maintain vigorous flowering and prevent central die-out.