Leeks
Allium ampeloprasum
(Porrum group)
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 time 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 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:
Transplant Sow Seed Field
Containers for Transplant Spacing
Crop or Seed Bed Transplants to the Field Harvest inches
Early in greenhouse, mid-Dec. to mid-March/ July/Aug. 18 x 4
modular trays or mid-Jan. early April
individual con-
tainers.
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Summer warm frames mid-Jan.to April late July/ 18 x 4
late Feb. late Aug.
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Fall
- early cold frames March early-mid late Aug/ 24x 6
June late Oct.
- late cold frames late March mid-late Nov.-Dec. 24 x 6
early Apr. June
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Winter
- early outdoors 1st half 1st half Jan.-Feb. 23 x 6
April July
- late outdoors 2nd half 2nd half March-May 24 x 6
April April July NOTE: RISK OF BOLTING
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ADAPTABILITY 
Leeks grow
best in a cool to moderate climate. The Willamette Valley and Oregon Coast
are ideal. They can be grown here year round.
SOIL
A well-aerated
soil with a 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.
FERTILISATION
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. Phosphorus: 150-250 (P2O5) lb/acre.
Potassium: 100-150 (K2O) lb/acre.
Sulfur: 30-50 (S) lb/acre.
Boron: 1-4 (B) lb/acre.
IRRIGATION
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, HANDLING, AND STORAGE
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 form
USDA Ag. Handbook #66)
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.
PACKAGING
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.
INSECT CONTROL FOR LEEKS THE INSECTICIDES LISTED
BELOW, TAKEN FROM THE PACIFIC NORTHWEST INSECT CONTROL HANDBOOK, ARE FOR
INFORMATION ONLY, AND ARE REVISED ONLY ANNUALLY. BECAUSE OF CONSTANTLY CHANGING
LABELS, LAWS, AND REGULATIONS, OREGON STATE UNIVERSITY CAN ASSUME NO LIABILITY
FOR THE CONSEQUENCES OF USE OF CHEMICALS SUGGESTED HERE. IN ALL CASES, READ
AND FOLLOW THE DIRECTIONS AND PRECAUTIONARY STATEMENTS ON THE SPECIFIC PESTICIDE
PRODUCT LABEL.
USE PESTICIDES SAFELY!
Wear protective clothing
and safety devices as recommended on the label. Bathe or shower after each
use.
Read the pesticide label--even
if you've used the pesticide before. Follow closely the instructions on
the label (and any other directions you have).
Be cautious when you
apply pesticides. Know your legal responsibility as a pesticide applicator.
You may be liable for injury or damage resulting from pesticide use.
Insect and Description Control, Active Ingredient/Acre
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Onion thrips malathion - 1.25 to 1.8 lb
Thrips tabaci
Pyrellin - 1 to 2 pt
Adults are small, slender,
feather-winged insects. Mustang 1.5 EW - 0.0375
Young are wingless. Feed to 0.05 lb
on foliage and may kill tops.
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DISEASE CONTROL
The Pacific Northwest Disease Control Handbook has no control entries for
this crop. Fungicides registered on leeks, but not evaluated by University
personnel in the Pacific Northwest, include: Bravo, COC, Ridomil, and Telone.
Consult labels for rates, restrictions, and diseases controlled. Most diseases
that attack onions also may affect leeks. Proper rotations, field selection,
sanitation, spacings, fertilizer and irrigation practices can reduce the
risk of many diseases. Fields can be tested for presence of harmful nematodes.
Using seed from reputable sources reduces risk from "seedborne" diseases.
For updates on above information and authors, please click on osu.orst.edu/Dept/NWREC/vegindex.html
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