Leek

About

Leeks are the crop that fills the hungry gap. They stand in the ground through the whole of a British winter, unbothered by frost, snow or waterlogging, and you lift them as you need them from November until March, when there is very little else to lift.

The technique that makes them worth growing is one of the odder jobs in the kitchen garden. You make a deep narrow hole with a dibber, drop a seedling in, fill the hole with water and walk away. The soil washes in around the roots on its own, and the loose earth in the hole gives the long blanched white shank that is the only part most people want.

Everything else is straightforward. Firm soil, steady watering, and a watch for leek moth, which has spread rapidly across Britain in the last twenty years.

Appearance and character

A biennial grown as an annual, forming a fan of leaves above a thick cylindrical stem, and reaching 40 to 60 cm.

The edible part is not a bulb. It is a shank of tightly rolled leaf bases, which is why a leek is solid all the way through and why it does not swell like an onion.

Leaves are flat, broad and strap-shaped, folded along the midrib, and range from mid-green to a strong blue-grey depending on variety. They fan out in a single plane rather than all round.

The white section is created by exclusion of light, either by planting deep or by drawing soil up around the stem. A leek grown on the surface is green almost to the base.

Flowers appear only in the second year if the plant is left, a dense globe of pale purple on a stem up to 1.5 m, and they are worth leaving for the bees on a plant that has bolted anyway.

Varieties divide by season. ‘Zermatt’ and ‘Pancho’ are early and slim for autumn, ‘Musselburgh’ is the reliable maincrop, and ‘Bandit’ and ‘Apollo’ stand hardest through late winter.

Where it is from

The eastern Mediterranean and the Middle East, derived from the wild Allium ampeloprasum, which still grows around the Mediterranean and on a few British cliffs.

Cultivation is ancient. Leeks were grown in Egypt and Mesopotamia, they appear in the Bible, and the Roman emperor Nero was mocked as Porrophagus, the leek-eater, for eating them to improve his voice.

The Romans brought them to Britain, and the leek became a staple of the medieval poor because it stands through winter and needs no storage.

The Welsh association is old and its origin unclear. One account has Welsh soldiers wearing leeks in their caps at the battle of Heathfield in 633 to distinguish themselves, and Shakespeare treats the custom as long established.

The plant’s tolerance of cold and wet is what earned it its place, and it is the reason a British allotment still grows them.

How it grows

Sow seed in a seedbed or in modules from February to April, thinly, about 1 cm deep. A February sowing under cover gives the longest season.

Transplant when the seedlings are pencil-thick and about 20 cm tall, usually in June.

Trim the roots to about 2 cm and the leaf tips by a third before planting, which makes handling easier and reduces water loss.

Dib and drop. Make a hole 15 to 20 cm deep with a dibber, drop one seedling in so it hangs by its leaves, and fill the hole with water. Do not backfill with soil. The watering washes enough earth around the roots, and the space in the hole is what produces the long white shank.

Space plants 15 cm apart in rows 30 cm apart. Closer spacing gives more, smaller leeks, which many people prefer.

Plant into firm ground. Leeks want soil that was manured the previous autumn and has settled, rather than freshly dug fluffy ground.

Earth up from late summer if you want more white, drawing dry soil up around the stems a little at a time. Take care not to let soil fall between the leaves.

Water steadily through summer. A check to growth is what causes bolting.

Lift from November onward with a fork, working the plant loose rather than pulling, since the shank breaks.

Leave the rest in the ground. Leeks store better in the soil than anywhere else and stand until March.

Through the seasons

Winter is harvest and sowing. Lift as needed from November through to March, and start the first sowing under cover in February.

Spring is sowing and growing on. Sow outdoors from March, and keep the seedbed weeded and watered.

Summer is transplanting. Move the seedlings into their dibbed holes in June, water them in, and watch for leek moth from May.

Autumn is earthing up and the first pull. Draw soil up around the shanks, and start lifting early varieties from October.

Care difficulty

Easy. Leeks are among the most forgiving vegetables and they occupy ground for a long time, which is the main cost of growing them.

