How to Grow Leeks
Leeks have been used as a culinary crop for at least 4,000 years. Enjoy this historic allium in your garden and try your hand at biennial seed saving.
Time of Planting
Sow leek seeds indoors 8-10 weeks before the last frost date. Seedlings can be transplanted outside as soon as the risk of hard frost has passed.
Plant leek seeds ¼ inch deep into flats. When transplanting leeks into your garden, space them 6 inches apart.
Time to Germination
Leeks like soil rich in organic matter. They’re also a heavy feeder—meaning they prefer a high-nitrogen fertilizer.
Common Pests and Diseases
Leeks can suffer from downy mildew, white rot, and leaf blight. Take care to rotate plant families in your garden to prevent diseases.
When and How to Harvest
Harvest leeks when they reach a diameter of between ½ to 1-½ inches. Take care to thoroughly wash your leek plants before cooking with them; dirt can accumulate between their tall leaves.
Leek can be used in many recipes that call for onions. The flavor and texture of leek holds up to a lot of cooking, so use leeks in soups, stews, and other simmered dishes.
Whole leeks will store for weeks in a refrigerator and months in a root cellar.
How to Save Leek Seeds
It may take additional time and effort to cultivate leeks for seeds rather than for eating, but because this biennial crop is fairly cold hardy, it can overwinter in the garden in many regions.
Recommended Isolation Distance
Separate varieties by 800 to ½ mile in their second year of growth.
Recommended Population Sizes
To ensure viable seeds, save seeds from at least 5 plants. When maintaining a variety over many generations, save seeds from 20-50 plants. If you’re saving seeds for genetic preservation of a rare variety, save seeds from 80 plants.
To produce seed from leeks, select several perfect leeks and store them through winter. Ideally, store leeks in a cool, dry space away from sunlight. Replant leeks in early spring using the same spacing used in their first year of growth. Staking leeks to prevent lodging during flowering is recommended.
Assessing Seed Maturity
Seed maturity occurs in the second growing season, when capsules split open to expose mature black seeds.
To harvest, cut the scape about 6 to 8 inches below the seed head. The harvested umbels should be placed in an open container or bag, or on a screen, to continue drying in a well-ventilated space for at least seven days. A longer drying period can make threshing easier, especially if many fruits were still green at harvest.
Cleaning and Processing
After the plants bloom and seed heads begin to dry, gather the heads in a paper bag and shake the seeds free. Allow the seeds to air-dry for a few days before storing the seeds in a cool, dry place.
Storage and Viability
Leek seeds will remain viable in cool, dry storage for a couple of years.