Family: Liliaceae
Genus and Species: Allium ampeloprasum

Climate

Leeks are adapted to growing in many zones. The flavor of a leek is best after a light frost.

Soil

Good soil is the key to growing leeks. Leeks need nutrient rich, well-drained soil with a pH between 6.0 and 7.0. A good crumbly loam is what leeks truly prefer. But, they will do well in almost any garden soil as long as it is well aerated and deep (12 inches or more). Leek grows best in soils that are 60°F.

Spacing

Leeks do not take up a large amount of horizontal space, but they do need deep soil to do well. Leeks should be spaced about 6" apart. Rows of leeks should be at least 2' apart. Alternatively, plant leeks in beds 3-4' wide in a zig-zag pattern. Make sure you don't make your bed wider than what you can comfortably reach across.

Direct Seeding

Sowing leek seeds directly into the garden or field is possible, but not recommended for areas with shorter growing seasons. But if you want to give it a go, sow leek seeds in early spring, roughly 6 leeks seeds per foot 1/4" to 1/2" deep. Thin to 6" apart.

Seeding For Transplants

Sow leek seeds in flats indoors in late winter. Soil temperature should be 75° for germination. When leek starts are about 2" tall, transplant them to individual pots or starting trays with individual cells. Grow the leek seedlings under lights if available.

Germination

These seeds germinate best in soils around 68°F-78°F.
Germination will take 10-14 days.

Transplanting Into the Garden

Leeks are ready to transplant 4-6 weeks after starting. Transplant leeks 1-2 weeks after the last frost. Leek seedlings should be about 7" tall. Transplant the leeks into the prepared bed. Use a dibble to make a hole about 6" deep and drop the leek seedlings in. Only 1"-2" of the seedling need be above ground. Do not firm the soil. Lightly draw soil up to the leek seedling and let irrigation or rain do the rest. Make sure the soil is moist and handle the seedlings gently during transplanting, making sure that they do not dry out.

Watering

Leeks will need to be watered during the growing season. Keep the soil evenly moist. Applying a straw mulch to the beds help retains moisture. Leeks also benefit from bi-monthly or monthly applications of an organic fertilizer like fish emulsion.

Harvesting

Leeks are mature when they are approximately 24" tall or about 3/4" - 1" in diameter.

Leeks are mature after 70-110 days from germination. Long season leeks can be harvested after the first frost and throughout the fall and winter while short season leeks should be harvested during the summer. Use a garden fork to gently loosen the soil around the leek and lift it from the soil. Leeks can be left in the ground and harvested as needed where winters stay above 10°F.

Post-Harvest Handling

Leeks benefit from cooling immediately after harvest. Clean the leeks of dirt and cool using hydro cooling. Hydro cooling is the process of spraying or immersing vegetables in chilled water.

Storage

Leeks can be kept in a refrigerator for up to a week. Only harvest what you will need as leeks can be harvested into the fall and winter. Leeks can be kept for 2-3 months if they are stored at 32°F and 95-100% relative humidity.

Leeks are very sensitive to ethylene gas so do not store leeks with vegetables and fruits that give off ethylene gas such as apples and pears.

Diseases

Smut, Downy Mildew, Pink Root and Neck Rot

Pests

Onion maggots, and Thrips

Comments

Leeks are in the onion family. Scatter planting leeks throughout a garden or field will help ward off aphids, Japanese beetles, and carrot flies.

Many gardeners like to bank soil around the leeks as they grow. This is called blanching and it increases the amount of the stem that is whitened resulting in a sweeter stem. Do not cover up more than 3-4 inches of the lower stem of the plant.

A good frost will help sweeten the flavor of leeks.

References

Bradley, F. M. and Ellis, B. W.(Ed.). (1992), Rodale's All-New Encyclopedia of Organic Gardening: The Indispensable Resource for Every Gardener, Emmaus, Pennsylvania: Rodale Press.

Johnny's Selected Seeds (2002), "Leeks", Johnny's Selected Seeds.

Oregon State University, "Leeks, Commercial Vegetable Production Guide", Last modified 2002-12-26, Oregon State University, http://www.oregonstate.edu/Dept/NWREC/leek.html [1], Accessed 2003-05-11.

Smith, E.C. (2000), The vegetable gardener's bible: discover Ed's high yield W-O-R-D system for all North American gardening regions., Storey Books: Pownal, VT.