How to grow leeks

When many gardeners think vegetables they tend to think runner beans, lettuce and peas - crops that all give you a glut as they need using up quickly, however winter crops mature and stay in the ground for several months. 

They can be lifted every week, effectively becoming an outdoor larder, and they crop when prices are highest.

Leeks are one of the winter staples and these members of the onion family are the hardiest crop of all. However cold winter is, they can be relied upon to survive.

They can be boiled and eaten in white or cheese sauce, or made into soup along with potatoes. If a dish requires onion, leeks can easily be substituted in quiches and casseroles etc. Plus, they are easy to grow and look handsome for months.

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When to plant

Seeds

Leek seeds can be sown under glass between February and March because this hardy vegetable germinates in cool conditions.

Once the seedlings are up you don’t have to worry about cold nights. However they are shallow-rooted, like all alliums, so they cannot seek out moisture from the depths. 

Seedlings

Transplanting the seedlings outside usually takes place in the second half of May, although they can be planted out up until mid-July at a push, as most of the growing takes place in autumn.

Where to plant

Seedlings can dry out easily and they can bolt (or run to seed) later if they become water-stressed. So it’s vital to keep your seedlings damp and out of direct sunlight in the greenhouse.

Leek seeds can be also be sown outside into the ground in a drill but not until mid-March at the earliest.

Find out about the best winter vegetables to grow

How to plant 

Seeds

The easiest way to raise leeks of the right size under glass is to use 6x4 modules. Fill each space with seed compost and then place two seeds in each one. 

F1 varieties are better germinators and faster growers. Weed out the weaker seedling and leave the other to fill the space. Water with seaweed extract once the seedlings are three inches high - this toughens up the foliage and feeds the plant.

Planting outside

Leeks do not do well on compacted soil, so adding some well-rotted organic matter really helps this crop dramatically. This should be done the autumn before you plant.

Once the young plants are pencil thick (after ten weeks or so) they are ready to go outside. However, even slender leeks (ones that haven’t thickened up enough) should be in the ground by late June, if at all possible.

Once they are ready to plant outside, make a deep hole with a dibber and drop one leek plant in each and then fill the hole with water - a technique known as puddling in. Forking over the soil a day or two before planting makes it easier to get the dibber in.

Make sure each hole is at least six inches deep (15 cm) with nine to twelve inches between each (22 - 30 cm) as the part beneath the soil gets blanched to white and stays tender. This is the most useful part for the cook.

Rows should be between twelve and fifteen inches (30 - 38 cm). Wider spacings help air flow and prevent diseases like rust.

Once the seedlings have been ‘puddled in’, water the whole plot well and keep it damp. Don’t dribble on water, use a sprinkler if possible. Give the whole area a thorough soaking for at least two hours in the latter half of the day.

Caring for leeks

The tops and roots of leeks do not need trimming - this is an old wives’ tale.

Whenever dry weather occurs in the first month after planting it is important to give them a thorough soaking, not a sprinkling, in the latter half of the day. Once they look established leave them to their own devices.

Keep the weeds down – remember leeks have shallow roots.

If a leek bolts, snap off the stem.

You can earth them up to blanch more stem and some gardeners grow them in a trench and gradually fill it in.

When to pick

Leeks can be left in the ground over winter, the cool conditions acting as an outdoor larder. Lift as you need them, using a fork, as they are best eaten very fresh. Leeks will not store.

Try Mary Berry's recipe for leek and potato soup

Best varieties of leeks

Choose a good F1 variety  - the seeds germinate better. Avoid the old varieties like Musselburgh - they are full of cellulose and tough to eat and to digest. 

‘Oarsman’ AGM

A smooth-skinned, maincrop F1 hybrid leek that’s much kinder on the stomach than the thickly-textured, cellulose-packed ‘Musselburgh’. Long, sleek shanks that cook sweetly.

‘Carlton’ AGM

An earlier F1 variety producing mid to dark-green flags, but ‘Carlton’ bolts more easily than some - so not for dry gardens.

‘King Richard’ AGM

An early variety producing pale-green leeks - resists bolting well.

‘Apollo’ AGM

Vigorous plants with attractive dark green leaves that fan out from a thick white shank. Ready from mid-late winter and resistant to rust.

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