🧅 When to Plant Leeks

Leeks are the mildest, most cold-hardy member of the onion family, prized for a sweet, buttery flavor that only improves with cooking. Unlike bulb onions, the part you eat is the thick white and light-green shank rather than a bulb, and that shank actually sweetens after a hard frost. Because leeks take months to mature and shrug off cold better than almost anything else in the garden, they reward patient gardeners with a harvest window that can stretch from late summer into the dead of winter.

Choosing a Leek Variety

Leeks split into two broad types based on how they handle cold and how long they take to mature. Summer and fall varieties grow faster and reach harvest size earlier, but don’t hold up as well once hard freezes set in. Overwintering varieties grow more slowly and take longer to bulk up, but tolerate freezing temperatures and can stay in the ground through winter.

• Summer/fall types like King Richard mature quickly, often in around 75 to 80 days from transplant, and suit gardeners who want an earlier harvest or garden in a shorter season.
• Overwintering types like Tadorna or Bandit take longer, often 120 days or more from transplant, but their thicker shanks and cold tolerance mean you can leave them in place and pull them as needed well after other crops have finished.
• Heirloom types like American Flag, also sold as Broad London, split the difference: a long-standing variety with solid cold tolerance and a thick shank that performs reliably across zones.

If you only have room for one variety, an overwintering type gives the most flexible harvest window, since it holds well in the ground instead of needing to be pulled all at once.

Spacing, Sun, and Soil

Leeks need full sun, at least 6 hours a day, to bulk up their shanks properly. Space plants 6 inches apart within the row, with rows 12 to 18 inches apart so there’s room to hill soil as they grow.

Soil should be rich, loose, and well-drained, with a pH between 6.0 and 7.0. Work in compost or aged manure before planting, since leeks are heavy feeders that stay in the ground for months. Raised beds or deeply worked soil help too: leeks want a long, uncompacted root run rather than heavy clay to push through.

Watering Leeks

Leeks have shallow, fibrous roots and don’t tolerate drought well, so keep the soil consistently moist instead of letting it dry out between waterings. Aim for about 1 to 1.5 inches of water a week, from rain and irrigation combined, and increase that during hot, dry stretches when the shanks are actively bulking up. A layer of mulch around, but not touching, the stem helps hold moisture and keeps weeds down, which matters since young leeks compete poorly with weeds.

Top Growing Tips

• Start indoors 10-12 weeks before last frost, one of the earliest starts of any garden vegetable
• Trim seedling tops and roots back by about a third before transplanting to ease handling and reduce transplant shock
• Transplant into narrow holes 6 inches deep, drop the seedling in, and let soil fill in naturally rather than backfilling right away
• Water transplants in well and keep soil consistently moist for the first two weeks while roots establish
• Mound soil around the shank every few weeks as plants grow to blanch and lengthen the white portion
• Side-dress with compost or a balanced fertilizer partway through the season, since leeks feed heavily over their long time in the ground
• Mulch to extend the harvest into early winter; established plants tolerate light freezes without damage
• Harvest after the first frost for the sweetest, most complex flavor

Companion Planting

Good companions: carrots, celery, onions, brassicas

Carrots and leeks are a classic pairing: the leek’s scent helps mask carrots from carrot rust flies, and carrots return the favor against onion-family pests. Brassicas like cabbage and broccoli also benefit from that pest-deterrent scent, and celery shares similar watering needs, so it works well planted in an adjacent row.

Avoid planting near: legumes (beans, peas)

Alliums like leeks release compounds that can interfere with the nitrogen-fixing bacteria beans and peas rely on, so keep them in separate beds rather than side by side.

Common Leek Problems

• Bolting. A cold snap while seedlings are still young, especially several weeks below 40°F, can trigger flowering instead of shank growth. Once a leek bolts the core turns woody, and there’s no fixing it, so hold off transplanting into an extended cold stretch.
• Onion thrips. These tiny pests scar leaves with silvery streaks and thrive in hot, dry weather. Keep plants consistently watered and use row cover during peak thrips activity.
• Leek rust. Orange-red pustules on leaves, worse in humid or crowded plantings. Give plants full spacing for airflow and water at the soil line instead of overhead, especially late in the day.
• White rot. A soil-borne fungus that rots roots and shanks with no available cure once it’s established. Rotate alliums onto fresh ground every few years and avoid replanting where onions or garlic grew recently.

Harvest Timeline

Most leeks are ready 100 to 120 days after transplanting, though overwintering varieties can take longer and are worth the wait. Harvest once the shank reaches at least 1 inch in diameter, loosening the soil with a garden fork before pulling since the roots hold on tight.

Leeks don’t need to come out all at once. Because they tolerate cold so well, mature plants can stay in the ground and be pulled as needed, even after several hard frosts, which actually sweetens the flavor. In milder zones that harvest window can stretch from late summer through winter and into early spring, right up until the plants eventually bolt.