A Guide to Growing Leeks
Leeks are an ancient vegetable that was enjoyed by the Egyptians and Mesopotamians. They are also mentioned in the Bible. Originating in the Mediterranean, they were later spread throughout Europe and Britain by the conquering Romans.
Leeks are in the same family as onions (alliums) but have a milder flavor and do not form bulbs. Rather, the leaves grow tightly together at the base which is usually blanched while growing. Most people use only the white part, but the green leaves, which are tough, can be used for flavoring sauces or as part of a bouquet garni.
Prepare your garden
Leeks prefer a slightly acidic soil with a pH of 6.0 to 6.8. They will also do well in the more alkaline soils found in most vegetable gardens. If you are going to grow your leeks in a trench, you will need to dig the trench 4 to 6 inches deep. If you prefer to hill your leeks, make sure that you have soil available throughout the season to cover the plant bases as they grow.
Seeds or starts?
If you are able to find seedlings, you can plant them directly into your garden after the outdoor temperatures consistently stay above 40°F. Most gardeners prefer to grow their leeks from seed, starting them indoors 8 to 12 weeks before their last frost in northern areas or 3 to 4 weeks before the last frost in southern growing zones.
Planting your leeks
You can plant the resulting seedlings, 6 inches apart, in your pre-dug trench, just barely covering the roots and then gradually fill in the trench throughout the season as the leeks grow. This will create the white or blanched part of the vegetable that is commonly used in cooking.
If you prefer planting your leeks at ground level, place them 6 inches apart with their roots barely covered with soil. Then throughout the growing season, you can either mound soil around the bases of your plants to blanch them or when your plants are about 8 inches tall, you can lean two boards against them to create a V-shape that will shade and blanche the bases. Some people have successfully used the cardboard tubes from toilet paper rolls to blanch their leeks. Simply plant your seedlings and then lower the cardboard tube over the plant, burying it slightly in the soil for support. The leek will grow inside the tube which will block the sun from the base, blanching it.
Leeks do not like to compete against weeds so you will need to keep them well-weeded. Be careful when weeding because leeks have very shallow roots. Make sure your plants get at least 1 inch of water per week. A thick layer of organic mulch will keep the soil moist between waterings. It is recommended that you side-dress your plants with composted manure midway through the growing season.
There are two types of leeks. So-called summer leeks are harvested the same year that they are planted. Hardier varieties are left in the ground over the winter and harvested the following spring. Over-wintering leeks are larger and stronger tasting than summer leeks.
Unlike their onion cousins, leek foliage does not die back indicating that they are ready for harvest. Rather, leeks are harvested when their bases are 1” in diameter for summer leeks or 3” in diameter for spring harvested leeks. The plants can be dug up or you can simply grab the leaves, twist and then pull the entire plant from the ground.
More growing guides
© 2014 Caren White
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