Bolting
A cold spell over young plants can make them flower in summer instead of thickening. Cover early outdoor sowings if the temperature drops, and do not plant out tiny seedlings into a freeze.
UK crop guide
Leeks
Leeks are the crop that is still there in January. They grow slowly, they stand frost, and a late variety can be lifted whenever you need it from autumn into spring.
The RHS sows them in spring, in the ground or in a seedbed, and also indoors in late winter for an earlier transplant. Baby leeks are ready in a couple of months. A full-sized leek takes about six.
- Sow in February, March and April. Indoors in late winter, or outdoors in spring in a drill about 1.5cm deep. Gardeners' World also lists leeks among the April sowings under cover.
- Plant out in April, May and June. Indoor sowings can go out in mid to late spring. Plants from a seedbed are moved once they are large enough, into early summer.
- Harvest in August, September, October, November, December, January, February, March and April. From late summer as baby leeks, then through winter and into spring for later varieties.
Sow indoors
A late-winter sowing in modules or a tray, kept under cover, can be planted out in mid to late spring. This is the route for an earlier leek, and it is useful if your outdoor seedbed stays cold and wet. Gardeners' World includes leeks with the crops sown under cover in April as well, so a second batch is still worth making.
Sow or plant outdoors
The traditional sowing is a seedbed in spring. Make a drill about 1.5cm deep, water it, and sow thinly. Further rows sit about 30cm apart. If a cold spell arrives, cover the bed. The RHS warns that cold at this stage can make the plants bolt later.
You can also sow straight into a large deep container if you only want baby leeks. A pot about 40cm wide might hold four or five full-sized plants if you look after the watering.
Plant out
Make holes with a dibber or a trowel handle, about 15cm deep and 5cm across. Space them 15 to 20cm apart, or 10cm if you plan to eat them as babies, with 30cm between rows. Lift the seedlings, trim the roots back to about 2.5cm, and stand one leek in each hole.
Fill the hole with water rather than soil. The RHS calls this puddling in. The water settles a little soil around the roots, and there is no need to backfill. The hole fills itself as you hoe through the summer, and the buried shank is the long white part you want.
Indoor-raised plants can move in mid to late spring. Seedbed plants often go out a bit later, once they are about pencil thick. Water them in a dry spell while they establish.
Spacing and depth
- Final spacing
- 15 to 20cm apart, rows 30cm apart
- Baby leeks
- 10cm apart
- Planting hole
- About 15cm deep, watered in, not backfilled
- Seed drill
- About 1.5cm deep
Harvest
Start lifting in late summer while some plants are still small, and leave the rest. A fork is safer than a pull, because the shaft goes deep. Late varieties stay in the ground through winter and into spring. Frost can improve the flavour.
Take alternate plants if you want some baby leeks and some full ones from the same row. They do not all have to be harvested on one day.
Common problems
Rust
Bright orange spots on the leaves are leek rust, a common fungus that also hits garlic and onions. It looks worse than it is. The shank underneath is still edible. Give plants the spacing above so air can move, and avoid wetting the leaves more than you have to.
Allium leaf miner
The same leaf-mining fly that affects onions will bore into leeks. It is established across much of England and parts of Wales. Insect-proof mesh over the bed, from planting onwards, is the practical cover on an allotment.
What you'll need
Kit for this crop, based on the method above.
- Peat-free seed compost
A fine compost for modules and small pots. The RHS recommends peat-free mixes.
- Module trays or small pots
For crops started under cover. Deep pots suit peas, beans and sweetcorn.
- Dibber
For leek holes about 15cm deep. A trowel handle will do.
- Horticultural fleece
For early sowings and for covering tender plants if a late frost is forecast.
- Insect-proof mesh
The RHS found a full cover is the most effective defence against carrot fly, and it also keeps pigeons and caterpillars off brassicas.
- Fork
For lifting roots and potatoes without spearing the crop.
- Labels
Variety and sowing date, so succession sowings do not get mixed up.
Common questions
Do I fill the leek hole with soil?
No. Stand the leek in the hole and fill it with water. The RHS calls this puddling in, and says there is no need to backfill. Soil falls in gradually and the white shank lengthens.
Can leeks stay in the ground in winter?
Yes. Late varieties are meant to. Lift them when you want them, from autumn through to spring. A hard frost will not finish the crop, and the RHS notes it can make the flavour sweeter.
On the calendar
Related crops
Sources
- RHS: How to grow leeks. Checked 11 October 2026.
- RHS: How to grow onions. Checked 11 October 2026.
- BBC Gardeners' World: Your seed-sowing year. Checked 11 October 2026.