Troubleshooting
Knotweed Begonia problems — and how to fix them
Knotweed Begonia (Begonia polygonoides) 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
Cane begonias are highly susceptible to powdery mildew, especially in warm, dry conditions with poor air movement. Ensure good circulation around the plant, avoid overhead watering, and treat early infections with a dilute potassium bicarbonate or neem-oil spray.
Legginess and bare lower stems
Without adequate light or regular pruning, cane begonias shed their lower leaves and become top-heavy and bare at the base. Pinch growing tips regularly to encourage branching, and provide bright indirect light to keep the lower stems clothed in foliage.
Spider mites in dry conditions
Low humidity and dry compost invite spider mite infestations, which appear as tiny pale stippling on the leaf surface with fine webbing under the leaves. Raise humidity, wipe leaves with a damp cloth, and treat persistent infestations with an insecticidal soap spray.
Prevent knotweed begonia problems before they start
Most knotweed begonia issues are care-mismatch, not bad luck. Dial in the basics:
Knotweed Begonia problems — FAQ
Why is my knotweed begonia powdery mildew?
Cane begonias are highly susceptible to powdery mildew, especially in warm, dry conditions with poor air movement. Ensure good circulation around the plant, avoid overhead watering, and treat early infections with a dilute potassium bicarbonate or neem-oil spray.
Why is my knotweed begonia legginess and bare lower stems?
Without adequate light or regular pruning, cane begonias shed their lower leaves and become top-heavy and bare at the base. Pinch growing tips regularly to encourage branching, and provide bright indirect light to keep the lower stems clothed in foliage.
Why is my knotweed begonia spider mites in dry conditions?
Low humidity and dry compost invite spider mite infestations, which appear as tiny pale stippling on the leaf surface with fine webbing under the leaves. Raise humidity, wipe leaves with a damp cloth, and treat persistent infestations with an insecticidal soap spray.