Leeks are sown in spring, planted deep by June and dug all winter

Leeks are sown in late winter or spring and planted out in late spring or early summer. In the UK, sow indoors from late January to early March, or outdoors in a seedbed from early March to mid-April, then move the young plants to their final spot from early April to late June.

They’re slow. Expect 140 to 180 days from sowing to the first harvest, which is why leeks are one of the few crops you plant in June and still eat in March.

Sowing indoors or outdoors

Indoor sowings in late January or February give the biggest, earliest leeks. Sow thinly, 1 cm deep, in a seed tray or deep module in a cool greenhouse or on a bright windowsill. They don’t need much heat, and they grow better cool than warm.

Outdoor sowing is easier and works well if you don’t need leeks until winter. From early March to mid-April, rake a small seedbed and sow a short row 1 cm deep. You only need a metre or so of row to raise enough plants for most gardens. Thin the seedlings to a couple of centimetres apart so each has room to thicken.

The dates here are for a typical lowland garden in England or Wales, with a last frost around 20 April. In Scotland, the north of England and frost pockets, sow outdoors towards the end of the window. In the south-west, near the coast and in cities you can start earlier. Leeks are tough enough that a late frost won’t harm the seedlings.

Planting out

Leeks are ready to move when they’re about pencil thick and 15 to 20 cm tall, usually from early April onwards for indoor sowings and from May or June for seedbed ones. Water them well the day before, then lift them gently with a fork.

1. Make holes about 15 cm deep with a dibber or a thick stick, 15 cm apart in rows 30 cm apart.
2. Drop one leek into each hole, so only the top few centimetres of leaf show.
3. Don’t fill the hole with soil. Fill it with water instead, which settles a little soil over the roots.
4. Leave the holes open. They fill in by themselves over the next few weeks.

Planting deep is what gives you a long white stem. The part of the leek that grows in the dark stays pale and tender. You can lengthen it further by drawing soil up around the stems once or twice in late summer.

On a raised bed or in square-foot gardening, you can fit nine leeks in a 30 cm square. They’ll be a little slimmer, which plenty of cooks prefer.

Where to put them

Leeks want full sun and soil with some compost or well-rotted manure dug in. They’re in the onion family, so rotate them with onions, garlic and shallots and keep them off ground that had any of those in the last couple of years. See crop rotation for beginners if you’re planning beds for next year.

Carrots and celeriac make good neighbours. Keep leeks away from peas and beans of all kinds.

Harvesting

Leeks are ready from early September and keep going until early April, so they carry on into early spring, when little else is ready. Ease them out with a fork rather than pulling, or the stem may snap. Most varieties stand in the soil all winter without harm, so dig them as you need them.

Early varieties are better for autumn, while hardier winter types with darker, blue-green leaves are better for standing through to spring. Growing a few of each spreads the harvest.

Common problems

Leek rust. Orange spots on the leaves in late summer, worse in damp weather and on soil short of potassium. It looks bad but rarely spoils the stem. Give plants the full spacing and remove the worst leaves.

Allium leaf miner and leek moth. Both tunnel into the stems and leave them twisted or rotten. Covering plants with fine insect mesh from planting time is the most reliable protection.

Bolting. A flower stalk in spring means the leek has finished. Use bolted leeks quickly, as the centre turns woody.

Thin, weak plants. Usually late planting or poor soil. Get them in by late June and water well in dry spells over summer.

You can see leeks alongside everything else that’s in season on our sowing calendar, or open the leek page for spacing and companions at a glance.