Perhaps the noblest Allium, which is both sweeter and milder than an onion and a space saver in the garden, is the humble leek. Learn to plant, grow, care for, and harvest leeks in your own garden so that you have a generous supply for winter comfort food and summer salads!
Leeks are a member of the genus Allium, like onions, shallots, garlic, scallions, and chives. Although they may look like an overgrown green onion, they are a different species, Allium porrum, sometimes also called A. ampeloprasum. Leeks have flat leaves and don’t make a much of a bulb.
Leeks are hardy once established, and many varieties can be left in the garden even after your frost dates and harvested as needed all fall.
What most people consider the edible portion of the leek is the white or pale green main stem, which is actually not a stalk but a bundle of leaves. However, the entire plant—minus the roots—is edible. While the white and light green parts are commonly cut up and used, even the tougher green tops (called the flag) are edible and make a great addition to your stocks and soups for flavoring.
Leeks like full sun, doing best with at least 8 hours a day, if they can get it. They need deep, fertile, well-drained soil with high organic matter levels. A soil pH of 6.0-7.0 is ideal.
When to Plant Leeks
Leeks can be bought from a garden center or greenhouse as young plants or started from seed easily at home. They are cool weather tolerant and can be planted out before your last frost.
If starting from seed indoors, you’ll want to get them sown about 10-12 weeks before your last frost date.
If transplanting your own or purchased seedlings, harden them off for several days and then plant them out 3-4 weeks before your last frost, when temperatures reach 45 degrees Fahrenheit (7°C) during the day. Leek seedlings can tolerate a light frost, and can be planted out several weeks earlier than most plants.
How to Plant Leeks
Starting leeks from seed at home is inexpensive and easier than you might suspect. While prices vary widely with variety and organic certification, you can purchase 250 leek seeds for as little as a five-dollar bill.
Sow them in soil blocks or prepared trays of well-moistened seed starting mix.
Plant the seeds about ¼ inch deep.
If planting in cell trays, drop two seeds per cell and thin to one per cell if necessary once they have germinated.
Keep them moist but not soggy, and provide plenty of light once they sprout.
Once your leeks are ready to plant out, follow these steps:
Leeks like organic matter. If needed, gently work several inches of compost into the planting bed.
Leek seedlings should be planted deeply to encourage long stalks. They can be grown in two methods: trenching or hilling. Check this page from the University of Wisconsin Extension for more information on how to plant leeks.
For trenching, dig a trench 6 inches deep. Plant your leek seedlings in the bottom and water in. Don’t fill in the trench yet. You’ll do that later.
For hilling, plant your leeks as other plants, and water in. Later you can hill them like potatoes.
Mulch your leeks to keep the soil near the surface from drying out and reduce weeds.
Whether you grew them from seed or bought transplants, caring for leeks is the same and is pretty straightforward.
Leeks have shallow root systems and will need regular watering. Irrigation provided at the soil level creates fewer problems than overhead sprinkling. Drip irrigation is ideal for running under your mulch and provides water right at the roots where your leeks need it.
About an inch per week is sufficient, however, monitor the soil. If the top 2-3 inches are dry, give them a drink. Leeks planted in sandy soil will need more water.
As your leeks grow, either fill in the trench or hill the soil. 2-3 times over the beginning of the season will be sufficient. The soil around the stem will provide a blanching effect, making the white portion longer and sweeter.
Mulch around your leeks to keep weeds down and encourage healthy soil conditions.
Take it easy with the cultivator. The shallow leek roots can be easily damaged by cultivation or hoeing. Use mulch and hand pulling to keep the weeds in check.
‘Tadorna’ is a vigorous grower with dark green-blue foliage that will overwinter in mild climates.
‘King Richard’ is a large leek with shanks that may reach a foot long. It will tolerate fall temperatures down to 20 degrees with minor damage. An early-maturing leek at 75 days, it is an excellent choice for northern gardeners.
‘Dawn Giant’ lives up to its name, with a 15-inch shank reaching 2 inches in diameter.
Leeks will be perfectly happy to sit in your garden and do their thing. Unlike some other crops, which must be harvested all at once and stored, you can go snag half a dozen leeks whenever you need them from late summer until the ground freezes.
If you live in warmer climates, usually USDA zone 7 or above, you can likely keep them in the ground all winter. As long as the ground doesn’t freeze, store your leeks in their garden bed.
Leeks can be harvested early—a great way to thin them—or left to grow larger than an inch in diameter.
Young leeks harvested at finger size will be more mild and tender and are great for eating fresh in salads or pestos. Larger leeks develop more flavor and texture.
The tops won’t die back like an onion, and in fact, in more temperate areas, leeks will display their biennial nature and bloom the second year like a carrot.
Wit and Wisdom
Leeks have been cultivated for several thousand years, probably because they are tasty!
Leeks are a national emblem of Wales. They are a symbol of the Welsh people, going back hundreds of years. The cap badge of the Welsh Guards features a leek, complete with roots.
William Shakespeare’s “Henry V” refers to wearing leeks as an ancient identification.