At a glance
Leeks occupy a unique position in the kitchen garden. Unlike most vegetables that peak in summer and are done by autumn, leeks come into their own from September onwards and can be harvested right through until April if you choose the right varieties. They fill the winter hungry gap – the months when almost nothing else is cropping – with a vegetable that is genuinely useful in the kitchen and requires minimal effort to maintain once established. They are also exceptionally hardy, standing through hard frosts that would destroy most other crops without any protection needed.
Growing leeks well comes down to two things: starting them early enough to produce transplants of a good size, and planting them out using the dibbing method that produces the long, blanched white stems that make leeks worth growing. Neither of these is difficult, but skipping either step produces disappointing results. This guide covers the full process from seed to harvest.
Choosing a variety
Leek varieties are divided into three groups by harvest season – early, maincrop and late – and choosing across all three gives a harvest window that runs from August all the way through to April without any gaps. Early varieties are thinner-stemmed and less hardy; late varieties are the most cold-resistant and can stand through the hardest UK winters without deteriorating.
Musselburgh is the most widely grown variety in UK gardens for good reason – it is easy, productive and tolerant of difficult conditions. For a longer season, sow one early variety alongside a late variety and you will have leeks available from late summer through to spring. Avoid mixing all your sowing into one variety unless you can process large quantities at once, as leeks left in the ground too long in spring will bolt and become unusable.
Sowing from seed
Leeks are started indoors because they have a long growing season – typically six months from seed to harvest – and an early indoor start gives them the head start they need to produce plants of a useful size by transplanting time. Sow from January in a heated propagator or from February onwards on a warm windowsill. Fill small pots or module trays with fine seed compost and sow seeds thinly, 1cm deep. Cover with a thin layer of compost and water gently. Germination takes 14-21 days at 15-18°C.
Once seedlings emerge, grow them on in good light to prevent them becoming drawn and weak. A windowsill in a cool but frost-free room is better than a warm dark position. The seedlings look like thin grass blades as they develop – this is normal. When they reach pencil thickness (roughly 20cm tall) they are ready to transplant, which is usually from May through July depending on when they were sown. Before transplanting, harden off the seedlings by placing them outside during the day for a week or two.
Transplanting and planting out
The dibbing method is the traditional and most effective way to plant leeks. It produces long white stems by dropping the plant into a deep hole and allowing the hole to fill gradually with water and soil rather than firming it in by hand. The result is a much longer blanched section than if the plant were simply inserted into a shallow hole and earthed around.
Prepare the bed
Dig the bed over and remove any large stones or clods. Leeks do not need a rich soil – avoid freshly manured ground as this can cause forked roots. A bed that has had compost dug in the previous autumn is ideal. Rake to a fine tilth.
Make the holes
Use a dibber to make holes 15-20cm deep and 15cm apart, with 30cm between rows. The holes should be just wide enough to drop the seedling in without forcing. For a standard row, mark a line with a cane and space holes evenly along it.
Trim and drop in the seedlings
Trim the roots to about 2cm and trim the leaf tips by a third to reduce moisture loss. Drop one seedling into each hole so that roughly 5cm of the white stem section sits above ground. Do not firm the soil around the plant.
Water in to settle the soil
Pour water gently into each hole. The water washes just enough soil around the roots to hold the plant without compacting the hole. The soil settles gradually over the following days and weeks as rain falls. This is what produces the long blanched stem – the plant pushes upward through loose soil rather than being buried from the start.
Earthing up and ongoing care
As leeks grow through summer and autumn, earth up around the stems every few weeks by drawing soil from between the rows up around the developing plant. This extends the blanched white section and improves the quality and length of the usable stem. Each time you earth up, take the soil no higher than the base of the lowest leaf – burying the leaf joints encourages rot. Three or four earthing-up sessions through the growing season are usually enough to produce a good-length white stem by harvest time.
Leeks need very little watering once established in a normal UK summer – rainfall is generally sufficient. In dry spells, a good soak once a week is better than frequent shallow watering. Feeding is not usually necessary if the soil was well prepared. Weed between rows regularly, particularly in the early stages before the plants are large enough to shade out competition. Once leeks are established they are largely self-sufficient and need minimal intervention beyond weeding and earthing up.
Use a collar to produce even longer white stems. A length of drainpipe, a cut-down plastic bottle or purpose-made leek collars placed around each plant as it grows will extend the blanched section further than earthing up alone can achieve. This is mainly worthwhile for exhibition growing or if you particularly value very long white stems, but it adds no extra work once the collars are in place.
Harvesting
Leeks are harvested as needed rather than all at once – they can stand in the ground for weeks or months and will not deteriorate if left. Lift with a fork rather than pulling, as the roots grip the soil firmly and pulling often snaps the stem. Push the fork in alongside the plant, loosen the soil and lift. Trim the roots and outer damaged leaves before use.
Early varieties are best harvested before the worst of winter as they are less tolerant of hard frost. Maincrop varieties can stand through winter and be harvested as needed. Late varieties are the most resilient and can be left until April, by which time other spring vegetables are beginning to come through to replace them. Once a leek begins to produce a flower stalk in spring – visible as a thickening at the base of the plant – harvest it promptly as the stem will become tough and inedible once bolting begins.
Common problems
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