Growing Leeks in Scotland: The Complete Guide

Allium porrum

Leeks go into the ground in March and don't leave it until you lift them, sometimes out of frozen soil, the following February.

They're one of the few crops that suit this climate rather than merely tolerating it. They're hardy, they stand through a Scottish winter without protection, and they crop when little else does. The price is that they hold a bed for most of a year, and they have one real enemy here: rust.

Why leeks suit Scotland

The insect pests that trouble leek growers further south are largely warm-weather problems. Thrips, the main pest of commercial leek crops, do their worst damage in warm summers and are discouraged by rainfall. Allium leaf miner and leek moth are serious pests in England and Wales, and leek moth is spreading north, but neither is known to be established in Scotland yet.

What we get instead is rust, because it's driven by wet leaves, and we have plenty of those. Plan for rust and largely stop worrying about the insects.

Varieties

Nobody trials leeks for Scottish winters, so the pick is based on the trait that matters most here: standing in the ground through winter. All carry the RHS Award of Garden Merit, which is UK-wide and not a Scottish recommendation.

Also worth considering

The useful distinction is early against late. Early varieties tend to be taller and paler, with a longer white shaft; late varieties are shorter, darker and hardier. For Scotland the late ones are usually the better buy. Our best leek varieties for Scotland compares them all in more detail.

Soil and pH

Leeks want a sunny spot and free-drainingSoil that lets water pass through quickly rather than pooling, so roots aren't sitting in wet ground after rain. Full definition → soil, with a couple of bucketfuls of garden compost or well-rotted manure worked in per square metre. Avoid ground where onions, garlic or shallots grew recently.

They're also fussier about acidity than most vegetables. Leeks prefer soil around pH 6.5, and growth becomes increasingly restricted below 5.8. That matters here, because much of Scotland's soil is naturally acidic, especially in the wetter uplands. If your leeks come up thin and stay thin despite decent soil and steady watering, low pH is a likely culprit, and a cheap soil test will tell you. Our guide to Scottish soils covers testing and liming.

Sowing

Sow in March and April, or May and June for later-cropping varieties that stand into spring. You can start indoors from late winter for an earlier crop; keep those seedlings above 10°C and in good light. Sow about 1.5cm (¾in) deep, either in a seedbed or modulesA tray divided into small individual cells, each sown with its own seed or seedling, so each plant grows undisturbed roots until it's ready to plant out. Full definition → for moving later, which is the traditional approach, or straight into the final position. Expect about eight weeks from sowing to a plant ready to move.

Those are UK-wide months. In colder parts of Scotland the later end of each window is the safer bet, though leeks are forgiving about this in a way that tender crops are not.

Transplanting and puddling in

Move plants when they're about 20cm tall and pencil thick. The traditional method is called puddling inFilling a planting hole with water and letting it drain away before or after planting, to settle soil firmly around the roots and remove air pockets. Full definition →:

1. Make a hole about 15cm (6in) deep and 5cm (2in) across with a dibberA simple pointed hand tool used to make a planting hole in soil, for seedlings, sets or young plants. Full definition →.
2. Trim the roots back to about 2.5cm.
3. Drop one leek into each hole. Don't backfillThe soil (sometimes improved with grit or compost) used to fill the gap around a plant's roots after it's placed in its planting hole. Full definition → with soil.
4. Fill the hole with water. It settles a little soil around the roots and leaves the rest of the hole open.

Space plants 15cm to 20cm apart depending on variety, or about 10cm for baby leeks, with rows about 30cm apart.

Earthing up

Draw soil up around the stems several times as the plants grow. Keeping light off the lower stem is what gives the long white shank, and the extra soil steadies the plants against winter storms. Do it gradually, a little at a time, and don't let soil fall down between the leaves: it's gritty and almost impossible to wash out later. Earthing upDrawing soil up around a plant's base as it grows, most often potatoes, to keep light off developing tubers and support tall stems. Full definition → doubles as weed control and loosens the surface, so it's rarely wasted effort.

Watering and weeding

Water seedlings and new transplants until they're growing strongly. After that, leeks need water only in prolonged dry spells. Containers are the exception and need watering all season. Keep water off the foliage where you can: wet leaves are what rust needs.

Hoe between the rows, but weed by hand close to the plants, because the stems damage easily. Our article on organic and legal weedkillers weighs up hoeing, mulchingA layer of material spread over the soil around plants to suppress weeds, retain moisture, and improve soil structure as it breaks down. Full definition → and the chemical options.

Leek rust, the one that will find you

Bright orange pustules on the leaves are leek rust. In Scotland you should expect it rather than hope to avoid it, and knowing how it behaves takes most of the sting out.

• It infects best between 10 and 18°C, which is most of a Scottish summer.
• August to October are the worst months, exactly when leeks are bulking up here.
• Frost knocks it back, so winter works in your favour.
• It isn't in your soil. It survives only on living green tissue, so it carries over on standing crops rather than lurking in the ground.

Because leeks are in the ground almost year-round, one season's crop hands the rust straight to the next. Clearing old plants promptly, rather than leaving a few standing out of habit, breaks that chain. Give plants room for air to move between them, keep the foliage dry, and remove badly affected leaves. Rust is usually disfiguring rather than fatal: a rusty leek is still a good leek once the worst leaves are stripped off.

Resistant varieties help a little. RHS lists Oarsman as rust-resistant, while Teagasc, writing for commercial growers, says no variety is fully resistant, only less susceptible. Either way, airflow, spacing and clearing old crops are worth far more than the variety.

Rotation

Keep alliums moving around the plot, and allow four to five years before onions, garlic, shallots or leeks return to the same ground. That's longer than the usual four-year convention, because the allium diseases that matter stay in the soil for years once introduced.

Onion white rot is the worst of them. Leeks can catch it, though onions and garlic are the most susceptible. Its resting bodies survive in soil for at least 15 years, and there's no chemical treatment available to gardeners, so keeping it out of your ground in the first place is the whole game.

Don't grow chard among your leeks

In a Garden Organic members' trial, leeks grown with chard as a companion lost 69% of their marketable yield compared with leeks grown on their own. The chard seemed to reduce allium leaf miner, but not by a statistically significant amount. Low-growing clover as a companion made little difference either way.

Harvesting

Baby leeks are ready in a couple of months. Full-sized leeks take about six months, and you can start lifting from late summer while they're still small to spread the crop out.

Lift them gently with a fork rather than pulling, because the shank snaps more easily than you'd think. Late varieties can stay in the ground through winter into spring, lifted whenever you want them.

Leeks and the rest of the onion family are toxic to dogs, raw or cooked, so keep trimmings out of reach too. Our list of garden crops that are toxic to dogs has the rest.

Common problems

• Leek rust: orange pustules on the leaves, the main problem here.
• Bolting means the plant runs to flower. It's usually caused by low temperatures in spring, so watch for it after a cold one. Remove flower stalks as soon as they start to form.
• Onion fly maggots can kill seedlings outright and damage the roots and shank of mature plants. Insect-proof mesh over the row is the best defence.

Common questions

Sources