When to plant leeks in the UK splits into two jobs. Sow the seed between March and April, then plant the young leeks out into their final position from May into June. That is the whole timetable. Leeks are a long-season crop that sits in the ground for the best part of the year, sown in spring and lifted right through autumn and winter, and getting those two dates roughly right is what gives you thick, well-blanched leeks to pull on a cold January day rather than thin, disappointing ones. Sow too late and they never bulk up before winter.

Leeks are the crop that fills the hungry gap for me, the stretch of winter when there is little else worth pulling from the garden. They ask for patience more than skill, because they are in the ground so long, but there is almost nothing to go wrong once they are established. I have grown them on heavy Oxfordshire clay for two decades, and the only year they truly let me down was the year I sowed them late and rushed, which taught me the one lesson that matters most: leeks want to go in early.

Why Timing Matters So Much for Leeks

Leeks are slow. From sowing to a decent-sized leek is around thirty weeks, which is most of the growing year, so every week you delay the sowing is a week knocked off the end when the plant should be bulking up. A leek sown in March has the whole season to build a thick shaft. One sown in late May is always playing catch-up, and it shows on the plate.

The flip side of that slowness is toughness. Leeks are properly hardy, standing through frost and snow without a flicker, which is exactly why they are worth growing. They give you fresh vegetables from the garden in the depths of winter when the shop prices climb and everything else has gone over. Get them started in good time and they will feed you from autumn right through to spring.

Month by Month

March and April: sow the seed

This is the main sowing window and the one date that really matters. Sow indoors in trays or modules from early March, or into a spare corner of the garden as an outdoor seed bed once the soil is workable, usually late March into April. Indoors gives you a few weeks’ head start and is my preference on cold clay, where the outdoor soil takes an age to warm. The seedlings come up looking like fine blades of grass, and they are slow, so do not panic when nothing much seems to happen for a while.

May and June: plant them out

When the young leeks are about the thickness of a pencil and 20cm or so tall, they are ready to move to their final position. That is usually May into June. This is the classic leek job that looks odd the first time you do it: you drop each seedling into a deep hole and water it in rather than firming soil around it, which I will come to below. Plant out on time and the leeks have the whole summer and autumn to thicken up.

July onwards: too late for a main crop

By July it is too late to start leeks for a proper winter crop, because they simply will not have the season left to bulk up. If you have missed the window, do not force it. Sow something quick instead, and come back to leeks next March. There is no rushing a long-season crop.

Where You Garden Shifts the Dates

The dates above suit the middle of the country. In southern England and milder spots you can sow a little earlier and get away with a slightly later planting out, and the season stretches further at both ends. Across the Midlands the standard dates apply as written.

In northern England and Scotland, where springs are colder and shorter, starting leeks indoors makes even more sense, since it gets them going while the outdoor soil is still too cold. Push the sowing to late March and the planting out towards June, and choose a hardy late variety that will stand a hard northern winter. Leeks are one of the crops that genuinely earn their place in a cold garden, because they keep giving when almost nothing else will. The wider picture of what goes in when sits in the vegetable planting calendar.

Soil and Position

Leeks are not especially fussy, but they do best in an open, sunny spot in soil that has been improved with plenty of well-rotted organic matter. Rich, moisture-holding ground that does not sit waterlogged is what they want, and dig in some compost before planting if you can. My guide to improving garden soil covers how, and if your ground stays wet through winter, when the leeks will still be standing in it, sorting the drainage first pays off.

Avoid freshly manured ground and heavy compaction. On badly compacted soil the roots struggle and the plants sulk, which is worth reading up on in soil compaction in UK gardens if yours sets hard. A sheltered spot helps too, since tall leeks can rock in strong wind, which loosens the roots.

Planting Out: the Dib and Puddle Method

This is the one genuinely unusual thing about growing leeks, and it is worth doing properly because it is what gives you that long, white, tender shaft rather than a mostly green stick. Make a hole about 15cm deep with a dibber or a thick stick, spacing the holes around 15cm apart with 30cm between rows. Drop one leek seedling into each hole, right down to the base.

