Allium ampeloprasum, Porrum Group is a member of the Amaryllidaceae (amaryllis) family.
An onion like plant related to onions, chives, and garlic. Instead of forming a large bulb like an onion, leeks develop broad, succulent stems about one inch thick and six to eight inches long from roots to neck when mature; above the neck is a fan-like sheaf of flat, blue-green or yellow-green leaves that may grow another foot or two long. Types vary also in the length and thickness of their leaf shanks (a pseudo-stem).
Marketing.Baby leeks are a popular item. Different size leeks get different prices. Top ice is highly desirable to get the best market.
Wholesale market prices were reported for the Los Angeles market for leeks as follows (dry, one dozen):
Los Angeles, 1988
January-mid Feb. $9.00-12.00
mid Feb.-June $5.50-8.00
July-mid August $7.00-10.50
mid August-Dec. $8.00-12.00
Current production and yield. California, New Jersey, Michigan, and Virginia are traditional growing areas in the United States. Peak availability is in September, November, and in the spring but it is available year-round. Most of the worlds production is in Europe.
In California, in 1987, the County Agricultural Commissioners reported leeks grown commercially in Fresno, Humboldt, Monterey, Santa Barbara, Santa Clara, San Bernardino, and Ventura counties. San Bernardino County was the only one reporting actual figures. It reported a total production of 450 tons on 30 acres with a total value of $117,000. The yield was 15 tons/acre with a price of $260/ton.
In 1988 in California there were reported to be 62 harvested acres of leeks with a value of $292,000. Between 1980 and 1988 reported leek acreage has ranged from a low of 30 acres in 1987 to a high of 125 acres in 1981.
Use. The thick white leaf bases and slightly developed bulb are eaten as a cooked vegetable, in soups, or raw with or without attached leaves. The flavor is mild, sweet, delicate, and distinct from the other onion family members. The green leaves may be eaten and have a pungent odor and acrid taste. The leaves are used more for flavoring in salads and cooked dishes.
Nutrition. Leeks, like all alliums, are a good source of vitamins and minerals, especially vitamins C, B1, B2 and B6. A 3.5 ounce portion provides about 30 percent of the RDA for vitamin C. They are also a good source of potassium. Excessively high amounts of nitrogen fertilizer can cause high nitrate levels on the edible leaf and shank portions.
Climatic requirements.Leeks can withstand a considerable amount of exposure to temperatures below 32° F. They grow best in cool to moderate climates. Bolting (flowering) will occur the spring following planting. Thus, fall plantings should be avoided.
Propagation and care. Leek may be raised either by direct seeding or transplanting. From the time of seeding, the plants may occupy the land for 8 to 15 months. Thus for many growers, transplanting is preferable.
The fertilization program should be adjusted for the area, soil type, previous crop, etc. Since the crop is shallow rooted, a very sandy soil may not be suitable from a nutrient/soil moisture standpoint, even though a lighter soil would greatly assist harvesting and cleaning of the crop.
Spacing will influence individual plant sizes. The current trend in marketing is for long thin shanks (one inch in diameter) without noticeable bulbing, and as much white as possible. Wide spacing produces thick, short shanks. These may be good for the precessing crop but are less favored for fresh market.
In planning any plantings, remember that bolting (in late spring and early summer) results from exposure of plants in the field to low temperatures. This will limit summer production, since early fall plantings will bolt and spring plantings will be too small to yield well by late spring or summer.
Planting the nursery for transplant production: Seed is sown, 2 rows to a bed, on beds spaced 36-40 inches apart. The rows are 12-14 inches apart on the bed. The seed is planted about 1/2 inch deep using planters varying from a Planet Jr.® to Stanhay's®. No fertilizer is used in the nursery beds. Seed is planted at the rate of 1 to 2 pounds per acre, depending on seed size, which can be quite variable.
Nursery beds are planted from October to April, but February to April is the best planting time for the San Joaquin area. In May or June, when the plants are usually about 8 inches above ground, they are dug for transplanting. The roots and tops are trimmed so that the transplants are about 5 to 6 inches long.
Transplanted Crop: In May or June, the transplants are set into beds similar to those used for the nursery. A preplant broadcast application of 1000 pounds of a 12-12-12 fertilizer is worked in. A shank is pulled down either side of the bed to make a narrow slot into which the plants are hand planted at 4 to 6 inch spacings. Following, soil is thrown towards the plants by running a small double duckfoot shovel down the center of the bed and/or shovels alongside the bed shoulders to move soil in towards the plants. Strawberry equipment should work very well in firming in the transplants. Irrigation is then applied as soon as planting is done. Several times during the growing season, side dress fertilizer is applied, either as anhydrous ammonia in the irrigation (furrow) water or a dry fertilizer to supply an additional 100 pounds of nitrogen.
