Growing Leeks from Seed

With their mild, subtle flavor, leeks are an elegant addition to fall and winter menus. A relative of the common onion, leeks do not form bulbs but long, tender white shanks that are perfect for savory soups, stews, and side dishes. Though not difficult to raise, leeks require a rather lengthy growing season—anywhere from 75 to 145 days, depending on the variety. Furthermore, leek seedlings can be hard to find at garden centers and nurseries, forcing would-be leek growers to raise their own.

1. Sow Seeds
Starting seeds indoors in late winter, about eight weeks before your last hard frost, will provide seedlings ready for transplanting into the garden as soon as the weather is settled. I favor five- or six-inch-diameter plastic pots, which give the roots more room than a shallow flat or cell tray. If they have been used before, wash the containers with a mild bleach solution. Fill each pot with damp commercial seedstarting or potting mix. Firm the mix with your hands to eliminate air pockets. Scatter the seeds thinly about an inch apart and cover them with one-quarter inch of additional potting mixture. Water well.

Once the seedlings appear (about 10 to 14 days), move them into bright light on a windowsill or under fluorescent lights hung a few inches above the leaves. Feed the seedlings once a week with a half-strength dose of water-soluble fertilizer.

2. Tend the Seedlings
Move the containers to a cool place where temperatures are 65 to 75 degrees Fahrenheit during the day and about 55 degrees at night. Leeks germinate best at these temperatures; warmer ones will reduce germination rates. Water the seeds with a fine spraywhen the surface of the potting mix feels dry.

3. Harden Off
Leeks are very hardy plants, but nevertheless need to be exposed gradually to outdoor conditions. About a week before your last expected frost, place the seedlings in a sheltered area outdoors where they will be exposed to a few hours of direct sunshine a day, such as on a porch. Move the pots back indoors at night if it is very cold. Gradually work the seedlings up to a full day of sun before transplanting them to the garden.

4. Transplant
Well-prepared, rich soil produces the largest leeks. Work several inches of compost and a balanced fertilizer into the planting area. Use a shovel to make trenches about six inches deep and six inches wide, spaced 18 inches apart. Empty the seedlings out of their containers and gently separate the roots. It’s a good idea to cover the roots with a little soil or a damp cloth so they don’t dry out while you work. Plant the seedlings in the bottom of each trench, setting them six inches apart. Water to settle the soil around the roots.

5. Care
In a few weeks, when the leeks are established, begin filling in the trenches with soil a little at a time. The object is to cover the lower part of the stem so it will blanch and elongate, which gives you a larger area of tender white stem. The leeks will be easier to clean at harvest time if you take care not to pile soil above the point where the leaves branch out from the stem.

Leeks are heavy feeders; work in a scattering of fertilizer each time you back fill. When the trenches are full, usually by late summer, you can pile more soil or compost between the rows to blanch the stems further. Be sure to keep the leek bed well watered because drought-stressed leeks grow unevenly and are less tender.

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Check out these great seed propagation resources:  Success With Seeds, The Plant Propagator’s Bible, and Horticulture’s Smart Gardening Techniques

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