Troubleshooting
Double King Cup problems — and how to fix them
Double King Cup (Caltha palustris 'Multiplex') 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 on summer foliage
White powdery patches may appear on leaves in warm, dry or poorly ventilated conditions. Cut back the foliage hard immediately after spring flowering; the plant will regrow with clean leaves and the stress of summer heat is avoided as the plant is semi-dormant. Good airflow reduces recurrence.
Crown rot in excessive water depth
Planting too deeply in standing water — more than 5 cm over the crown — risks crown and rhizome rot, particularly in winter. Always position at the pond margin or on a raised basket shelf so the crown is at or just below the waterline. Lift and reposition if planted too deeply.
Clump becoming congested and flower-shy
After several years, dense clumps become congested and flowering decreases. Lift and divide every 3–4 years in late summer or early spring, discarding the old woody central portions and replanting vigorous outer sections into refreshed aquatic compost.
Prevent double king cup problems before they start
Most double king cup issues are care-mismatch, not bad luck. Dial in the basics:
Double King Cup problems — FAQ
Why is my double king cup powdery mildew on summer foliage?
White powdery patches may appear on leaves in warm, dry or poorly ventilated conditions. Cut back the foliage hard immediately after spring flowering; the plant will regrow with clean leaves and the stress of summer heat is avoided as the plant is semi-dormant. Good airflow reduces recurrence.
Why is my double king cup crown rot in excessive water depth?
Planting too deeply in standing water — more than 5 cm over the crown — risks crown and rhizome rot, particularly in winter. Always position at the pond margin or on a raised basket shelf so the crown is at or just below the waterline. Lift and reposition if planted too deeply.
Why is my double king cup clump becoming congested and flower-shy?
After several years, dense clumps become congested and flowering decreases. Lift and divide every 3–4 years in late summer or early spring, discarding the old woody central portions and replanting vigorous outer sections into refreshed aquatic compost.