White Fluffy Mould at the Base of My Leeks

Dense white fluffy fungal growth at the base of leek stems, at or just below soil level, often with tiny black pin-head-sized bodies embedded in the white growth — this is white rot, caused by Sclerotinia cepivorum. The same disease affects all alliums: onions, garlic, chives, and shallots as well as leeks. It is one of the most serious allium diseases because its resting structures (sclerotia) persist in the soil for 20 years or more, making the affected ground permanently hostile to alliums unless managed carefully. Identifying it early and understanding what it means for your garden is essential.

How white rot spreads and survives

Sclerotinia cepivorum produces tiny, hard, black sclerotia — survival structures visible as pinhead dots in the white mycelium. These sclerotia fall into the soil and remain dormant, sometimes for two decades. They only germinate in response to chemical signals released by allium roots — garlic sulphur compounds are particularly potent triggers. This specificity means the disease builds up in soil where alliums are grown repeatedly and has no effect on non-allium crops. Spores spread slowly within a bed from an initial infection focus, which is why affected plants often appear in clusters rather than uniformly across the bed.

Immediate response

Remove all affected plants along with a generous volume of surrounding soil (a spade's width around each affected plant). Dispose of everything off-site — do not compost. Do not allow soil or tools that have touched the infected area to spread to other parts of the garden; sclerotia are easily transported on boots, spades, and wheelbarrows. Mark the affected area clearly. Growing any allium in that area again carries significant risk for the foreseeable future.

Long-term management

The only reliable management strategy is strict, long-term crop rotation. Avoid all alliums in the affected bed for as many years as possible — the longer the gap without a host, the lower the sclerotial population in the soil. Non-allium crops are completely safe to grow in the same ground. For gardeners with limited space, growing alliums in containers with fresh, bought-in compost completely avoids the soil-borne risk and allows continued leek and onion growing while the affected bed lies idle.

Were the leeks edible?

Leeks infected with white rot at the base are not suitable for eating — the basal tissue is rotten. However, if you catch a plant early when only the very base is affected, the upper shank (well above the infection) can sometimes be salvaged — cut well above any discoloured tissue and use immediately. Do not store any leek from a white rot-affected plant.