Leeks are one of the most dependable crops you can grow. Plant them in spring, leave them to thicken up quietly through summer, and they reward you with a steady supply of sweet, mild stems right through the coldest part of the year.
The headline with growing leeks is that they take a long time but very little effort. A spring sowing will not be ready for around six months, but in return you get a crop that asks almost nothing of you over winter and stands happily through frost, often tasting all the sweeter for it. Get them off to a good start and the rest looks after itself.
Starting leeks off in the greenhouse
A greenhouse is the perfect place to raise young leeks for a strong, early start. Sowing under cover from late winter lets you get plants going well before the soil outside has warmed up, and keeps tender seedlings safe from cold snaps and slugs while they bulk up. Think of the greenhouse as a nursery here: you raise the young plants on the bench, then move them outside to grow on to maturity. Even a compact patio greenhouse or a bright windowsill is enough to get a tray of leek seedlings underway.
Growing leeks from seed
Growing leeks from seed is the cheapest and most rewarding route, and a single packet of leek seeds will give you far more plants than most households need. The trade-off is patience, as leeks are slow growers, but they need almost no fussing while they get there.
The prime months for sowing leeks are February to April, but you can go as late as June. Just be careful of extreme heat. Under cover you can start them off in February or March in small pots or modular trays of moist, peat-free seed compost, sowing the seeds thinly about 1 to 1.5cm deep. Outdoors, the traditional method is to sow into a dedicated seedbed in March or April, in a shallow drill around 1 to 1.5cm deep, then transplant the young plants to their final positions later. Sowing into modules or a seedbed rather than straight into their final spacing keeps your best growing space free for faster crops in spring.
Keep the trays somewhere warm, ideally above 10°C, and in good light, and keep the compost just moist. Greenhouse shelving or a seedrack lifts your trays off a cold floor and keeps the leek seedlings close to the light, which stops them growing thin and leggy. Move plants into larger pots if roots start to show through the drainage holes. Your young leeks are usually ready to plant out after about eight weeks, once they are roughly 20cm tall and about as thick as a pencil.
Growing from young plants
Garden centres sell young leeks as bundles of bare-root seedlings or in modules in spring and early summer, ready to plant straight out. The choice of varieties is more limited than with seed, but it is a quick, reliable way to get a row going, especially if you missed the main sowing window or only want a handful of plants.
Whether you raise your own from leek seeds on the staging or buy young plants in, the goal is the same: sturdy little leeks about pencil thick and 20cm tall, ready to drop into their final home. Look for varieties with an RHS Award of Garden Merit for reliable results, and pick early, mid-season or late types (or a mix) depending on whether you want to harvest from autumn, through winter, or into spring.
Hardening off and transplanting
Before leeks raised indoors go outside, acclimatise them to outdoor conditions over a week or two by hardening them off, moving them out by day and back under cover at night, or standing them in a cold frame with the lid open in mild weather. Plants grown outdoors in a seedbed can be lifted and moved straight to their final bed.
Transplanting is where leeks get their signature long white base, or shank, and the technique is wonderfully simple. Once your plants are readyl, usually from June into July, make a row of deep holes with a dibber or trowel handle, about 15cm deep and 5cm across. Lift each young leek, trim the roots back to about 2.5cm if you like, then drop one plant into each hole.
Top Tip: Rather than backfilling with soil, simply fill the hole with water. This is known as puddling in: the water settles enough soil around the roots to anchor the plant, while the deep hole and loose fill blanch the lower stem, keeping it tender and white. There is no need to firm soil back into the hole.
Growing leeks in raised beds and the ground (from seed and plants)
Leeks do best in deep, rich, firm soil, which makes a raised bed an excellent home for them. A bed gives you full control over the soil, easy access for earthing up, and good drainage, all of which suit a long-season crop that sits in the ground for months. Whether you are working in a raised bed or open ground, the principles are the same: a sunny, fertile, well-prepared site that you do not need for quicker crops.
Where to position them
Choose an open, sunny site with fertile, free-draining soil, where you have not grown leeks, onions or other alliums for at least a couple of years, to avoid any build-up of soil-borne disease. Weed the ground thoroughly and dig in a couple of bucketfuls of well-rotted manure or garden compost per square metre before planting, then rake it level and firm. Leeks like a fertile but firm soil that holds them steady through autumn gales, so avoid very loose, fluffy ground. If you garden no-dig, simply mulch the surface with organic matter and plant into that.
