Growing Leeks in Scotland: The Complete Guide

Allium porrum

Everything you need to grow leeks in Scotland, from a March sowing to lifting them out of frozen ground in February. We have done the research so you don't have to.

Leeks are one of the few crops that genuinely suit this climate rather than merely tolerating it. They are hardy, they stand through a Scottish winter without protection, and they crop in the months when almost nothing else does. They are also slow, occupying a bed for the best part of a year, and they have one real enemy here. Almost everything below is about making that trade work in your favour.

Why leeks suit Scotland

The usual story on this site is that Scotland makes a crop harder. Leeks are the exception, and it is worth understanding why, because it changes what you should worry about.

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 both far more common in England and Wales than here, and it is genuinely unclear how established either is in Scotland.

What we get instead is rust, because it is driven by leaf wetness and we have plenty of that.

Varieties

Nobody trials leeks for Scottish winters, so the pick below is our judgement, reasoning shown. These 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, because standing through winter is the whole point of growing leeks here.

Soil, and the pH question

Leeks want a sunny spot and free-draining 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 are also fussier about acidity than most vegetables. Leeks prefer soil around pH 6.5, and growth becomes increasingly restricted below 5.8.

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. Sow about 1.5cm (¾in) deep, either in a seedbed for transplanting later, or straight into the final position.

Most people use a seedbed or modules and move the plants later, which is the traditional approach and works well. Expect roughly eight weeks from sowing to a transplantable plant.

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 are about 20cm tall and pencil thick. This is the step that produces the long white shank, and the method is unusual enough to be worth describing properly.

1. Make a hole about 15cm (6in) deep and 5cm (2in) across with a dibber.
2. Trim the roots back to about 2.5cm.
3. Drop one leek into each hole. Do not backfill with soil.
4. Fill the hole with water. That washes just enough soil down around the roots and leaves the rest of the hole open, which is what blanches the shank.

Space plants 15cm to 20cm apart depending on variety, or about 10cm for baby leeks, with rows around30cm apart.

Earthing up

Draw soil up around the stems several times as the plants grow, to keep light off the shank and lengthen the white part. Do it gradually, a little at a time.

The one thing to avoid is letting soil fall down between the leaves, which is gritty and almost impossible to wash out later. Earthing up doubles as weed control and loosens the surface, so it is rarely wasted effort.

Watering and weeding

Water seedlings and new transplants until they take hold. After that, leeks only need water during prolonged dry spells, which in most Scottish summers means rarely. Containers are the exception and need watering across the season.

Keep water off the foliage where you can. Wet leaves are what rust needs, and in a climate that supplies plenty of leaf wetness for free, there is no reason to add more.

Hoe between the rows, but weed by hand close to the plants. Leek stems bruise easily and damage lets rot in.

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 is not in your soil. It survives only on living green tissue, which means it carries over on standing crops rather than lurking in the ground.

That last point is the useful one. 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 enough 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 perfectly good leek once the worst leaves are stripped off.

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 is a longer gap than the usual four-year convention, and it exists because the diseases that matter here sit in the soil for years once introduced.

Onion white rot is the reason. It persists in soil for a very long time and there is no treatment for it, so keeping it out is the whole game. Leeks are less susceptible to it than onions are, which is a small mercy rather than a reason to relax.

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 are still small to spread the crop out.

Lift them gently with a fork rather than pulling, because the shank snaps more easily than you would think. Late varieties can be left standing through winter into spring and lifted whenever you want them. There is no need to store leeks: the garden is the store, which in February is worth a great deal.

Common problems

• Leek rust is the main one here, covered above.
• Onion white rot persists in soil for many years and cannot be treated. Rotation is the only real defence.
• Allium leaf miner and leek moth are serious problems in England and Wales. How far either is established in Scotland is genuinely unclear, so we would not fit mesh against them here without seeing damage first.
• Bolting means the plant runs to flower and the shank goes woody. Usually a response to stress or a cold check after transplanting.

Common questions

Sources