Why Is My Lavender Going Grey and Mouldy?

When lavender foliage or stems develop a visible grey, fuzzy coating rather than simply turning grey and dying, the culprit is usually botrytis — grey mould caused by the fungus Botrytis cinerea. This is a different problem from shab or root rot and is identified by the fluffy, ash-grey spore masses that form on infected tissue, particularly in cool, damp conditions. Botrytis is an opportunist that attacks weakened, dead or damaged plant tissue, and lavender becomes especially vulnerable when conditions are far removed from its preferred dry, sunny habitat.

Identifying botrytis on lavender

Look for soft, brown, water-soaked patches on stems or leaves that quickly develop a coating of fine grey powder — the fungal spore masses. These release a puff of grey smoke when disturbed. Infected tissues collapse and die, and the fungus spreads to adjacent healthy tissue if conditions remain wet and cool. Botrytis is most common in autumn and early spring when nights are cold and humidity is high, and after prolonged rainy spells in summer.

Removing infected material

Cut away all visibly infected stems and foliage, taking the cut back to clearly healthy tissue. Do this on a dry day to avoid spreading wet spores across the plant. Bag and bin the removed material immediately. Avoid touching healthy parts of the plant with the same tool or gloves that contacted infected tissue. After pruning, thin the remaining growth to improve airflow through the plant.

Improving air circulation

Botrytis spores require humid, still air to germinate on plant surfaces. Lavender grown in dense, crowded beds or overhanging other plants suffers far more than those in open, airy positions. Space lavender plants at least 45 to 60 cm apart, prune annually to maintain an open structure, and avoid planting next to walls or in corners that trap damp air. A mulch of gravel or grit around the base also helps by reflecting heat and keeping the crown dry.

Reducing moisture and humidity

Do not water lavender from overhead — water splashing onto foliage promotes botrytis. If irrigation is necessary, deliver it directly to the soil at the base of the plant. Avoid misting or wetting the foliage, and do not water in the evening when temperatures are dropping and moisture evaporates slowly.

Chemical options

In severe cases, a fungicide containing myclobutanil or trifloxystrobin labelled for botrytis control can reduce spread, but chemical treatment alone without improving growing conditions simply delays recurrence. Address the underlying causes — poor drainage, high humidity, overcrowding — for lasting control.