Leeks are the quiet workhorse of the winter garden: sweet, mild and versatile, standing in the ground through frosts that would finish off most vegetables, ready to dig whenever you need them. A leek and potato soup made from leeks you dug that morning is one of winter's great pleasures.
They take 90–120 days to mature and they are hardy, so they can be sown in spring and harvested from autumn right through winter. The trick is blanching — keeping the stems in the dark so they stay white, sweet and tender.
Leeks at a glance
| Growing factor | What leeks need |
|---|---|
| Sun | full sun |
| Soil pH | 6.0–7.0 |
| Days to germination | 7–14 |
| Days to maturity | 90–120 |
| Spacing | 6–8 inches |
| Water needs | moderate |
| Cold tolerance | hardy |
| Family | Amaryllidaceae |
Starting seeds
Leeks can be started indoors or sown direct, and either route works well. Indoors, sow in trays or cells and expect germination in 7–14 days; direct-sown seed goes into prepared soil once conditions are right for the crop. Starting indoors buys you a few weeks of season and gives steadier germination, while direct sowing is simpler and avoids transplant shock.
Choose the method that fits your season length: short-season gardens in Zones 3–5 gain the most from starting indoors, while Zones 8–10 can usually direct-sow with confidence. Our seed-starting calculator works out indoor sowing dates from your frost dates, and your local extension service can confirm what works in your area.
Leeks can be started indoors or sown direct, and germination takes 7–14 days. For the main crop, sow indoors in late winter to early spring in Zones 3–6, or direct-sow in spring in Zones 7–9; in Zones 10–11 sow in autumn for a winter crop, and in frost-free Zones 11–13 grow them in the cool season. Sow thinly in trays or in a nursery bed — leeks are traditionally sown thickly in a seedbed and transplanted, which is efficient and gives strong plants. Keep the seedbed moist and weed-free while the pencil-thin seedlings establish.
Transplanting and planting out
Transplant when seedlings are about as thick as a pencil. Make a hole with a dibber, drop the seedling in, and water it in — do not fill the hole with soil, just water, so the soil washes in around the roots and the stem blanches as it grows. Space plants 6–8 inches apart in rows. As the leeks grow, earth them up a little at a time, or slip a cardboard tube over each stem, to lengthen the white blanched section. The deeper the blanch, the sweeter the leek.
When you set plants out, space them 6–8 inches apart — that spacing is what the mature plant needs, and crowding is one of the commonest causes of small harvests. Our plant-spacing calculator works out how many plants fit your bed, and the square-foot garden planner can lay the bed out for you. Harden seedlings off for a week before planting out, moving them outside for longer each day, and plant on a cloudy day or in the evening so they do not wilt in their first hours outdoors.
Soil and feeding
Leeks want rich, deep, moisture-retentive soil at pH 6.0–7.0, with plenty of well-rotted compost dug in before planting. They are hungry plants, so feed with a balanced liquid fertiliser every few weeks through summer, and a nitrogen-rich feed early on pushes the leafy growth that builds a thick stem. Avoid fresh manure, which can taint the flavour. A firm, weed-free bed matters — leeks compete badly with weeds when young.
Aim for a soil pH of 6.0–7.0 — a simple soil test will tell you where you stand, and garden lime or sulfur can nudge pH up or down over a season. Feed lightly and steadily rather than in one heavy dose: too much fast nitrogen late in the season pushes leafy growth at the expense of the part you eat. Our fertiliser calculator works out amounts for your bed size, and the raised-bed soil calculator and soil-volume calculator tell you how much mix a new bed needs. A mulch layer after planting keeps the soil moist and cool and feeds the soil as it breaks down.
Watering
Water needs are moderate: keep the soil evenly moist through the growing season, watering deeply when the top inch or two dries out. Deep, infrequent watering builds deeper roots than a daily sprinkle, and it keeps the plants steady through dry spells.
Water needs are moderate, but leeks must not dry out while they are sizing up in late summer and autumn — drought gives thin, tough stems. Water deeply in dry spells and mulch between the rows to hold moisture and smother weeds. Once the cold weather arrives, growth slows and watering needs drop, but a winter leek still appreciates a drink in a dry, frost-free spell.
Water at the base of the plant, in the morning, so the leaves dry quickly and the water reaches the roots instead of evaporating off the surface. A soaker hose or drip line is ideal. Our watering calculator gives a starting point for your bed size and soil, and the watering schedule generator can build a routine around it. Mulch is your best friend here: a few inches of straw or shredded leaves cuts evaporation and keeps moisture even between waterings.
