Why Are My Leek Leaves Turning Yellow?

Yellowing leek leaves have several possible causes, and the pattern of yellowing — which leaves are affected, where on the plant it starts, and what else is visible — usually points clearly to the diagnosis. Leeks are robust plants and modest yellowing of the oldest, outermost leaves is entirely normal. Widespread yellowing across the whole plant or progressive yellowing from tips inward on young leaves is more significant and worth investigating.

Nitrogen deficiency

The most common cause of overall yellowing in leeks is nitrogen shortage. Leeks are moderately hungry plants and need adequate nitrogen to maintain the deep blue-green colour that healthy leek leaves should have. In poor or sandy soil, or after a wet winter that has leached nitrogen from the bed, the oldest leaves yellow first and the whole plant takes on a pale yellow-green colour rather than the correct dark blue-green. A liquid feed with a balanced fertiliser (general purpose or high-nitrogen in spring) should show visible improvement within ten days. Incorporating well-rotted compost before planting significantly reduces the risk of nitrogen deficiency over the season.

Waterlogging

Leeks planted in poorly drained ground suffer root damage in waterlogged conditions, which prevents the plant from taking up nutrients even when they are present in the soil. The result — yellowing, slow growth, stunted plants — can look identical to nutrient deficiency. If yellowing is worse after wet weather and the bed drains poorly, waterlogging is likely. Improve drainage by incorporating grit and organic matter; in the short term, reduce any supplementary watering. Leeks are reasonably tolerant of short dry spells but not of standing water around roots.

Natural outer leaf ageing

The outermost, oldest leaves of a leek naturally yellow and die back over time, particularly in late autumn and through winter. This is normal senescence and is nothing to worry about. If only the oldest, outermost leaves are yellowing and the central leaves remain dark and healthy, no intervention is needed. The yellowed outer leaves can be removed when harvesting to reveal the healthy tissue beneath.

Leek rust

Leek rust (Puccinia allii) causes distinctive orange or rust-red pustules on the leaves rather than uniform yellowing. In severe rust infections, the surrounding leaf tissue around the pustules does turn yellow and eventually dies. If you see yellow areas associated with raised orange spots, rust is the cause — see the dedicated rust page. Rust does not affect the edible part of the leek; remove badly affected outer leaves and the plant is still perfectly usable.