Direct Seeding: Transplants might have the advantage of producing a longer white shank because they can set deeper into the soil. However, throwing the soil up against the plant every so often can help to blanch and produce longer shanks. Direct seeding is less expensive, and determining whether or not to direct seed or transplant will depend on what a grower wants to invest in producing the crop. Transplanting helps to minimize weed control problems.
The crop shouldn't be stressed for moisture, nor over irrigated. Furrow irrigation is probably the most widely used application method, although sprinkler irrigation could be used. The method of irrigation appears to be a matter of grower preference.
Harvest and postharvest practices. A leek crop seeded in March and transplanted in mid-June can be harvested as early as November, although the plants will be less than full size at this time. The market demand for leeks is usually greatest in the winter and spring, and the bulk of the crop is harvested during this period. Plants that have reached a large size are more susceptible to bolting and will do so in the late spring or early summer. Between June and October, there is no harvest.
Plants to be harvested are undercut with a blade attached to a tractor. The blade cuts about 1 to 2 inches beneath the base of the plant. Uniform undercutting without crop injury is facilitated if the plants were set uniformly when transplanted. The large and massive root system of the leek plant at time of harvest, coupled with the fresh market demand that one inch of clean roots be left on the plant, makes the harvesting procedure difficult. After undercutting, each plant is lifted out and detached from the surface layer of soil by cutting around it with a knife. The soil at the base of the plant will be held together very strongly like a mat by the very extensive shallow roots. Although some soil is shaken off in the field, the remainder will have to be washed off with a pressure stream of water. Harvest under muddy conditions is very obviously a mess.
After the soil has been removed from the roots and the bulb stripped clean by hand and washed, the plants (topped or untopped) are tied into bunches of 2 to 5 plants depending on size, and packed into cartons. Some hand stripping is needed to remove one or more sheath of soiled or old leaves. Size grading would be a market advantage, but many growers do not go to this trouble. Presently, the market prefers some trimming of the tops.
Harvesting is essentially done once a week.
USDA storage recommendations are 32°F (0°C) at 95 to 100 percent relative humidity, with an approximate storage life of 2 to 3 months. For shipping, bunch at top, center and bottom with ties.
For mature leeks: 20 pounds net weight, 4/5 bushel carton/crate with 12 bundles. There are no federal grade standards for leeks. (Information effective Jan. 1, 1989)
Pest and weed problems. Once a good canopy is developed, week control shouldn't be a problem. However, until then leek is not very competitive. The problem is worse when the crop is direct seeded. Both nursery and main crop areas should be rotated with non-alliums to guard against diseases and pests. Pink root can be a very serious disease. Thrips are also a very serious insect problem.
Leek seed is widely available.
Brewster, James and Haim Rabinowitch. Onions and Allied Crops. 1989. CRC Press, Inc. Boca Ratan, Florida.
California Agricultural Statistics Service, CDFA. Agricultural Commissioner Data. 1980 through 1988 annual reports.
Federal-State Market News Service. Los Angeles Fresh Fruit and Vegetable Wholesale Market Prices 1988.
Jones, Henry and Louis Mann. Onions and Their Allies. Interscience Publishers Inc., New York. 1963.
Kline, Roger. "Special Vegetables." Country Journal, pp 28-32, April 1987.
The Packer. 1989 Produce Availability and Merchandising Guide.
Personal communication. Bill Fujimoto, Monterey Market, Berkeley.
Stephens, James. Minor Vegetables. Univ. of Florida Cooperative Extension Bulletin SP-40. June 1988. 123 pp.
Tropical Products Transport Handbook. USDA Agric. Handbook 668. 1987.
USDA Marketing Service. "Table of Container New Weights."
Reviewed by Warren Weber, 12/18/89
Reviewed by Yvonne Savio, 12/27/89
Reviewed by Ron Voss 1/22/90
Compiled by Ron Voss, UC Extension Vegetable Specialist, and Claudia Myers, UC Small Farm Center.
Figure 1. The leaves of the leek plant are flat in contrast with the round leaves of the onion. (Photo by Hunter Johnson).
Figure 2. The Nebraska leek variety at market. (Photo from Marita Cantwell).