Watering, soil, spacing and blanching
Spacing is straightforward. When transplanting, set the plants about 15cm apart, with rows roughly 30cm apart. Closer spacing of around 10cm gives you slimmer baby leeks, while a little more room produces fatter stems. Whatever the spacing, the deep dibber holes do the important job of starting that long white shank, since the soil that gradually washes and falls in around the stem keeps it shaded and pale.
Water leek seedlings and newly planted leeks until they are established and growing away strongly. After that, you only need to water in prolonged dry spells.. Collecting rainwater in a water butt gives you a free, soft supply for those dry summer weeks. Keep the bed weed-free, hoeing carefully between rows and hand-weeding close to the stems so you do not nick them.
Top Tip: For the longest, whitest shanks, earth up your leeks as they grow. This simply means drawing dry soil up around the stems a little at a time over the season to exclude light, taking care not to let soil tumble down between the leaves.
Leek companion plants
A little companion planting helps a leek bed earn its keep. The classic partner is the carrot: leeks are thought to confuse and deter carrot fly, while carrots in turn help mask leeks from onion and allium pests, so the two grow happily side by side. Celery and beetroot also make good neighbours, and the strong scent of leeks can help keep some pests away from nearby crops.
Avoid planting leeks next to other alliums such as onions and garlic, as they compete for the same nutrients and share the same pests and diseases. It is also best to keep leeks away from peas and beans, which can inhibit each other's growth.
When and how to harvest
Knowing when to harvest leeks is reassuringly relaxed: lift them whenever you want them. Baby leeks can be pulled after just a couple of months, while full-sized leeks take around six months, so a spring sowing is typically ready from October onwards. Gently ease each plant out with a fork rather than tugging, as the roots hold on firmly. Harvesting alternate plants along the row leaves the rest more space to keep swelling. Hardy winter varieties stand happily in the ground from autumn right through to April, with no need for protection, and a touch of frost often makes them sweeter. Leeks growing alongside your potatoes, asparagus and spinach round out a veg patch that crops across the whole year.
Flowing Leeks
A lesser known fact is that leeks are hardy biennials. They spend their first year growing as you or I best know them for, the vegetable to eat, then flower and produce their seeds in the second year. The flowers are beautiful and are excellent pollinators - consider keeping a few in the bed, harvest the seeds and plant those the year after!
Leek pests and problems and how to avoid them
Leeks are relatively trouble-free, but a few pests and diseases are worth knowing about, and most can be headed off with good housekeeping rather than chemicals.
Allium leaf miner and leek moth are the two main insect pests. The larvae of both bore into the stems and leaves, causing rotting and distorted growth. The simplest, most reliable defence is to cover your leeks with insect-proof mesh or fine horticultural fleece from spring onwards, which physically keeps the egg-laying adults off the crop. Rotating where you grow your alliums each year also helps break the cycle.
Leek rust shows up as bright orange pustules on the leaves, encouraged by damp, crowded conditions and excess nitrogen. Avoid wetting the foliage when you water, space plants well so air can circulate, and choose rust-resistant varieties if you have had it before. Mild cases rarely ruin the crop, as the white shank is usually still perfectly good to eat.
Onion fly and white rot are soil-borne problems shared with the wider onion family. Onion fly maggots attack the roots and base, while white rot causes yellowing leaves and a fluffy white fungus on the roots. There is no cure for white rot, so prevention through crop rotation is everything: never grow leeks, onions or garlic in the same ground year after year, and avoid bringing in soil or plants from an infected plot.
Finally, watch for bolting (premature flowering), which can be triggered by a cold spell after sowing. Protect early outdoor sowings with cloches or fleece in cold weather, and remove any flower stalks as soon as they appear, as flowering turns the centre of the leek tough and fibrous.
Cooking with leeks
Leeks are one of the kitchen's great quiet workhorses, sweet and gentle where onions are sharp. They are wonderful softened slowly in butter, stirred through soups and stews, braised whole, or simmered into the great British classic, leek and potato soup. Chef Gill Meller has shared a lovely leek recipe on the Rhino blog that shows them off beautifully:
You will find plenty more seasonal ideas over on the Rhino recipes from the garden, with new dishes added regularly through the year. Before cooking, always slice your leeks and wash them well in cold water, as a little grit likes to hide between the layers.
Growing leeks is a long, slow pleasure, but a rewarding one. Get them started under cover, drop them into their dibber holes, then leave them to stand through the cold months and lift them fresh whenever the kitchen calls. Few crops give you so much for so little fuss across the depths of winter.