How to Grow Leek

Allium ampeloprasum · Also called: Porrum, Poireau, Lauch, Porree, Prei, Puerro, Porro, Garden leek

Thin leek seedlings emerging from dark soil, each bent over in a loop before straightening.

Photo: Rasbak, CC BY-SA 3.0 (Wikimedia Commons)

A leek is two useful things at once. It is a vegetable that is paid for by the length of the white part at its base, and that white is not something the plant grows on its own — it is something the grower makes, by keeping light off the stem. Learn that one trick and the same crop is worth considerably more. It is also, almost uniquely among vegetables, its own store. A leek will stand in the ground through hard frost and wait, so a grower lifts only what can be sold this week and leaves the rest growing. Most vegetables force you to sell when they are ready. This one lets you sell when the price is right, and for a small farmer that is a rare kind of freedom.

Growing Leek, Stage by Stage

1. Get the land ready — Deep, rich, well-drained ground with no onion history.
2. Sow the seed in a nursery — Raise them thickly in a small bed until they are as thick as a pencil.
3. Transplant deep, and make the white — Drop each seedling into a deep hole. This one step is where the value comes from.
4. Weed, water and feed — A thin upright plant cannot shade out a weed, so you must.
5. Watch for trouble — Rust on the leaf, grubs inside the stem, and white rot in the soil.
6. Harvest: lift, do not pull — A leek snaps if you pull it. Loosen the soil first, every time.
7. Keep them in the ground, and sell — The best store for a leek is the field it grew in.

Common Problems & Troubleshooting

If you see: Leeks with only a few centimetres of white at the base and a long green stem above it.

It likely means: They were not planted deep enough or not earthed up. The white is made by keeping light off the stem, and nothing else creates it.

Do this: Plant into a hole about fifteen centimetres deep, not into a shallow one.

If you see: Leeks breaking off at the base as they are harvested, leaving the bottom in the ground.

It likely means: They were pulled instead of lifted. A leek is held firmly and its shank is brittle, so firm ground wins every time.

Do this: Push a fork in beside the plant and lever the soil loose before touching the leek.

If you see: Bright orange powdery spots and streaks over the leaves, worst in mild damp weather.

It likely means: Rust. It is the commonest disease of this crop and it is worse where plants are crowded, soft with nitrogen, and slow to dry.

Do this: Space plants properly so that air moves between them.

If you see: Plants yellowing and wilting in patches, lifting easily, with a soft base carrying white fluffy growth and tiny black grains.

It likely means: White rot. It is the most serious disease of the onion family and the small black grains survive in the soil for fifteen years or more.

Do this: Remove and burn every affected plant, and never compost them or leave them on the field.

If you see: Pale winding tunnels in the leaves, small grubs in the heart, and rotting damage running down into the shank.

It likely means: Leek moth or allium leaf miner. Both lay on the leaves and the grubs work downwards into exactly the part that is sold.

Do this: Cover young crops with fine netting, since the adults must land on the plant to lay.

If you see: A hard round stalk pushing up through the middle of the leek, with a ball of buds at the top.

It likely means: The plant has decided to flower, usually after a cold spell while young or simply because it has been left too long.

Do this: Lift those plants first, since they only get woodier.

Yield & Market Value

Growing the crop is only part of the job. The last part is knowing what a normal harvest looks like where you are, and knowing what your leeks are worth before you agree a price with anybody.

Remember It This Way

If you forget every other page of this guide, keep these lines. They are the whole crop, in order, short enough to carry in your head.

Never after onion, garlic or leek. Three or four years clear.
Raise them in a nursery until they are as thick as a pencil.
Make a deep hole. Drop the seedling in. Only the tips show.
Do not fill the hole. Pour water in instead.
The white is the part light never reached. You make it.
Weed often. A thin upright plant shades nothing.
Keep the water steady or the stem stays thin.
Do not let soil fall down between the leaves.
Lift with a fork. Never pull, or it snaps.
Leave the rest standing. The field is the best store.

Test Yourself: Identification

What do the seedlings look like?

How should a young plant sit in the ground?

When is the crop ready to lift?

Honest Limits of This Guide

Timings here are given by season and by the state of the plant rather than in named months, because leeks are grown in both hemispheres and in tropical highlands. Count from your own sowing.
The two names in the botany section are both real. GBIF treats the leek as part of Allium ampeloprasum and does not hold Allium porrum as an accepted species, while EPPO keeps ALLPO for it. This guide reports both rather than choosing one and pretending the other does not exist.
Two ways of making the white shank are given, the deep hole and earthing up along a furrow, because both are widely used and neither is better everywhere. Which suits you depends on your soil and on whether you are working by hand or by machine.
Variety advice is deliberately local. Varieties differ greatly in how much cold they will stand and how readily they run to flower, and which one suits a district is a question for a local supplier.
No chemical treatments are named here. The crop is eaten, white rot cannot be treated by a smallholder in any case, and what is permitted differs by country and by buyer.
The netting advice against leek moth and allium leaf miner assumes fine mesh is available and affordable. Where it is not, weekly inspection of the hearts and prompt removal of infested plants is the honest fallback, and it is less effective.

Sources

GBIF Backbone Taxonomy species-match records for Allium ampeloprasum L. and Allium porrum — Global Biodiversity Information Facility (GBIF), Copenhagen (source)
EPPO Global Database — Allium porrum (EPPO code ALLPO) — European and Mediterranean Plant Protection Organization (EPPO), Paris (source)
Allium porrum (leek) and its pests and diseases — CABI Compendium datasheets — CABI, Wallingford (source)
FAO guidance on smallholder vegetable production, nursery raising and post-harvest handling — Food and Agriculture Organization of the United Nations (FAO), Rome (source)

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