How to grow leeks

Leek is a biennial allium grown as an annual, building a thick, cylindrical shank rather than the bulb its onion relatives produce. Mature plants stand two to three feet tall, with broad, flat leaves that arch outward in two opposing ranks and take on a distinctive blue-green cast. The shank is pale ivory at its base, turning green where light reaches it. Gardeners grow leeks for their mild, sweet flavor, which holds well through long cooking without turning sharp. The plant commands bed space for the better part of a growing season, and its slow development demands planning several months ahead.

The critical technique is progressive hilling: mounding soil or compost up along the shank several times during the season, or setting transplants into a deep furrow and gradually filling it in, to keep the lower stem in darkness. When this step is neglected, the shank develops short and almost entirely green, and green leek tissue is fibrous, strongly flavored, and unsuitable for the recipes that make the crop worth growing. A gardener who has grown onions, which need no such treatment, tends to skip hilling entirely and finishes the season with a harvest of tough, mostly inedible stems.