Then, and this is the part that feels wrong the first time, do not fill the hole with soil. Instead, water each one in, which washes just enough soil over the roots to settle the plant while leaving the hole to fill in gradually on its own. The deep hole blanches the lower stem white as it grows. Before planting, some people trim the tips of the leaves and roots, which does no harm and makes the seedlings easier to handle, though I often skip it. Water them in well and keep them watered until they are clearly growing away.

Watering, Feeding and Earthing Up

For the first few weeks after planting, keep the leeks watered while they establish, because a leek that dries out badly at this stage never quite recovers its vigour. Once away, they are fairly self-sufficient, though a good soak in a dry summer spell keeps them growing steadily rather than stalling. My guide to how often to water covers the balance, and if yours seem to be sitting still, why vegetable plants grow slowly is worth a read.

Feeding is light. If the ground was well prepared they need little, though a balanced feed in mid summer does no harm on poorer soil. The one job worth doing is earthing up: drawing a little soil up around the stems every few weeks through the season, which lengthens the blanched white part that is the best bit of a leek. Do not let soil fall down into the centre of the plant, which leaves grit between the leaves.

Growing Leeks in Containers

Leeks can be grown in a large, deep container, and it works better than you might expect for a crop with such a long season. You will not match the yield of open ground, but a decent tub of leeks is a fine thing on a patio, and the depth is what matters, since leeks need root room and something to blanch into.

Use as big a container as you can, keep it consistently watered, since pots dry out faster than beds and leeks hate drying out, and go for one of the smaller, quicker varieties rather than a giant show type. The general principles are in growing vegetables in pots.

How Long They Take, and When to Harvest

Leeks take roughly 30 weeks from sowing to a usable size, so a March sowing gives you leeks to start pulling from around September or October, running on right through the winter. There is no single harvest day. You lift them as you need them, taking the biggest first and leaving the rest to keep growing.

To harvest, ease each leek out with a fork rather than yanking it, since the roots hold on hard and the shaft snaps if you pull. And here is the real beauty of the crop: leeks can stay in the ground all winter and be pulled fresh whenever you want them, no storing required. They stand through frost and snow perfectly happily, and a leek lifted straight from frozen ground in January is as good as it gets. Only towards spring, as they think about running to seed and sending up a flower spike, do they start to toughen, so use them up before then. The full growing detail beyond timing lives in how to grow leeks in the UK.

The Mistakes That Spoil a Leek Crop

Three things account for most leek disappointment, and the biggest is sowing too late, which leaves the plants no time to bulk up before winter and gives you thin, pencil leeks. The second is poor establishment, where seedlings that were not kept watered after planting out sit and sulk rather than growing away. The third is planting too shallow, so you get short green leeks instead of the long white shaft, which the deep-hole method solves.

Get those right and leeks are close to foolproof. They ask for an early start, a deep planting hole and a bit of water while they settle, and in return they stand in the garden feeding you through the leanest months of the year.

What Goes In Alongside Leeks

Leeks are alliums, close cousins of onions, but far more forgiving and better suited to a wet British winter, since onions need to be lifted and stored while leeks simply stand in the ground. They fit naturally alongside the other hardy crops that see you through the cold months, like cabbages and the roots.

Sow them in spring alongside your carrots and other early crops, and by the time those have been eaten the leeks are just coming into their own for winter. If you are filling the autumn beds as the summer crops finish, my guide to what to sow in September pairs well with a standing row of leeks.

When to Plant Leeks in the UK: Frequently Asked Questions

A Sensible Place to Start

If you take one thing from this, let it be that leeks want an early start. Sow a tray of seed in March, keep the seedlings ticking over, and plant them out into deep holes in May or June. That single early sowing is most of the job, and leeks are forgiving enough that a first attempt almost always gives you something to pull.

Then simply be patient. Leeks reward the long wait like few other crops, standing in the ground through the worst of the winter and giving you fresh vegetables when the garden has otherwise gone quiet. Start early, plant deep, keep them watered while they settle, and you will be pulling leeks on frosty mornings long after everything else has finished.