Sunlight and temperature
Leeks need full sun for the best growth, though they tolerate a little shade better than most vegetables. They are hardy and stand through hard frosts without protection — in Zones 3–5, mulch the bed in late autumn and dig leeks as needed through winter, as long as the ground is not frozen solid. In Zones 8–10 they grow through winter easily, and in frost-free Zones 11–13 they are a cool-season crop that bolts if it gets too hot.
This crop is rated hardy for cold tolerance, so plan your season around that: hardy and frost-tolerant crops can be sown and harvested around frosts, while tender crops need warm soil and frost-free nights. Our sunlight calculator can check whether your spot gets enough sun through the season, and the hardiness-zone finder will confirm your zone. If your summers run very hot, afternoon shade or a shade cloth can keep a cool-season crop productive for a few extra weeks.
Pests and diseases
Leeks are fairly trouble-free, but a few pests find them. The ones to expect are aphids, slugs and cutworms.
- Aphids — cluster on young leaves in spring. Wash them off with water; heavy infestations can be sprayed with insecticidal soap.
- Slugs — chew young seedlings and hide between the leaves. Pick them off at dusk and keep the bed clear of debris.
- Cutworms — cut young transplants at soil level overnight. Protect seedlings with cardboard collars and check the soil at the base of damaged plants.
Inspect plants weekly, especially the undersides of leaves, and act early — a small problem caught in time is a hand-picked handful of pests, while a late one can cost the crop. Row cover keeps many flying pests off young plants, and healthy, well-watered plants resist attack far better than stressed ones. If you need help identifying what you are seeing, our pest-identifier helper and plant-disease checker walk through the symptoms.
Companion plants
Leeks grow well with marigolds, basil, onions and lettuce. Onions are the classic leek companion — the two are said to protect each other from their respective flies — and lettuce fills the ground between rows while the leeks are small. Marigolds add colour and help keep soil pests down. Avoid planting leeks near beans and peas, which do not get along with the onion family.
Good companions for leeks include:
- Marigolds
- Basil
- Onions
- Lettuce
Our companion-planting finder can suggest more pairings for your bed plan. As a general rule, avoid planting members of the same family (Amaryllidaceae) in the same spot year after year — rotate beds so soil-borne problems do not build up.
Harvesting
Start lifting leeks once the stems are thick enough to use, from about 90 days after sowing, and keep digging them as needed through autumn and winter. Loosen the soil with a fork before pulling — a leek pulled from dry, hard ground snaps. For the sweetest leeks, leave the main harvest until after a few frosts. Trim the roots and the tops, wash well between the leaves where soil collects, and use the green tops for stock.
Expect the crop to be ready about 90–120 days after sowing, though weather and variety shift that window by a week or two either way. Our harvest-date calculator works out your expected harvest date from your sowing date, and the vegetable-yield estimator can estimate how much a bed should produce. Harvest in the morning when plants are cool and crisp, and use a sharp knife or secateurs rather than tearing, which damages the plant and invites disease.
Common problems and fixes
| Problem | Likely cause | Fix |
|---|---|---|
| Thin, spindly leeks | sown too late, too crowded, or underfed | Sow early, thin to 6–8 inches, and feed through summer. |
| Bolting to seed | a cold snap on young plants, or heat | Plant out after cold spells pass; mulch to keep roots cool. |
| Rust on the leaves | fungal disease in damp, crowded conditions | Space plants for airflow and water at the base. |
Thin, spindly leeks
Likely cause: sown too late, too crowded, or underfed Leeks need a long season to thicken up, so a late sowing or crowded plants stay thin. Give them space, feed them, and be patient — they do most of their thickening in late summer and autumn.
Bolting to seed
Likely cause: a cold snap on young plants, or heat Young leeks exposed to cold can bolt when warmth returns, and heat stress does the same in summer. Time planting to avoid cold snaps and keep the soil cool and moist with mulch.
Rust on the leaves
Likely cause: fungal disease in damp, crowded conditions Orange pustules on the leaves are leek rust, worse in damp, still air. Space plants 6–8 inches apart for airflow, water the soil not the leaves, and remove badly affected leaves. The stems are usually still edible.
Frequently asked questions
How do I get white stems on leeks?
Blanch them: plant deep, and earth the stems up a little at a time as they grow, or slip cardboard tubes over them. The white part is the part kept in the dark.
When do I harvest leeks?
From about 90 days after sowing, once the stems are thick enough to use. They are hardy, so you can leave them in the ground and dig as needed all winter.
Can leeks stay in the ground all winter?
Yes — they are hardy and stand through frosts. Mulch the bed in cold zones and dig them whenever the ground is workable.
Why are my leeks so thin?
Usually sown too late, planted too close, or underfed. They need a long season, 6–8 inches of space, and regular feeding through summer.
Do leeks need a lot of water?
Moderate amounts, but they must not dry out while sizing up in late summer. Deep watering in dry spells and a mulch between rows does the job.