Grow Flavorful Leeks with These Essential Planting Tips

Leeks are a popular and easy-to-grow vegetable often used to add a mild onion flavor to soups, casseroles, salads, and stir-fries, but they can also be eaten raw. While a leek is part of the onion family, it differs from an onion. The edible part of a leek is usually its white stalk (the white part that grows about 6 inches above the ground), although the dark green leaves add a delicious flavor when added to stock and soups. A leek doesn’t have a bulb or hollow leaves like an onion. Instead, it has encircling blue-green leaves that form the stalk at its base and branch outward at the top.

Leeks can be raised from seed or ready-grown seedlings. Keep in mind that you need to start the planting process as early as possible because leeks require a long growing season of about 120 to 150 days.

Where to Plant Leeks

Leek seeds can be sown in containers or a seedbed before being moved to their final growing place in the garden. It’s best to prepare the leek’s final planting bed several weeks before planting by choosing a sunny location that doesn’t become waterlogged in winter. The soil should be well-drained and enriched with well-composted organic matter.

Most leeks require a long growing season of about 120 to 150 days. Choose from these methods for growing leeks from seed. 

• Start leek seeds indoors. In USDA Zones 2-8, plant leek seeds indoors eight to 10 weeks before the last spring frost date, and then set the seedlings out in the garden after that date in your area when the temperature reaches 45°F. In Zones 9-11, plant leeks in the fall for a spring crop.
• Plant directly in the garden. You can also sow seed directly in the garden in rows 12–18 inches apart about three weeks before the last spring frost date, although the resulting plants may be smaller. In warmer zones, plant seeds directly in your fall garden for a spring crop.

How and When to Plant Leeks

Jumpstart your spring gardening in Zones 2-8 by starting leek seeds indoors in flats about eight to 10 weeks before the last expected frost date. After about 10 weeks from seeding, the seedlings will be the size of a pencil. Harden off the plants before transplanting them outdoors. Water them thoroughly the day before transplanting them. In Zones 9-11, plant leeks in the fall for a spring harvest.

Plant the seedlings in 6-inch deep holes, leaving only a couple of inches of the plant above the soil line. Instead of backfilling the holes with soil, fill each hole with water to settle the soil around the roots. Planting leeks in deep holes produces long white stems. 

To get even longer stems, gradually mound soil around the stems or mulch them with straw during the growing season. This process, known as blanching, makes the stems white and mild and encourages the plants to grow taller.

Leek Care Tips

Leeks are easy to grow whether you plant an early variety or a cold-tolerant variety for fall and winter harvests. However, they are a high-maintenance plant because they require transplanting and hilling for blanching. It’s also important to keep the containers free from weeds at all times and water the leeks during dry weather.

Light

Leeks grow best in full sun. Plant them where they will receive at least 6 hours of direct sunlight a day.

Soil and Water

Plant leeks in organically rich, well-drained sandy soil. In early spring, prepare the soil for planting by turning it over to 6 inches deep and working in manure and compost. Give leek plants consistent watering during the growing season to ensure the soil maintains a medium moisture level.

Temperature and Humidity

Leeks grow best between 55° F and 75°F. The plants are somewhat frost-tolerant, so the harvest can usually be delayed beyond the first couple of light frosts in most areas.

Fertilizer

After setting the plants out in the garden, apply a transplant solution of half-strength 20-20-20 or 10-10-10 fertilizer to get the plants off to a good start. Follow the product instructions.

Pruning

Leeks don’t require pruning other than to remove any dead or diseased leaves.

Harvesting

When it’s time to harvest leeks, lift them straight out of the ground when the stems are thick. It’s easiest to loosen leeks from the soil by grasping the base of each leek and rocking it back and forth until you can pull it easily. Pull baby leeks in early summer for salads, but wait to harvest them until the lower stems thicken to 1 to 1½-inch in diameter in late summer.

Pests and Problems

If you notice that your leeks have orange raised spots, they could be infected with leek rust, a disease that often emerges in damp weather. It’s best to immediately remove any affected plants with leek rust from your garden. They are also vulnerable to onion maggots and thrips.

How to Propagate Leeks

Seeds aren’t the only way to propagate leeks. If you cut the leaves from garden leeks rather than pull the entire plant from the soil, you can water the root base, and the leek will send up new growth. As with green onions, leek bases can also be pulled up and regrown in a container of water.

Types of Leeks

‘Roxton’

Allium porrum ‘Roxton’ is an early leek variety that can be harvested in early summer in many areas. This upright plant grows quickly, and its slender stalks are perfect for grilling.

‘Giant Musselburgh’

Allium ampeloprasum ‘Giant Musselburgh’ is a large, Scottish heirloom variety that is widely adaptable. This hardy performer produces 2- to 3-inch-diameter leeks with blue-gray leaves and a mild flavor. It’s good for fall and winter harvests.

‘Caratan’

Allium porrum ‘Carentan’ is a chunky French heirloom with thick blue-green leaves and white stems that can grow up to 2 inches in diameter and 8 inches long. This late-season variety is exceptionally tender and withstands cold weather.

Leek Companion Plants

Basil

Sun-loving basil and other aromatic herbs, like thyme and rosemary, repel pests and protect leeks from harmful insects while adding extra flavor to your garden. In addition, herbs with deep roots aerate the soil, making it more welcoming for leek roots.

Carrots

Carrots enjoy the same well-drained, rich, sandy soil as leeks. They break up the soil for easier access by leak roots, and the leeks repay them by providing natural protection against carrot root flies. Plant carrots before leeks, as they take longer to reach maturity.

Strawberries

Strawberry plants enjoy full sun and consistent moisture like leeks. They also attract pollinators and suppress weed growth with their dense foliage. In exchange, the odor of leeks repels many strawberry pests.