Common Dahlia Problems (and How to Fix Them)

Powdery mildew

This fungal disease appears as a grey-white coating on leaves, typically later in the summer when nights are cool and mornings are damp. It rarely kills a plant outright, but it weakens growth and shortens vase life. To help:

Space plants so air circulates freely, and stripping off the lower leaves of the plants (knee level to ground) in midsummer can help improve airflow.

Remove and bin affected leaves.

A spray of milk diluted with water (about 1:10) can slow it down organically.

Aphids

These tiny green or black sap-suckers cluster on fresh growth and buds. They can spread quickly in warm weather. To manage:

Wash them off with a firm spray of water.

Encourage beneficial insects like ladybirds.

Snails & slugs

Young dahlia shoots are irresistible to snails. Protect your plants early:

Hand-pick them off each evening if you only have a few plants.

Use beer traps or iron-based snail pellets if needed.

Keep beds tidy and free of hiding spots.

Earwigs

These night feeders can chew petals and leaves. Rolled-up newspaper or cardboard tubes left out overnight make good traps — shake them into a bucket in the morning.

Stronger plants

The strongest defence is a thriving plant. Keep dahlias well-fed with compost or liquid seaweed, pinch off the buds for strong branching, and harvest the flowers regularly. Healthy plants bounce back faster from any setback.