How to Grow Leeks

Starting and planting

Leeks grow in all soil types as long as they are rich, well-drained, moist, and fertile, and they want full sun. Because they are slow, start seed indoors 6 to 8 weeks before planting out; direct-sow around late March or set transplants in April.

Plant seeds a quarter to a half inch deep, 3 to 4 inches apart in the row, with 8 to 16 inches between rows; transplants use the same spacing. Weeds compete hardest during the first two months, so keep the young rows clean.

For the localized planting date and the in-row spacing question alone, the when-to-plant-leeks and leek-spacing calculators answer those directly.

Blanching by hilling, water, and feed

The pale, tender white shaft is the point of growing leeks, and you build it by hilling. During the season, mound soil around the plants two to three times, adding 2 to 3 inches of banked soil each time, which encourages taller growth and a longer blanched edible stem. Some growers plant into a shallow trench and fill it gradually for the same effect.

Keep the soil near field capacity — Utah State Extension moistens the soil thoroughly to a depth of 18 inches every 7 days. Consistent deep moisture is what keeps leeks fat and mild.

Side-dress nitrogen at about a quarter pound of 21-0-0 per 100 square feet in mid-May and again in late June. The how-often-to-water-leeks and best-fertilizer-for-leeks calculators cover those two inputs on their own.

Problems and harvest

The main pests are thrips, onion maggots, and wireworms. Rotating away from where onions or leeks grew last year reduces maggot pressure.

Leeks generally require 100 to 120 days to mature. Harvest once stalks are about 1 inch in diameter — there is no rush, since leeks hold in the ground and tolerate cold, so you can dig them as the kitchen needs through fall and into winter in milder areas.

Lift with a fork rather than pulling; the deep, hilled roots resist a straight tug. The when-to-harvest-leeks calculator gives the size-and-timing readout on its own.

Sources

Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.

• Utah State University Extension — Leeks in the Garden — Leeks grow in all soil types provided they are rich, well-drained, moist, and fertile, in full sun; start seed indoors 6-8 weeks before planting out, sow seeds late March or transplant in April; plant 1/4-1/2 inch deep, 3-4 inches apart in the row, 8-16 inches between rows; hill soil around plants 2-3 times adding 2-3 inches of banked soil to encourage a longer blanched white stem; maintain soil near field capacity, moistening to 18 inches deep every 7 days; side-dress 1/4 lb 21-0-0 per 100 square feet in mid-May and late June; pests include thrips, onion maggots, wireworms; weeds compete during the first 2 months; leeks require 100-120 days to mature and are harvested when stalks are 1 inch in diameter.

Keep going