Leeks Growing Guide
Leeks are mildly flavoured members of the onion family, characterized by their white stem bases (shanks) topped with a fountain of green leaves. They are a popular and attractive crop, usually maturing in 4-5 months in autumn and winter, but can be left in the ground for extended harvesting. Early varieties also yield sweet, tender baby leeks in summer. Leeks have a delicious, sweet onion flavour and are versatile in cooking, suitable for brazing, grilling, roasting, sautéing, steaming, and use in casseroles, soups, and stir-fries.
This guidance applies to the crop in general. Individual varieties and local conditions can differ.
Planting information
Indoors: Sow from late winter onwards on a warm windowsill or in a greenhouse at temperatures above 7°C. Fill small pots or modular trays with seed compost, water gently, then sow seeds thinly, 1cm deep. Keep seedlings warm (at least 10°C) and in good light, watering regularly. Transplant outdoors after about eight weeks when 20cm tall, after the last frost. Outdoors: Sow in March and April for main crops, or May and June for later crops/baby leeks. Prepare the ground, make a shallow drill 1cm deep, water, then sow seeds thinly, 1cm deep, in rows 20cm apart. Cover early sowings with cloche or fleece if temperatures drop. Transplant young leeks when they are about 20cm tall and pencil thick, typically after about eight weeks if grown indoors. Acclimatise indoor-grown plants by hardening off first. Prepare the soil and water plants well before transplanting. Make holes 15cm deep and 5cm across, spaced 15-20cm apart (10cm for baby leeks). Space rows 30cm apart. Trim leek roots to 2.5cm. Stand one leek in each hole, then fill holes with water to settle soil around roots ('puddling in'), no need to backfill. Can also be transplanted into large pots (up to six in a 40cm container), or 10cm apart for mini-leeks, using the same deep planting method.
Harvesting information
Leeks can be harvested at any size; baby leeks mature in a couple of months, while large ones take four months or more. Begin harvesting small plants from late summer to extend the cropping period. Lift individual plants gently with a fork. Hardy varieties can remain in the ground through winter and spring for on-demand harvesting. Before cooking, slice lengthways and wash out soil. If plants bolt, remove the flower stalk while the bud is green and tightly closed; these scapes are edible.