How to Grow Leek

Growing guide

Overview

Leeks are cold-hardy alliums grown for their thick, mild-flavored white stalks, which you harvest from late summer right through winter. Gardeners love them because they stand in the ground for months without spoiling and actually taste sweeter after frost. They need a long season, full sun, and steady moisture to size up well.

Soil & planting prep

Leeks grow best in loose, well-drained loam or clay loam that holds moisture without staying soggy. Aim for a pH near 6.0–7.0; add compost or aged manure the fall before planting. Set transplants 6 inches apart in rows 12–18 inches apart, and plant them deep — 4–6 inches — so the stems blanch white.

When to plant

Start leek seeds indoors about 12 weeks before your last frost date — late winter for most gardeners. Transplant seedlings into the garden 2–4 weeks before the last expected frost, once they’re pencil-thick; leeks tolerate cold and even light frost. In mild-winter areas you can also sow a fall crop in late summer for winter harvest.

How to plant

1. Fill seed trays with seed-starting mix and sow seeds 1/4 inch deep, 1 inch apart, about 12 weeks before your last frost date.
2. Keep the trays at 60–70°F and moist; seedlings will germinate in 7–14 days.
3. Trim the tops to about 4 inches tall every few weeks to keep plants sturdy and encourage thick stems.
4. Harden off seedlings for 7–10 days, then transplant when they’re 6–8 inches tall and pencil-thick.
5. Make 6-inch-deep trenches or dibbled holes 6 inches apart, drop a seedling in each, and water in without backfilling completely — fill the trench gradually as the leeks grow to blanch the stems.

5 common mistakes to avoid

• Starting seeds too late — leeks need 100–150 days, so sowing in spring instead of late winter leaves you with thin, small stalks by fall.
• Planting shallow — if you set seedlings only an inch or two deep, the stems stay green and tough instead of forming the long white shank you want.
• Letting the bed dry out — leeks have shallow roots and drought stress stops growth, so water deeply once a week in dry weather.
• Skipping the gradual trench fill — if you never backfill soil around the stems, you lose the blanched white portion that makes leeks worth growing.
• Harvesting too early — pulling leeks before they reach 1–1.5 inches across gives you skinny, less flavorful stalks; wait until they size up, and leave them in the ground through light frosts for better flavor.

Harvesting & storage

Leeks are ready when the stalks are 1–1.5 inches thick and firm, usually 100–150 days from sowing. Loosen the soil with a fork and lift them carefully so you don’t break the roots, or simply pull if the ground is loose. Store unwashed leeks in a cool, humid spot (32–40°F) for weeks, or in the fridge wrapped in damp paper towels; they also hold well in the garden under mulch in mild winters.

Companion planting

Good companions for leeks include carrots, celery, and onions, which share similar growing needs. Avoid planting them with beans or peas, as alliums can stunt legumes.

Growing in containers

Leeks grow well in containers — use at least a 5-gallon pot per plant or a deep window box with 6-inch spacing. Fill with a rich potting mix and water regularly, since containers dry out faster than garden beds.

Pro tips

Start indoors in late winter — leeks need a very long season. Transplant deeply to blanch stems. Harvest after first frosts — cold improves flavour. Very cold-hardy surviving to -10°C.