Troubleshooting
Tree rhododendron problems — and how to fix them
Tree rhododendron (Rhododendron arboreum) 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.
Frost damage to flower buds
Early flower buds (January–March) are vulnerable to hard frosts. Provide overhead protection with fleece or site against a south- or west-facing wall in colder gardens. Buds turn brown and fail to open after temperatures below -8°C.
Powdery mildew
White powdery coating on leaves, especially in warm, dry summers with cool nights. Improve air circulation, avoid wetting foliage in evening, and apply a sulphur-based fungicide at first signs.
Vine weevil
C-shaped white grubs eat roots of container-grown plants from late summer to spring, causing sudden wilting and plant collapse. Apply biological control nematodes (Steinernema kraussei) to moist compost in August–September.
Prevent tree rhododendron problems before they start
Most tree rhododendron issues are care-mismatch, not bad luck. Dial in the basics:
Looking for tree rhododendron in general rather than its problems? Read the full tree rhododendron care guide — light, water, soil and feeding.
Tree rhododendron problems — FAQ
Why is my tree rhododendron frost damage to flower buds?
Early flower buds (January–March) are vulnerable to hard frosts. Provide overhead protection with fleece or site against a south- or west-facing wall in colder gardens. Buds turn brown and fail to open after temperatures below -8°C.
Why is my tree rhododendron powdery mildew?
White powdery coating on leaves, especially in warm, dry summers with cool nights. Improve air circulation, avoid wetting foliage in evening, and apply a sulphur-based fungicide at first signs.
Why is my tree rhododendron vine weevil?
C-shaped white grubs eat roots of container-grown plants from late summer to spring, causing sudden wilting and plant collapse. Apply biological control nematodes (Steinernema kraussei) to moist compost in August–September.