Garden Variety: Some tips on growing and harvesting leeks

When many crops in Kansas vegetable gardens are nearing the end of their season, leeks are just coming into their own. Gardeners and farmers who planted them last spring may begin harvest in September to early October depending on the planting and maturity dates for the variety they are growing. With careful planning, selection, and a little extra care, harvest may continue throughout the winter.

Leeks are related to onions, garlic, shallots, and other alliums and grow in a similar fashion. At the base of the plant is a bundle of leaf sheaths that look like a small white onion. The white bulb-like structure is topped by long, slender, dark green leaves. Leeks are sold with leaves intact and much of the leaves may be used in cooking along with the white base.

Cooks use leeks raw in salads or cooked as a flavoring for soups and stews, stir-fry, Turkish and Welsh cuisine, and other dishes. They are often described as having a mild onion-like flavor. Purchasing fresh, local leeks while they are in season is the best way to try them at their peak of freshness and flavor.

To add leeks to the garden next year, plan to plant them in spring. If starting from seed, plant the seeds in trays indoors a couple of months before they will be moved outdoors. Purchasing seedlings may be easier although harder to find. Consider purchasing leek plants online or by mail order if they are unavailable locally. Plant in full sun in any type of garden with well-drained fertile soil. Leeks can even be grown in tall containers.

To get the white base on leeks, the base must be completely hidden from the sun. Plant leeks six to eight inches deep and about 6 inches apart to give them room to grow. If the plants are too short to plant at that depth at the time of transplanting, dig the hole to that depth, but only fill it in enough to support the plant. As the plant gains height, the hole can be filled in to ground level.

Mulch plants after transplanting to reduce weed competition and reduce soil and moisture fluctuations. Straw or prairie hay are typically preferred in vegetable gardens, but any sort of mulch is better than leaving bare soil around the plants.

When stems are about an inch thick, mound soil and/or mulch up on the stems to create even more depth.

Harvest begins when leeks have reached the size of your liking. Harvest a few at a time and/or as the leeks needed since they will continue to grow very slowly when left in the ground. Use a spading fork or shovel to loosen the soil around the plant and lift them out of the deep soil. Trim the roots and tops, wash, and they are ready to use.

Leeks are generally considered hardy to USDA Hardiness Zone 7. Lawrence is in Zone 6, meaning it is a little colder. In a mild winter, leeks can be harvested all season. But in a very cold winter or in a period of cold weather extremes, leeks may freeze in the ground. If very cold weather is expected, harvest any remaining leeks to avoid them freezing.

Adding an extra deep layer of mulch around the plants as winter approaches can also help them to survive especially cold temperatures.

Research varieties when selecting which leeks to grow. A few varieties have a short maturity date and may be ready to harvest in the summer after a spring planting. The best varieties for fall and winter harvest will be labeled as such or are sometimes. They typically have maturity dates of 100 to 120 days after planting.

Leeks can be interplanted with other crops to save space in a vegetable garden, or incorporated into the landscape as their foliage is attractive.

— Jennifer Smith is a former horticulture extension agent for K-State Research and Extension and horticulturist for Lawrence Parks and Recreation.