Like onions and garlic, leeks are a member of the Amaryllidaceae family. Unlike their relatives, leeks store much of their flavor in their stems instead of their bulbs, so the whole plant can be used when cooking. Leeks hail from the Mediterranean and prefer to be planted in the early spring so they can mature in moderate heat and be harvested in the summer. They are, however, relatively hardy and can withstand being outdoors year-round in most climate zones if covered.
The American Flag leek is an heirloom variety with blue-green leaves and thick white stems. A later maturing type, it does well when planted for a fall or winter harvest and can be overwintered in milder climates. Often, the stems are blanched to keep them white by mounding dirt or mulch around the base of plants.
Seed Depth: 1/4″
Space Between Plants: 6–12″
Space Between Rows: 12–18″
Germination Soil Temperature: 60–80°F
Days for Germination: 5–12
Sow Indoors: 6 to 8 weeks before average last frost.
Sow Outdoors: Transplant outdoors 2 to 3 weeks before average last frost.
Can sustain temperatures as low as 5°F but thrives in temperatures between 60–65°F. If you live in Zone 7 or above, you should be able to let your leeks overwinter and pull them as needed. In Zone 7 and below, cover your crops with straw, grass, or cloth to protect them from extreme frosts.
Natural: Full sun but will tolerate partial shade.
ARTIFICIAL: As these plants do not require extreme heat, fluorescent bulbs should suffice in helping your seedlings grow. While they don’t care for too much heat, leeks love light, so keep your light source on your baby plants for at least 16 hours a day. Be sure to keep bulbs at least 6″ from the tops of your plants to prevent burning.
Soil: Will grow in most types of soil but prefers a loamy well-drained soil for optimal growth. A pH of 6.0 to 7.5 will keep plants healthy and nourished.
Soilless: Seeds will germinate easily in most soilless mixes. A mix of perlite, well-rotted manure, and compost will help seedlings reach optimal growth.
Hydroponics: Will thrive in a hydroponic system, especially in an NFT or deep-flow system.
Aeroponics: Will thrive in an aeroponic system.
Water: Requires moderate levels of water. Although leeks are relatively drought-resistant, they do prefer even, consistent watering, so make sure soil is kept moist but not saturated. Aim for approximately 1″ of water per week.
Nutrients: A moderate feeder, leeks don’t require extensive fertilizing but do prefer nitrogen-rich soil, particularly in the earlier stages of growth. Adding a nitrogen rich compost or balanced fertilizer mix will help plants thrive.
Pruning: While pruning is not required, leeks tend to grow quite close to one another, so thin your garden as the plants begin to mature to about 6″.
Mulching: Adding a straw or wood mulch around your plants in the late fall or early winter will help keep plants alive throughout the cooler seasons. Mound mulch up around the stem but allow the green stalks to stay exposed.
Rotation: Avoid rotating leeks with other members of the allium family.
Companions: Grows well with onions, garlic, beets, bush beans, parsley, tomatoes, carrots, and celery. Avoid planting with legumes.
Harvest: Can be harvested throughout the duration of the growth period but will generally start to develop good flavor when the stems have reached approximately 1″ in diameter and tops are 8–12″ tall. To harvest, pull out of the ground by their leafy green tops. If soil is too dry, dig around the base of the plant to remove. Leeks can be harvested after the first few frosts.
Storage: Will keep for up to a week in the refrigerator. To store in this way, place the leafy greens in a plastic bag for prolonged freshness. If you would like to keep your leeks longer, trim off the majority of the leaves and place root down in a soilless mix. If living in Zone 7 or higher, keeping leeks outdoors in the ground and covered is preferable.
History: This heirloom leek variety originated around 1870 and is also known as Giant Musselburh or Scotch Flag.
Preserve: Can be frozen by first stripping the tougher outer layers and washing the plant of dirt. Cut leeks thinly and place into freezer bags. Leeks can also be dried by placing in the oven around 200°F for a few hours or until just before they have begun to crisp. When ready to use, soak in warm water until they have plumped.
Prepare: To cook, peel off the outer layers and cut off any parts of the greens that have browned or feel tough. Cut either lengthwise or into disks and rinse. Can be eaten raw, cooked in a pan, baked, or pureed in soups.
Nutritional: Contains high levels of vitamin(s) K, A, and moderate levels of vitamin(s) C, B6, and folates.
Medicinal: Has been cited as having similar medicinal properties to garlic and can promote heart health. Leeks also contain the compound allicin which is antiviral, antibacterial, and antifungal, which can assist in boosting the immune system and reducing the risk of colorectal and stomach cancer. Certain traditional medicinal practices have also cited leeks as an effective method for treating stomach parasites.
Make this simple, tasty Baked Sweet Potato and Leek dish for a filling side dish.
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