The transplanting method looks strange and is the whole technique.

Leek moth has changed the picture in the last two decades. It was confined to the south coast and is now found across most of England and into Wales and Scotland, and it is the pest most likely to spoil a crop.

Rust is common in mild wet summers and is usually survivable.

Frost, snow and wet do nothing to them at all.

Watering

Water the seedbed and the modules consistently while the plants are small.

Water thoroughly after transplanting, which is what settles the soil around the roots.

Water weekly in dry weather through summer. Steady growth is what prevents bolting.

Reduce watering in autumn as growth slows.

Mulch between the rows to hold moisture and suppress weeds, keeping the mulch away from the shanks.

Warning signs, diseases and pests

Leek moth is the pest to know about now. Small caterpillars mine inside the leaves, leaving whitish windowpane streaks, then tunnel down into the shank where they cause rotting. There are two generations, from May and from August. Cover the crop with insect-proof mesh from May, which is the only reliable defence, and remove and destroy affected plants. Rotate the ground.

Allium rust produces bright orange pustules on the leaves, worst in mild wet summers and on plants fed too much nitrogen. It looks alarming and a moderate attack barely reduces the crop. Remove badly affected leaves, avoid overhead watering, space plants more widely, and do not compost the debris.

Allium leaf miner leaves lines of white dots on the leaves in spring and autumn, and the larvae tunnel into the shank. Mesh is again the defence.

White rot is the serious soil disease. Leaves yellow and wilt, and the base of the plant carries a fluffy white fungal growth with small black dots. It persists in soil for fifteen years or more. Destroy affected plants, never compost them, and do not grow any allium on that ground again.

Bolting, where a flower stem rises in the first year, follows a check to growth, usually cold or drought after transplanting. The plant is still edible if used promptly.

Thin weak plants usually mean loose soil, poor spacing or competition from weeds.

Growing environment

Full sun to light shade. Leeks tolerate less sun than most vegetables.

Deep, fertile, firm, well-drained soil. Dig in well-rotted manure the previous autumn and let the ground settle.

Avoid freshly dug loose ground, which gives poor anchorage and thin shanks.

Rotate the ground. Do not follow onions, garlic or leeks with more alliums, both for rust and for white rot.

Allow 15 cm between plants and 30 cm between rows, and expect them to occupy the bed from June until March.

Insect-proof mesh over the crop from May, which is now close to essential in most of England.

They grow well in a deep raised bed and poorly in containers, since the roots want depth and firmness.

Feeding

Dig in well-rotted manure or compost the previous autumn. That is the main feed.

A nitrogen-rich feed in midsummer helps a crop that is growing slowly.

Stop feeding by late summer. Soft late growth is more prone to rust and to rot.

Avoid heavy nitrogen through the season, which produces lush leaves, thin shanks and worse rust.

A dressing of sulphate of potash in autumn improves winter hardiness.

Troubleshooting

Why do I fill the hole with water instead of soil? The water washes just enough earth around the roots to hold the plant, and the empty space in the hole is what lets the shank swell long and white. Backfilling with soil gives a shorter, greener leek.

How do I get a longer white section? Plant deeper, and earth up from late summer by drawing dry soil around the stems a little at a time.

Whitish streaks in the leaves and rotting shanks. Leek moth. Cover the crop with insect-proof mesh from May, destroy affected plants, and rotate.

Bright orange spots on the leaves. Allium rust. A moderate attack does little harm. Remove the worst leaves, space plants more widely, avoid nitrogen and do not compost the debris.

A flower stem has appeared in the first year. Bolting, caused by a check to growth from cold or drought. The leek is still usable if you eat it soon.

Fluffy white growth at the base with black dots. White rot. Destroy the plants, never compost them, and grow no alliums on that ground again for many years.

When can I start lifting them? From October or November for early varieties, and through to March for late ones. They keep better in the ground than out of it.

Are leeks safe for my dog? No. Like all alliums they damage red blood cells in cats, dogs and horses, and cooking does not help. Keep trimmings and leftovers out of reach.