Leeks are synonymous with French cooking, which might explain their inexplicable cost in the grocery store. Leeks take only a bit more care to grow than onions, though, so don’t allow their uppity reputation to intimidate you.
Leeks need the same growing conditions as onions – rich soil, consistent moisture, and full sun. In warm climates, they tolerate partial shade. They don’t store well once harvested, so harvest them only as you need them. Leave them in the ground with a few inches of straw or grass clipping mulch and dig them up right through the winter.
Large leeks are wonderful braised, roasted, or added to casseroles and soups. They have a mellow, slightly sweet flavor that is more subtle than traditional cooking onions. Small leeks can be added raw to salads as you would green onions.
Leeks are hungry plants and need a fertile, loamy soil. Spread at least three to four inches of composted manure or compost over the soil and till it to a depth of 8 inches in your garden. To maintain adequate moisture levels, opt for soaker hoses or drip irrigation instead of overhead sprinklers. Water regularly so the soil is moist two inches beneath the surface.
Leeks are grown in two different ways, depending on your purposes. If you want large, grocery-store-type leeks for cooking, your best bet is to buy transplants or start leeks yourself indoors six to eight weeks before the last expected frost. Sow the seeds half an inch deep and a quarter of an inch apart in seed-starting trays and keep the potting mix consistently moist, but not soggy. Once the leeks stand six to twelve inches tall, you can transplant them outdoors. Tease the roots apart and plant the leeks four to eight inches deep. This deep planting promotes strong root growth and eliminates blanching tasks later. Space the leeks four to six inches apart in rows twenty inches apart.
You can also sow leeks directly in the garden about four weeks before the last expected frost. Sow the seeds half an inch deep and one inch apart. Space the rows twenty inches apart. Thin the leeks to four to six inches apart when they stand a few inches tall.
As the leeks grow, mound the soil around the base of the plant. Mound only one to two inches of soil at a time. Deep mounding can cause the roots to rot. This blanching process protects the delicate roots of the plants, conserves moisture, and ensures a flavorful, white root.
Leeks suffer few disease and pest problems. Thwart onion maggots with floating row covers; thrips can usually be dispatched with a few applications of insecticidal soap or oil. Prevent fungal diseases such as purple blotch by improving drainage through soil amendments and raised beds. Keep the leaves dry and rotate crops.
Harvesting leeks is a little more difficult than harvesting onions. Don’t try to pull them from the ground, but dig them gently with a trowel or shovel instead. Store them in the refrigerator and use them within a few days.