Why are my leeks so thin, and how do I get a long white shank?

Leeks are a long crop. Sown in spring, transplanted early summer, lifted from autumn right through to the following spring — and they build their bulk slowly over that whole period. Almost every complaint about thin leeks comes down to something that shortened or crowded that long run.

Step by step

1. Sow early enough.Leeks want sowing in a seedbed or modules in spring, so they are ready to transplant by early summer. A sowing made in June will grow, but it will never reach size before the light goes in autumn.
2. Transplant at pencil thickness.That is the right stage — big enough to handle and to fill the hole, young enough to grow away fast. Seedlings left in a crowded seedbed until they are thicker have already stopped growing and rarely recover.
3. Trim the roots and leaf tips before planting.Take the roots back to about 2cm and cut the leaf tips back by roughly a third. It sounds brutal; it makes the seedling far easier to drop into the hole and it reduces water loss while it re-roots.
4. Make a deep dibbed hole.A dibber, a thick stick or a trowel handle pushed vertically into worked soil to about 15cm. The depth of that hole is the length of the white shank you will get, because anything the light does not reach stays blanched.
5. Drop the seedling in and do not backfill.Lower it until only the leaf tips show. Leave the hole open around it. Backfilling with soil packs the shank and gives a thin leek — the point of the technique is that the plant has room to expand into the hole.
6. Water in with the rose off the can.Pour water straight into each hole. Enough soil washes off the sides to settle round the roots, and the plant is anchored without the hole being filled.
7. Space for the size you want.About 15cm apart in rows 30cm apart for a standard leek. Widen to 20cm for thick ones. Close spacing gives you slim leeks for early use, which is a legitimate choice, not a failure.
8. Water and feed through summer.Leeks are in the ground through the driest months while they are building bulk. A soak in dry weather and a nitrogen-leaning feed in mid-summer make a visible difference to thickness.
9. Draw soil up in autumn if you want more white.Earthing up around the shanks adds blanched length. Do it gradually and avoid getting soil down into the leaves, which makes them gritty to clean.

Tips

• Leeks stand all winter and can be lifted as needed, which makes them one of the most useful crops on a plot. Lift them before they start to bolt in spring.
• Growing in modules and planting the whole plug into a dibbed hole works nearly as well as bare-root and is easier for small numbers.
• Early varieties are longer and slimmer; late winter-hardy varieties are shorter, thicker and stand the cold far better. Match the variety to when you want to eat them.
• Cut a slit down the length of the shank and rinse under a tap to get rid of grit — earthed-up leeks are always grittier than dibbed ones.
• Do not throw away thin leeks; they are excellent, they just need to go in a soup rather than be braised whole.

Common mistakes

• Backfilling the dibbed hole with soil — It compresses the shank and prevents it expanding, which is exactly the outcome you were trying to avoid.
• Planting seedlings that have grown past pencil thickness in a crowded seedbed — They have already been checked, and a checked leek stays thin all season however well you treat it afterwards.
• Planting too close because the seedlings are small — They look tiny in June and enormous in November. Space for the finished size, not the transplant.
• Letting the row dry out in July and August — That is exactly when a leek is putting on its bulk. A dry summer with no watering gives a thin crop.

Questions people ask