leeks growing in a field
Updated: June 10, 2021

Planting leeks facts

  • Hardiness: Hardy (plants can withstand heavy frosts). Biennial (a plant that requires two growing seasons to complete its life-cycle) but treated as an annual.
  • Planting: Start seeds indoors for early spring transplants or later in the summer for a fall crop. Leeks are fairly hardy and can be planted several weeks prior to the last frost date. Harden-off transplants before planting them outdoors. Transplant deeply to force long, thick, blanched stems (more information below). One leek seed or transplant will yield one sheath 6-8 inches long and 1-2 inches wide. Full sun requires direct light at least 6 hours/day; prefers 8 - 10 hours/day.
  • Days to maturity: 70 - 120, depending on the cultivar.
  • Spacing: Five inches apart, either in narrow rows or equidistantly in wide rows or beds.
  • Fertilizer needs: Light to medium requirement for nutrients, either from soil organic matter or fertilizers. Side-dress in June with a balanced fertilizer. Refer to Fertilizing Vegetables for details. 
  • Approximate yield: Five or more pounds (per 10-foot row), depending on planting style.

Leeks problem

Allium leafminer

Growing and care of leeks

  • Leeks are related to onions but instead of forming a bulb, the stem continues to thicken, forming a green sheath of furled leaves.
  • “Summer leek” cultivars, are harvested in the season when planted, and “overwintering leek” cultivars are harvested in the spring of the year following planting. Summer leek types are generally smaller than overwintering types; overwintering types are generally more strongly flavored. 
  • Blanching the stems by hilling up soil around them will make your leeks more tender and mild, but isn't absolutely necessary. You can blanch the shanks at the base by transplanting the leeks into a bed of loose soil. Use a stick or dowel about 1- to 1¼-inches in diameter to make holes in the soil about 5 to 6 inches deep. Drop a transplant into each hole. Do not fill in with soil, but water gently and the soil will wash in. As they mature, pull soil up around the plants to produce a longer blanched stem.
  • Leeks are a long-season crop. Mulching is essential to keep the weeds out and the moisture in. In fall, protect the plants with a heavy blanket of straw or leaves so they can be harvested throughout the winter. Leeks left to grow in the spring will go to seed and can be the start of a self-perpetuating leek bed. Leeks left to flower may also produce bulblets at the base of the plants. These can be separated and used to propagate a new crop.
  • Water - Leeks require regular watering throughout growth for best production. Water needs are critical since rooting depth in leeks is shallow. Drought stress will decrease yield.
  • Weeds - Control weeds through regular cultivation but avoid damaging the shallow roots of your leek plants. Weed control is particularly important during the first 2 months of growth when plants are growing slowly and competing with weeds for water and nutrients. Mulching with compost, grass clippings, or shredded leaves saved from the fall, will conserve water and smother weeds.

 Harvesting

  • Dig or pull. Leeks have large root systems so digging is sometimes easier. 
  • Leek varieties vary in their maturity times. Leeks may be harvested as early as 60 days after planting (about green onion size) but generally require 100-120 days to mature. If covered with mulch, they can be dug throughout the winter.
  • Leeks are ready to eat when the stalks are 1 inch in diameter.

Storage and preservation 

  • Long-term, leeks are best overwintered in the garden and dug as necessary. Hill up the soil around the plants and cover them with a heavy layer of mulch.
  • Leeks can be stored for 7 to 10 days in a refrigerator.