Quick answer
Sow leeks in spring, raise them in a seedbed or modules, then transplant into deep holes 15–20cm apart. Keep young plants watered and weed-free, earth soil around the stems gradually for a longer white shank and lift as needed from late summer through winter. Hardy late cultivars can stand into spring.
Leeks are slow but space-efficient early in their life. A temporary seedbed lets seedlings grow while another crop occupies their final bed. Transplanting is not just relocation: setting the plants deeply creates more blanched, tender stem.
Choose by harvest season
Early leeks mature from late summer into autumn and are often less hardy. Mid-season cultivars crop through winter. Late, very hardy leeks can stand until spring but occupy the ground longest. Baby-leek cultivars are harvested at closer spacing and do not need six months to reach full diameter.
Look for rust resistance if orange pustules have previously reduced the crop. Bolt resistance matters where young plants may experience cold. Blue-green winter cultivars are commonly selected for hardiness, while long-shanked types suit growers who want a large blanched portion.
Site, soil and rotation
Choose full sun and deep, fertile, well-drained soil around pH 6.0–7.0. Leeks tolerate heavier ground if it drains, but harvesting becomes difficult when sticky soil is saturated. Incorporate mature compost well before planting and remove perennial weeds.
Rotate away from onions, garlic, shallots and other alliums for several years where white rot, leek moth or allium leaf miner has occurred. These crops share pests and diseases. Clean soil from tools before moving from an affected bed.
Because narrow leek leaves cast little shade, weeds compete throughout the season. Prepare a clean final bed rather than expecting established plants to suppress them.
Sowing and raising seedlings
For an early crop, sow indoors in late winter into modules or pots. For a standard crop, sow in a protected outdoor seedbed in spring. Place seeds about 1.5cm deep, keep evenly moist and thin crowded seedlings.
Provide indoor seedlings with bright light and temperatures above roughly 10°C. Harden them before planting outdoors. Seedbed plants are usually ready when about pencil thickness or 20cm tall, although timing and cultivar vary.
Cold checks during the juvenile stage can trigger bolting later. Protect very early sowings from severe cold and avoid keeping mature seedlings cramped for too long.
Transplanting and blanching
Make vertical holes about 15cm deep with a dibber, spacing them 15–20cm apart and leaving roughly 30cm between rows. Set one leek in each hole and fill the hole with water to settle soil around the roots. Traditional practice leaves the hole open rather than backfilling it.
Some methods trim roots or leaves before planting, but this is not essential when module-grown plants fit the hole. Minimise damage and preserve the growing point.
As leeks grow, draw up soil gradually to exclude light and lengthen the white shank. Keep soil out of the leaf fan, where it becomes trapped. Collars made from card or pipe can blanch stems without as much earthing, but must not harbour slugs or constrict growth.
Spacing and containers
Use 15–20cm for full-size leeks and about 10cm for baby leeks. Wider spacing encourages thicker stems; closer spacing produces slimmer plants.
A deep, wide pot can hold baby leeks or several mature plants. The RHS leek guide suggests four or five mature leeks in a container about 40cm wide. Use at least 20 litres for a useful small group, with 30cm depth and free drainage. Container leeks need more frequent watering than ground crops.
Watering, feeding and crop protection
Water seedlings and transplants until established. Mature leeks in open ground then need water mainly during prolonged dry spells; containers need regular checks. Direct water to soil and mulch to reduce evaporation.
On fertile soil, a modest nitrogen application during active summer growth may be sufficient. Late heavy feeding can create soft growth. Weed shallowly and hand-weed close to stems.
Fine insect mesh installed before adult pests arrive can exclude leek moth and allium leaf miner. Seal edges and leave headroom. Remove and destroy affected tissue according to local pest guidance rather than composting live larvae.
Diagnosing common problems
| Symptom | Likely causes to investigate | First checks |
|---|---|---|
| Orange powdery spots | Leek rust | Pustules, crowding and cultivar |
| Leaves contain mines or split | Allium leaf miner or leek moth | Larvae, pupae and local pest season |
| Plant yellows and roots rot | Allium white rot or waterlogging | White fungal growth, sclerotia and drainage |
| Central flower stalk forms | Bolting after cold or plant stress | Sowing history and stalk firmness |
| Shank remains short and green | Shallow planting or little blanching | Planting depth and earthing up |
| Grit fills the stem | Soil entered the leaf fan | Earthing technique and washing method |
Harvest and storage
Harvest baby leeks once they reach a useful diameter. Lift full-size plants with a fork, loosening soil beside the roots rather than pulling and snapping the shank. Take alternate plants first to give neighbours more room.
Hardy winter leeks can remain in the ground until needed, but lift a supply before the soil freezes solid. Late plants should be cleared before they bolt in spring. Wash carefully between leaf layers.
Leeks store for a limited period in a refrigerator and are often best left standing where conditions permit. Slice, blanch and freeze surplus. Do not store plants showing active rot with sound ones.
Sources and review basis
- How to grow leeks — Royal Horticultural Society
- Vegetable gardening reference library — University of Minnesota Extension
Hardiness, harvest month, shank length and rust resistance depend on cultivar.