Growing Leeks

growing leeks in the garden

image source: iStock.com

ripe leek with white lower stem

Ideally, leek stems will be long and white at harvest time. The white part is where the stem was blanched underground, hidden from sunlight.

Grace your dinner table with an easy-to-grow, elegant onion cousin: the leek. Sweet and mild, leeks are gentle on the digestive system and play the role of onion in dishes, only toned down. Unlike onions, leeks don’t produce bulbs, but stash their flavor in thick, juicy stems that look similar to giant scallions. Leafy stems are pretty, and growing leeks doesn’t require much room in the garden.

In the supermarket, leeks cost a premium; harvested from the garden, they’re a bargain. Leeks are most famous for leek and potato soup, but they’re also good steamed like asparagus, oven-roasted, chopped in quiche, or wrapped in ham and baked (perhaps with a little cheese on top).

Frost-tolerant leeks thrive in cool weather. In zones 7 and warmer, plants can overwinter in the ground, making them perfect for fall planting. In northerly zones, tuck plants into beds in early spring, as soon as soil can be worked.

Soil, Planting, and Care

Separate the leek seedlings to plant each individually in the garden.

Remove leek seedlings from their Bonnie pot and gently coax them apart, then plant separately.

Plant leeks in a sunny spot in soil that is fertile and well-drained. Leeks thrive in traditional garden beds, raised beds, or even in tall containers, so choose whatever works best for you. Space leeks 6 inches apart when planting.

Leeks need two things to thrive: lots of nitrogen and consistent soil moisture. If possible, add compost or organic fertilizer to the leek bed the season prior to planting. Otherwise, work make a point to work organic matter into the ground a few days before planting.

To produce a succulent white stem, leeks must be blanched — in other words, covered or hidden from the sun. To do this, plant leeks into deep holes. (Deeper planting yields a more drought-resistant plant, too.) Create a narrow trench 6 to 8 inches deep, then tuck seedlings into the trench, adding soil back so it comes up to the base of the first green leaf. Water well.

Leek seedlings should be planted deeply up to the point where the leaves separate.

Bury the plants up to the point where the foliage arises from the stem, but not so deep that soil gets into the folds between the leaves.

After planting, mulch the bed with straw or some other organic material to help soil retain moisture. Soak newly planted leeks with a liquid fertilizer such as Bonnie Herb & Vegetable Plant Food. Water leeks as needed until plants are established. After that, plants require an inch of water a week, either through rainfall or irrigation. Inconsistent moisture yields tough stems. Continue fertilizing plants with liquid plant food every week or so during the growing season.

As leeks grow, mound the soil from the trench around stems, beginning when stems are 1 inch thick.

Troubleshooting

Leeks and kale grow in the snow in the garden. They are two of the most cold hardy vegetable plants.

Leeks are cold-hardy down to about 5 degrees. Northern gardeners often “store” their leeks in the ground through winter (snow acts as an insulator), pulling them as needed.

Soil that tumbles into leaf folds can wind up trapped between skin layers in the stem. To keep this from happening you can slip a section of paper tube, such as from toilet tissue or paper towels, over the plants while they are still young as early as planting time. The tube will rot over the growing season, but will help prevent soil from getting into leaf bases during early growth.

On young plants, slugs can be devastating. Gather them at night, set traps, or use biological control. If there is a lot of rain in winter or early spring, leaf rot can set in. Rot shows as white spots on leaf tips that eventually shrivel. At this point there is not much you can do except pull the rotted plants and thin the planting to increase air circulation.

In summer, orange pustules on leaves indicate leek rust, which is worse in wet growing seasons. Remove affected foliage; later maturing foliage will be healthy.

Because they are so cold-hardy, you could find that you still have leeks left in the garden that have made it though the winter, planted many months before. At this point, dig them because they will throw up a bloom stalk that ruins the fleshy texture of the stem.

Harvest and Storage

Leeks growing in a garden have long leaves. They are members of the onion family.

Leeks are members of the onion family with long, cold-hardy, strap-like leaves.

You can start pulling leeks from the ground just about anytime. Typically, you’d let them get least 1 inch or larger in diameter for the big white stems, but you can dig young ones to eat like scallions. If the soil is moist, they may just pull right out of the ground. If they resist, use a spading fork to loosen soil and then gently pull leeks by grabbing them at their base.

In zones 7 and warmer, you should be able to harvest leeks all winter long.

In colder areas, extend the harvest season by mulching deeply around plants (up to 1 foot deep) before a hard freeze. You could continue harvesting leeks until they are locked frozen into the ground, but don’t let that happen. Dig them first and store.

Wash the stems thoroughly to remove soil and grit that may have collected between the leaves.

For short-term storage (up to one week), tuck stems into an airtight plastic bag and place in the refrigerator crisper. For longer storage in coldest zones, dig leeks with roots attached. Cut leaves back until just an inch of green remains on each leaf. Place stems in a box (root side down) and pack with sawdust, clean sand, or vermiculite. Keep the packing moist and store in a cool place. Stems will keep up to 8 weeks.

To freeze leeks, wash, slice, and blanch for 1 minute in boiling water. Drain, drip dry, and toss into plastic freezer bags. Add the frozen leeks to soups, stews, and other dishes.

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FAQs

Should I just plant the pot of leeks like I do with other Bonnie plants?

No, this is an exception to our plant-the-pot rule. Our pots are sown thickly with leek seedlings, which means you get a lot in one pot. Gently separate the seedlings to plant.

Will leeks grow in pots?

Yes, you can grow them in containers. Use a container about 18 inches deep and fill it only about 2/3 full of soil to begin with. Continue filling as the stems grow so that they will blanch. Make sure to water and fertilize regularly. Use a liquid plant food when you water to encourage fast growth that will result in tender stems.

Just how cold hardy are leeks?

American Flag, the heirloom variety that we offer, is one of the most cold hardy. You will also run into what is called a “summer leek” which is intended to plant in spring and harvest before cold weather. However, American flag will over winter in Zones 7 and warmer, easily tolerating temperature in the teens.

If I don’t blanch my leeks are they still edible?

You can strip away the leaves and eat what white part of the stems is left below the leaves. The green portions are actually edible, but they won’t be as tender.