PLANT NOTES - VEGETABLES

Leek

Family: Alliaceae    Genus and Species: Allium ampeloprasum var. porrum

Leeks are a cool season crop, that are easy to grow in rich soil. They are a hardy biennial, grown as an annual. Leeks are related to garlic, and to onions, shallots and scallions. They grow best in partial shade in moist soil that is about 60°F. Leeks take 80 to 120 days to reach maturity depending on variety, yet can be harvested before mature. Most leeks will overwinter with mulching in our mild temperatures. A good frost will help sweeten the flavor of leeks. Blanching leeks increases the white (more tender) proportion of plant and is supposed to make for a sweeter flavor. Leek seeds store for 3 years under good conditions.

Wild leeks were used as food during the early Bronze Age around 4000 B.C. Leeks have been cultivated for more than 4,000 years.  They were part of the diet of those who built the Egyptian pyramids. Leeks have been cultivated in Western Europe since the Middle Ages and are sometimes called "the gourmet's onion" or “poor man’s asparagus” by European chefs.

Planting
Plant leeks in early fall for a winter crop. Leek seeds can be sown directly into the garden in September for a winter crop or seedling starters can be planted as soon as the intense hot September temperatures drop. Seeds or seedling starters can be planted from January to April for Spring/Summer crops. Sow about 6 leek seeds per foot ¼"-½" deep. Leek seeds germinate at 50-85° in 7-14 days. Thin to 6" apart. Leek seeds can also be sown indoors for planting as seedlings. Plant 4-6 week old seedlings in beds about 6” apart and in a zigzag pattern to utilize space or in a trench 6-8” apart in rows about 16” apart. Make sure the soil is moist and handle the seedlings gently during transplanting, making sure that they do not dry out. Some gardeners cut back the roots to 1” long and trim the tips of the leaves back slightly when transplanting.

The lower part of stem must be blanched (covered) to grow a white leek. This can be accomplished by hilling the soil up around the stalk as it develops. One way to do this is to plant in a 6-8“deep trench and then gradually fill the trench up as the plant grows. Another method is to plant the young seedlings in 6” deep holes (2” wide), up to the first leaf notch (use a thick dibble, trowel, or old broom handle to make the holes). Don't fill the holes with soil or firm the soil after planting, but just water the plants in and the hole should fill up with soil on its own as the leek grows. (Only 1” of seedling need to be sticking out above the hole.)

Cultivation
Leeks are heavy feeders and need light, well-drained soil amended with compost to a depth of 12”.  Aged manure can also be added as an amendment. Leeks will need to be generously watered during the growing season. Keep the soil evenly moist. Apply mulch to the beds to help retain moisture. Leeks may also benefit from 1-2 applications of compost tea, liquid kelp (Maxicrop), or fish emulsion.

Thinning direct seeded leeks should begin as soon as possible, when the pants are not more than thin green shoots, about six weeks from sowing.  The first thinning should be light as some of the plants may die, and then thin again to 6” apart when the seedlings are stronger.

Blanching (earthing or hilling up) is a gradual process and should be done in several stages rather than all at once. Blanching consists of gradually filling in the trench or hole with soil to the bottom of the lowest leaves each time until the plants have finished growing, giving you at least 4-6” of blanched stems.  The soil used for earthing-up must be somewhat dry, as wet earth can cause rot to set in. Earth up as necessary for the longest blanch. Leaves which grow too long can be trimmed back slightly so that they do not rest on the ground. Lift roots as required.

It has been said that leeks are a true perennial, even though they are generally referred to as biennials. If left in the ground, leeks can multiply by small lateral growths that often develop little, roundish bulbs at the base of the leek stem. Nip out the flower stems and this bonus crop, of leek bulbs will grow.  These small white bulbs will form at the base of the plant, and if you harvest them in early summer you can use them as onions or shallots.

Harvesting
Leeks can be grown as long season or short season leeks.  Long season leeks can be harvested after the first frost and throughout the fall and winter while short season leeks should be harvested from late spring through the summer. Use a garden fork to gently loosen the soil around the leek and lift from the soil. Harvest leeks any time after they are about an inch or more in diameter and approximately 24” tall, but leave them in the ground until you're ready to use them in the Sacramento area.

Fresh leeks should be stored unwashed and untrimmed in the refrigerator, where they will keep fresh for several weeks. Wrapping them loosely in a plastic bag will help them to retain moisture, but the quality will not be as good as when freshly harvested. Some gardeners believe that leeks can benefit from cooling immediately after harvest in the summer. Spray or immerse vegetables in chilled water before storing. 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. Leeks can be kept for 2-3 months if they are stored at 32°F and 95-100% relative humidity.

Companions
For crop rotation, leeks follow lettuce, cabbage or peas, but it is not a good idea to plant them immediately after lifting early potatoes. This is because the soil will be too loose and disturbed and leeks do best in a rich firm soil. Because leeks are relatively slow-growing, they can be interplanted with faster maturing crops such as lettuce, spinach, peas. Avoid planting beans or other legumes nearby as the leeks can inhibit their growth.