University of Maryland Extension

Leeks

bed of leeks

Leeks are a member of the onion family. The edible part of the leek plant is a long cylinder of bundled leaf sheaths which is sometimes called a stem or stalk. As the leek grows in height, soil is pulled around the base of the plant, blanching the stem- making it white and tender.

Leek cultivars can be subdivided in several ways, but the most common types are “summer leeks”, intended for harvest in the season when planted, and overwintering leeks, meant to be 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. Varieties include ‘King Richard’ and ‘Tadorna Blue’.

One leek seed or transplant will yield one sheath 6-8 inches long and 1-2 inches wide. Plant 3-6 feet of row per person per family in order to have sufficient for fresh use and storage purposes.

Planting  

Leeks can be direct seeded in the garden, but because of their long growing season (70 – 120 days) are frequently planted as seedlings. If direct seeded, seeds should be spaced 3 to 4 inches apart in rows 8 to 16 inches apart.

Leeks are easy to start from seed and should be started about eight weeks prior to planting out.  They can also be found at some garden centers in six packs or flats. Prior to planting leek seedlings in the garden, they should be hardened off by placing them in a cold frame or moving them from inside to a protected outside location. Leeks are fairly hardy and can be planted several weeks prior to the last frost date. Overwintering varieties can be left in the ground during the winter (if mulched heavily) to be harvested as needed.

In order to maximize the edible part of the plant (its long white stem), leeks should be planted in a trench that is between eight to 12 inches deep.  As the plant grows, earth is pulled into the trench, creating the long blanched stem. Alternatively, a stick can be used to create a hole 1 inch in diameter and 6 inches deep. Plants are placed in the hole and watered in. As they mature, pull soil up around the plants to produce a longer blanched stem.

Cultivation

  • Fertilizer: Prior to planting, four to six inches of organic matter should be incorporated into the soil along with an all-purpose fertilizer. Leeks are light to medium feeders and should be side-dressed in late May or June with a high nitrogen fertilizer (e.g. cottonseed meal or nitrate of soda.
  • Water: Leeks require regular watering throughout growth for best production. Moisten the soil thoroughly to a depth of 18 inches every 7 days. Water needs are critical since rooting depth in leeks is shallow. Drought stress during growth 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 compete poorly with weeds. 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 but generally require 100-120 days to mature. 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.

Nutrition 

Source of Vitamins C & A, and folate.

Preparation & Use 

Choose firm, stalks without withered tops. Remove tough, green tops, slice lengthwise and rinse thoroughly to remove sandy soil they are grown in. Cut into pieces and sauté or use in recipes.

Print: (PDF) GE113 Leeks

Blog: When does a root vegetable slip through the cracks?

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