Why Is There White Fluffy Mould on My Garlic?

If your garlic plants are yellowing and dying, and at the base of the bulb you find a white, fluffy, cottony mould dotted with tiny black specks, you are facing white rot — the most serious and dreaded disease of garlic and onions. It is worth identifying carefully and responding to firmly, because this fungus can make a piece of ground unusable for alliums for many years. Let me explain.

How to recognise white rot

White rot attacks the roots and base (basal plate) of the garlic. Above ground, the plants yellow, wilt and die back prematurely, often in patches. When you lift an affected plant, the base of the bulb and the roots are rotted and covered in a characteristic white, fluffy, cottony fungal growth, studded with tiny black spherical bodies the size of poppy seeds — these are the sclerotia, the fungus's long-lived resting structures. That combination of white fluff and black specks at the bulb base is diagnostic of white rot, distinguishing it from other rots.

Why it is so serious

The reason white rot is so feared is those sclerotia: they survive in the soil for a very long time — commonly 8 to 10 years or more — even with no alliums present, waiting to infect the next garlic or onion crop. The fungus thrives in cool, moist conditions. There is no practical cure once soil is infected, and the disease spreads on contaminated soil, tools, and infected planting stock. So a single infected planting can contaminate ground for the better part of a decade, which is why prevention and containment matter enormously.

Containing and preventing it

If you find white rot, act firmly: remove and destroy all affected plants, bulbs and the surrounding soil if practical — never compost them, and do not replant alliums in that area for many years. Clean soil off your tools and boots to avoid spreading the sclerotia to clean beds. To prevent it in the first place: always plant clean, certified disease-free seed garlic (never suspect or supermarket cloves that could introduce it), practise long allium rotation, ensure good drainage, and keep tools and stock clean. Vigilance with planting stock is the main way the disease arrives, so clean stock is your best defence.

Living with the risk

White rot is the strongest argument for never planting questionable garlic and for rotating alliums. If your soil is infected, you can still grow garlic in containers or raised beds of fresh, clean compost well away from the contaminated ground, or in a different clean area. While it is a serious disease, careful sourcing of clean stock, good rotation and prompt containment keep most gardens free of it — and keep an infection, if it occurs, from spreading across your whole plot.