Grow Guide Conditions:
Leeks are widely adapted but grow best in cool, moderate climates. They are best grown on well drained, fertile soils with good moisture retention and a pH of 6.0–7.0. Leeks have a shallow root system and require consistent soil moisture. Hilling the shanks of the leeks several times a season to blanch is a common practice. Extremely hardy, many varieties will overwinter with good mulch.
Grow Guide Seed:
Seed summer leeks in early spring, about 4–6 weeks before average last frost date, or in mid to late summer for a fall planting to overwinter. Sow seeds thickly in a flat filled with a sterile seed starting mix, ¼ inch deep, ½ inch apart. Ideal soil temperature for germination is 65-70°F. Harden off for 1–2 weeks prior to planting. Wait a good month after the last spring frost date for warm settled weather to transplant out good sized seedlings when they are 10–12 weeks old or about pencil thick. Gently tease the crowded seedlings apart and plant 6-8 inches apart in a 4–6 inch deep trench or individual dibble holes, leaving an inch or two of foliage above the soil surface. As the plants grow taller, hill up soil around the shafts to produce long, blanched shanks. Keep well watered and weeded.
Grow Guide Pests:
Practice 3–4 year crop rotations between all Alliaceae (onion family) species to control White Rot and other diseases. Cover with floating row covers in areas where onion maggot or thrips are a problem. Nearby insectary plantings can shelter beneficials to help control pests as they become troublesome.
Grow Guide Harvest:
Harvest when shanks reach about ¾ inch diameter or larger by gently pulling the shallow rooted plants out of the ground. Loosen the soil with a digging fork if necessary. Selectively harvest the larger plants, leaving the smaller ones to continue sizing up, being careful not to disturb the roots of neighboring plants. Strip browned and dirty outer leaves and trim tops and roots. Smaller leeks can be harvested late summer, while hardy varieties may be harvested throughout the winter or the following spring before they go to seed. Leeks keep well in the ground where they are growing, or can be stored in an open topped plastic bag in the refrigerator for several weeks. They can also be stored in a cold root cellar at 32-40°F.