How to Grow Leeks

growing leeks

The Spruce / Randi Rhoades

Leeks are relatives of onions, with a milder, more herbal flavor that sweetens as they cook. Native to Europe and Africa and best planted in the cool early spring or fall months, leeks are characterized by tough, flat, bluish-green leaves that encircle each other, forming a cylindrical base at one end and a fan of folded leaves at the other. The leaves grow opposite each other, and the plant takes on an almost flat appearance until the leaves become long and floppy.

Although often considered a root vegetable, easy-to-grow leeks do not usually form a bulb. Instead, the edible part is the bottom 6 inches or so of the cylindrical stalk that is white instead of vibrant green. After a fairly long growing period (around three months), leeks can be harvested and used as an aromatic vegetable in soups and casseroles.

Botanical Name Allium ampeloprasum
Common Name Leek
Plant Type Herbaceous perennial
Mature Size  1–3 ft. tall, 6–12 in. wide
Sun Exposure  Full sun
Soil Type  Sandy, well-drained
Soil pH  Neutral to acidic
Bloom Time  Spring
Flower Color  White
Hardiness Zones  5–10 (USDA)
Native Area  Europe, Africa

How to Plant Leeks

Leeks are shallow-rooted, so use caution when cultivating near the plants and keep the area weed-free. For gardeners with limited space, growing shallow-rooted, fast-growing salad leaves in between your leeks while waiting for them to establish is an option.

If you want a quick harvest, you can purchase already established seedlings rather than growing from seed. Plant seedlings in holes that are at least 6-9 inches apart, with just a couple of inches of growth visible on top of the soil level. The holes should be a couple of inches wide and around 6 inches deep. Once in position, the seedlings will appreciate a generous watering.

Leek Care

Light

Leeks prefer a lot of sunshine and should be planted in the sunniest spot you can find in your garden. Ideally, you'll want to ensure they get about eight hours of bright sunlight daily throughout the entirety of their growing season.

Soil

Leeks grow best in a sandy, well-drained soil mixture that boasts a slightly acidic pH level between 6.0 and 7.0, although they will tolerate more alkaline soils as well. A nutritious soil is key to a good, leafy leek harvest, so consider amending yours with organic matter or rich compost.

Water

Leeks have shallow root systems and need to be watered frequently in order to thrive. In most environments, a weekly deep watering will suffice—however, if you live in a warmer climate or have been experiencing especially hot weather, you may need to increase your cadence. Mulching will also help keep the soil cool, retain water, and prevent weeds.

Temperature and Humidity

Temperature is not of particular importance when growing leeks. You'll want to plant them in the cool early spring months, but other than that, you really don't need to worry (though they do thrive in cooler weather). Leeks are especially cold hardy, and able to withstand temperatures well below freezing. Depending on the hardiness zone you live in, you may even be able to grow leeks (as well as other cold-hardy vegetables) throughout winter.

Fertilizer

Leeks are not heavy feeders, but because they take a while to mature, nutrient-dense soil is important to the success of your harvest. A mid-season side dressing of composted manure or a high nitrogen fertilizer is beneficial.

leek seeds
The Spruce / Randi Rhoades
leek ready for harvest
The Spruce / Randi Rhoades
leek harvest
The Spruce / Randi Rhoades

Leek Varieties

  • 'American Flag': One of the tallest heirloom varietals, the American flag leek has long, narrow shafts and a mild, sweet flavor. They're a good choice to overwinter in mild climates
  • 'Early Giant': As alluded to by its name, the early giant leek has one of the shorter maturation periods, ready to harvest in around 98 days. It also boasts especially thick stems, with a mild flavor
  • 'Autumn Giant': This tall heirloom variety can reach heights over more than 30 inches, and is typically ready to harvest in 130 days.

Harvesting Leeks

Most varieties of leeks require a fairly long growing season of 120–150 days, although some modern cultivars have been bred for shorter seasons lasting about 90 days. Unlike their cousin, the onion, leeks don't die back and signal they are ready to harvest. Instead, they are ready once the base has at least a three-inch white section and feels firm and solid. Remove from the soil by twisting and pulling or digging.

How to Grow Leeks From Seed

You can start leeks from either seeds or transplants. In colder climates, seeds can be started indoors, anywhere from eight to 12 weeks before your last spring frost. Move outdoors when temperatures begin to stay above 40 degrees Fahrenheit, and harden them off slowly (for about seven days) before transplanting them to the garden.

In warmer climates, where spring and fall are your prime growing seasons, you can start your seed indoors approximately three to four weeks before your last spring frost and transplant outdoors for an early summer harvest. Alternatively, you can direct seed in late summer and harvest in winter through early spring.

When planting leeks, space your seeds at least 6 inches apart. To encourage a succulent white stem (the edible part of the plant most frequently used in cooking), leeks must be blanched. This is another way of saying they should be hidden from the sun so that part of the plant doesn't make chlorophyll and turn green. To do so, plant seeds about 6-8 inches deep in the soil and continue to mound the soil up around the leek as it continues to grow out of the ground, starting around when the stems are an inch thick.

Common Pests/Diseases

Slugs can be a big issue for leeks (they munch on the leaves), as well as other pests that bother onions, such as onion maggots, leafminers, and thrips. You can use an organic solvent, like neem oil, to get rid of most pests. However, if a true infestation occurs, your best bet is to rip up the affected crop before the pests have to chance to spread to nearby plants.

Keep an eye out for several common diseases like blight and leek rust, which forms orange pustules on the leaves. Most of these diseases occur in damp weather—to remedy, remove the affected leaves and improve air circulation. New growth should come in healthy.

Damp weather or wet soil can also lead to leaf rot, which shows up as white spots on the tips before they eventually wither and die. There is no cure, but providing good air circulation, allowing the soil to dry between waterings, and removing any plants that appear to be infected will decrease the likelihood of occurrence.