Leeks are grown for their thick, juicy stems. They are a mild-flavored alternative to the onion.
Leeks require a long growing season—up to 170 days. They grow best in cool, mild weather.
There are two types of leeks: short-season and long-season.
- Long-season leeks have thick, cylindrical stems. They take about 170 days to reach harvest. Long-season leeks are harvested late summer through the winter.
- Short-season leeks have thin stems. They mature in about 120 days. Short-season leeks are harvested during the summer. They are less hardy than long-season leeks. Short-season leeks do not store as well as long-season leeks.
Where to Plant Leeks
- Grow leeks in full sun. Leeks will tolerate partial shade.
- Leeks grow best in well-drained soil rich in organic matter. Add a couple of inches of aged compost or commercial organic planting mix to the planting bed in spring ahead of planting. Turn the soil to 12 inches deep.
- A soil pH of 6.0 to 6.8 is best for leeks.
- Grow leeks where legumes have recently grown. They will benefit from nitrogen in the soil.
- Leeks are often sown or transplanted into trenches. Trench-planting is a way to blanch the stems making them more tender and flavorful.
- Prepare trenches 6 to 8 inches (15-20cm) deep and 4 to 6 inches (10-15cm) wide. Seedlings will be transplanted to the bottom of the trench. As plants grow backfill soil in around the plants until the trench is eventually filled.
- Leeks can be planted in soil level beds. Mound up surrounding soil or mulch to blanch leeks in soil-level beds.
- The stems of leeks also can be blanched by wrapping paper or plastic tubes around the stems.
Leeks Planting Time
- Leeks require 120 to 170 days to reach harvest depending on the variety.
- Leeks grow best in temperature between 55° and 75°F (13-24°C). Growth will be slowed by hot weather.
- Grow leeks from transplants started indoors or from seed sown directly in the garden.
- Sow leek seeds indoors in early spring; start seed indoors 10 to 6 weeks before the last expected spring frost.
- Transplant seedlings into the garden as early as 4 to 5 weeks before the last expected spring frost when they are about 4 inches (10cm) tall. Transplants should be in the garden no later than early summer for autumn harvest.
- To encourage stocky stem growth, keep the tops of seedlings started indoors to 4 inches (10cm) tall until they are transplanted into the garden.
- In mild winter climates, start leeks indoors or direct sow seeds in the garden 12 weeks before the first frost in autumn for harvest in autumn or late winter.
- Leeks can tolerate warm temperatures but growth will be slowed.
- Mature leeks can tolerate cold and will survive under an insulating blanket of snow.
- Plant 12 to 15 leeks per household member.
Planting and Spacing Leeks
- Sow leek seeds ½ inch (12mm) deep.
- Seeds germinate in 10 to 14 days at 70°F (21°C).
- Thin or transplant leeks to 4 to 6 inches (10-15cm) apart. Space rows 12 to 16 inches (30-40cm) apart.
- Stagger-plant leeks in double rows; this will give fanning leaves more room to grow.
- Leeks can be sown or transplanted into trenches 5 to 6 inches (12-15cm) deep. Trench planting allows for back-filling soil around the stems as they grow; this is one method of blanching the stems. (Blanched stems will be white and tender.)
- If you transplant a seedling into a trench, continuously backfill the soil to cover all but the top 1 or 2 inches (2.5-5cm) of leaves.
- Trenches are gradually filled in over the course of the growing season.
- You can also allow watering to naturally collapse the soil around plants filling in the trenches.
Container Growing Leeks:
- Leeks require hilling for the best flavor and are not well suited for growing in containers.
Companion Plants for Leeks:
- Plant leeks with carrots, celery, garlic, and onions.
Caring for Leeks
Watering and Feeding Leeks:
- Keep the soil around leeks evenly moist; water when the surface becomes just dry.
- Prepare planting beds with well-aged manure and aged compost in advance of planting.
- Feed plants with compost tea every four weeks during the growing season.
Caring for Leeks:
- To grow large, white, succulent leeks, blanch the lower part of the stem by hilling up soil or mulch around stalks to exclude the light as they develop. You can also allow trenches to simply collapse around the stems. Blanching will make the stalks longer and tender.
- Hill up around stalks to just below the leaf junction. Do not mulch higher than the leaf junction; this will help prevent soil from lodging between leaves and stem.
- Add 12 inches or more of straw above plants when the weather nears freezing. Leeks must be protected from freezing temperatures.
Leeks Pests:
- Onion thrips may attack leeks in dry weather. Hose thrips off of plants.
- Onion maggots (the larvae of a fly) can attack leek shanks and roots. Cover plants with floating row cover to prevent flies from laying eggs.
Leeks Diseases:
- Leeks have can be attacked by rust or mildew.
- Do not overhead water leaks.
- Spray-mist plants with compost tea which is an anti-fungal.
Harvest and Storing Leeks
- Leeks can be harvested as soon as they are big enough to use. Leeks can be harvested when they are shallot-size.
- Leeks will be near their mature size when stems reach 1 to 2 inches (2.5-5cm) in diameter and leaves are 12 to 18 inches (30-45cm) tall.
- To encourage full stalk growth, cut off the top half of leaves about midsummer.
- The flavor of leeks is improved after plants are hit by a light frost.
- Lift leeks as you need them through winter but complete the harvest before the ground freezes.
How to Extend the Harvest:
- Mulch spring-planted, slow-growing leeks with a thick layer of straw in late autumn for harvest through the winter.
- Sow slower-growing varieties in summer for an early spring harvest.
- Sow fast-growing varieties in winter in a plastic tunnel or cold frame for spring harvest.
Storing and Preserving Leeks:
- Keep leeks in the garden until you are ready to use them.
- Rinse between leaves and stems to remove soil and grit.
- Leeks will keep in the refrigerator for up to one week or in a cold, moist place for 2 to 3 months.
- You can keep leeks in moist sand or soil in a cool place for six to eight weeks.
Leek Varieties to Grow
- ‘American Flag’ (90-120 days): classic, home garden variety.
- ‘Giant Musselburg’ (105 days): Scottish heirloom, best winter hardy.
- ‘King Richard’ (75 days): grows to full size in summer; not winter hardy.
- ‘Lancelot’ (70 days): bolt resistant, virus tolerant.
- ‘Lincoln’ (50-100 days): early variety with long, white shanks.
About Leeks
- The leek is a hardy biennial grown as an annual. It is a mild-flavored member of the onion family.
- Leeks have thick white stalks topped with fanning, deed-green, strap-like leaves.
- Left in the garden for a second season, leeks will flower and will not be flavorful.
- Botanical name: Allium porrum
- Origin: Mediterranean, Egypt
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