Allium ampeloprasum (Porrum group)
Last revised February 11, 2010
Leeks. Photo credit: Alex Stone, Oregon State University
Leeks, elephant (or great-headed) garlic, and kurrat are closely related. Three types of leeks can be recognized by their morphological characteristics:
The European leek which develops a short, thick pseudostem.
The Turkish leek which develops a relatively long and thin pseudostem.
The Kurrat, which does not produce a pseudostem and is grown around the Mediterranean and in the middle east for its leaves. These leaves can be harvested several times a year.
Leeks are widely adapted, reportedly grown from Cuba to Norway. They are grown most commonly from seed, but may be propagated from topsets in the flower umbel, from bulbils in the basal plate, or from bulbs formed after the plant flowers. Varieties have been developed for resistance to cold and a wide range of winter hardiness is available. Winter hardiness is strongly correlated to a short pseudostem.
VARIETIES (approximately 80-120 days).
Main fall varieties (August through October): American Flag, Jolant, Kilima, King Richard, Primor.
Late fall - winter (October through December): Derrrick, Electra, Goldina, Goliath, Kilima, Tivi, Wintereuzen.
Overwinter (spring harvest): Carina. For trial: Conqueror (moderate bulbing), Eskimo, Siberia.
SEED AND SEED TREATMENT
Leek seed numbers approximately 176,000 per pound, but leeks are not commonly direct seeded. Use treated, high quality seed for transplant production. Leek seed, like other alliums has very limited useful viability (less than 2 years) unless stored under ideal conditions.
TRANSPLANT PRODUCTION AND PLANTING
Direct field seeding is possible but not recommended due to the lack of registered herbicides and length of time needed to harvest from direct-seeded plantings (8-12 months or longer).
For transplants, plant into containers as indicated below, or 1/2 oz of seed per sq. yard in early spring in greenhouse or field beds in March. Grow for 8 to 10 weeks before transplanting.
Harden off plants for a week or two and transplant at 10-12 weeks, or when pencil thick, into rows that are 18 to 24 inches apart, with plants at 4 to 6-inch spacing within the row. Use spacings that would allow soil to be moved from between the rows toward the plants in order to adequately blanch the stems. Leek plants are sometimes planted into 3 to 4 inches deep holes made by a dibble or dibble board. This produces long white stems that are desirable in the market.
Approximate seeding, transplanting and expected harvest dates are:
|Crop||Transplant Containers or Seed Bed||Sow Seed for Transplants||Transplant to the Field||Harvest||Field Spacing inches|
|Early||in greenhouse, modular trays or. individual containers.||mid-Dec. to mid-Jan||mid-March/ early April||July/Aug.||18 x 4|
|Summer||warm frames||mid-Jan. to late Feb.||April||late July/ late Aug.||18 x 4|
|- early||cold frames||March||early-mid June||late Aug/ late Oct.||24x 6|
|- late||cold frames||late March early Apr.||mid-late June||Nov.-Dec.||24 x 6|
|- early||outdoors||1st half April||1st half July||Jan.-Feb.||23 x 6|
|- late||outdoors April||2nd half April||2nd half July||March-May||24 x 6|
|NOTE: RISK OF BOLTING|
Leeks grow best in a cool to moderate climate. The Willamette Valley and Oregon Coast are ideal. They can be grown here year round.
A well-aerated soil with both good drainage and good moisture retention capacity with a pH of 6.5 to 7 is best. Deep plowing is recommended so that a longer shaft can be developed.
For the most current advice, see Nutrient Management for Sustainable Vegetable Cropping Systems in Western Oregon, available as a free download from the OSU Extension Catalog
Even on fertile soil apply, when available, 25-35 tons of manure per acre during the fall or early winter.
The following recommendations are general. It is advisable to use a soil test for each field to be planted.
Nitrogen: 150-200 (N) lb/acre. Spread over several applications. Use higher rates on sandy soil and with later varieties.
For Nitrogen liquid fertilizer formulations having weed control properties in leeks and other alliums, see the file Nitrogen Fertilizer Solutions Providing Ancillary Weed Control in Alliums
Phosphorus: 150-250 (P2O5) lb/acre. Potassium: 100-150 (K2O) lb/acre. Sulfur: 30-50 (S) lb/acre. Boron: 1-4 (B) lb/acre.
Irrigate uniformly to maintain vigorous, uniform growth and tender stalks. A total of 12-15 inches of water may be required depending on planting date, seasonal variation and variety.
Soil type does not affect the amount of total water needed, but does dictate frequency of water application. Lighter soils need more frequent water applications, but less water applied per application.
HARVESTING AND HANDLING
Leek yields are approximately 370 cwt/acre. Leeks do not bulb or go dormant in the fall but continue to grow slowly. The time of harvest is, therefore, very flexible, depending on the time of planting, market conditions, and variety of leek planted. Small leeks can be sold starting in early August, and varieties that have frost tolerance may be harvested throughout the fall and winter months.
Machine harvest of leeks is now possible, but most leeks are lifted or dug by machine and then harvested, cleaned, and packed by hand.
Single or multiple-row harvesters can be custom built by Krier Engineering, 4774 Morrow Rd., Modesto, CA. Contact Mr. Alex Krier, 800-344-3218, for more information.
STORAGE (Quoted or modified from USDA Ag. Handbook 66 and other sources)
Store leeks at 32 F and 95 to 100 % relative humidity. Leeks, if properly handled, should keep satisfactorily for 2 to 3 months at 32 F. Storage conditions are similar to those for celery and green onions. Leeks should be cooled promptly after harvest to near 32 F by hydrocooling, crushed ice, or vacuum cooling; and they should be kept at that temperature with high relative humidity throughout storage. Yellowing and decay develop rapidly at warmer storage temperatures. High relative humidity is essential to prevent wilting. Moderate wilting will be noted when leeks lose about 15 % of their weight after harvest. The use of polyethylene-film crate liners and of crushed ice can aid in preventing moisture loss. In one series of tests, freshly harvested and trimmed leeks prepackaged in sealed, non perforated polyethylene bags held up well for 10 weeks at 32 F under crushed ice. No off-odors, off-flavors, or tissue injury from carbon dioxide build-up or oxygen depletion were found in leeks in the sealed packages.
Good refrigeration will retard the elongation and curvature that develop in leeks at 50 F or 70 F. Respiration or heat evolution of leeks is about eight times faster at 70 F than at 32 F.
Storage for 4 to 5 months at 32 F is possible by using a controlled atmosphere (CA), although there will be some loss in quality. The best CA contains from 1 to 3 % oxygen and from 5 to 10 % carbon dioxide. This CA retards yellowing and decay. Atmospheres containing 15 to 20 % carbon dioxide cause tissue injury.
Cultivar, preharvest and postharvest conditions, degree of trimming, and method of packing will all influence the storage life of leeks.
Leeks are commonly trimmed to 12-inch length, bunched in 3`s depending on diameter, and often placed in polyethylene film bags. They are usually packaged in 10-lb cartons or wirebound crates, holding 10 film bags, each 1 lb. Other crates may be packaged with 18-24 bunches with a net weight up to 30 lb.