Key Facts
- Cool season vegetable in the onion family
- Grown for thickened leaf sheaths rather than a true bulb
- Usually grown as an annual or overwintered in mild climates
- Prefer fertile soil rich in organic matter
- Tolerant of light frost and brief freezes
- Propagated mainly by seed and transplanting
- Allium species can be toxic to dogs and cats if eaten
Leeks are a cool season allium grown for long edible leaf sheaths rather than a true bulb, prized in kitchen gardens for their mild onion flavor. They perform best in fertile, well drained soil in full sun to partial shade and tolerate light frost, but keep pets away because Allium species are toxic to dogs and cats.
Identification
Leeks produce upright, straplike leaves and a thickened white to pale green leaf sheath used for cooking. Vegetative plants grown for harvest typically reach about 12 to 24 inches tall with a spread of 4 to 6 inches when spaced for production. If left to overwinter and bolt they produce taller flowering scapes and umbrella like umbels.
Best sites and uses
Plant leeks in a sunny to partly shaded vegetable bed with fertile, well drained loam enriched with organic matter and a soil pH near 6.0 to 7.0. They work well in vegetable rows, kitchen borders and cold frame beds. In mild climates leeks can be overwintered for late winter or early spring harvests.
Planting time and spacing
Leeks are a cool season crop usually started from seed and transplanted or sown direct in cool weather. Space plants about 4 to 6 inches apart in rows to allow the long sheaths to develop and to reduce crowding that lowers quality. Planting timing varies by local climate and whether you plan to overwinter plants.
Watering and soil
Keep soil consistently moist to encourage steady root and sheath development; uneven moisture reduces quality. Leeks prefer richly amended, well drained soils because waterlogged conditions cause root rot and poor root development. Heavy soils can be used if well drained and improved with compost.
After flowering and propagation
Leeks are usually harvested before they flower, but plants allowed to overwinter may bolt and flower in midsummer. Flower heads can produce bulbils on umbels that occasionally are used for propagation, though seed and transplants are the primary methods for home and commercial production. Remove flowering scapes if you want to focus on edible harvests.
Toxicity and control
Leeks are edible for people but all Allium species can be toxic to dogs and cats if ingested and can cause red blood cell damage. Keep pets away from harvesting areas and compost that contains large amounts of Allium material. Leeks do not tend to naturalize aggressively; control spread by removing bulbils and preventing volunteer seedlings.
Frequently asked questions
- How fast does Leeks grow?
- Growth rate varies with season, variety and planting method. As a cool season vegetable leeks are usually grown to harvest size within a single growing season, with timing dependent on when seeds are sown or transplants set and local climate.
- What spacing do leeks need?
- Space leeks about 4 to 6 inches apart in rows. This common spacing supports development of the long edible sheaths and reduces competition for nutrients and moisture.
- How cold hardy are leeks?
- Leeks are generally hardy in USDA zones 3 to 9 and tolerate light frost and brief freezes. In colder regions use season extension for overwintering and in warmer zones leeks may be grown year round or treated as biennials.
- Are leeks safe for pets?
- No. Leeks and other Allium species are toxic to dogs and cats if eaten and can cause hemolytic anemia. Keep pets away from harvested leeks and large amounts of Allium in compost.
- How are leeks propagated?
- Leeks are mainly grown from seed started indoors or sown direct and often transplanted for best results. Bulbils on flower heads or division occur occasionally but are not primary propagation methods for most growers.
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