Get the most from LEEKS
Choose these tasty, reliable alliums for crops you can harvest for months. Helen Billiald explains what to do
Everyone likes a bit of certainty in this topsy-turvy world and leeks offer reliability in spades. These are unobtrusive banker crops, growing quietly in the background until winter arrives and you suddenly notice them in all their resilient glory.
Sweeter and milder than onions, you can harvest them for eight months of the year if you choose cultivars carefully. Early-season leeks grow quickly and offer long stems from August to late autumn but won’t stand up to frosts. Mid-season leeks are harvested from autumn to mid-winter and are a bit more cold hardy, while late-season leeks crop from early winter right through to the following April, happily unfazed by sub-zero temperatures.
Leeks like good living on fertile soil with plenty of moisture in sun or part shade. Adding compost or well-rotted manure to your soil helps improve its structure and ensures it can hold on to moisture even at drier times of year. If space is limited, grow leeks in large containers; just make sure they’re deep enough to allow planting into pre-dibbed holes for long white stems.
The growing cycle of leeks is a long one. You can start seed under cover in February, or sow direct outside into a seed bed in March and April, planting them in their final positions from May to early July. If you’re keen on the longest season of harvest, pick an early cultivar to sow in February for late summer leeks, and sow your maincrop in a seedbed a month later.
How to sow them
Sow seed 1cm (½in) deep in a tray of multipurpose potting compost. Sow thinly across the tray or use modules with two seeds per compartment, thinning to one if both germinate. Keep the trays in an unheated greenhouse or coldframe unless there’s a cold snap, in which case bring them into a cool room of the house to germinate (10-15C/5059F is ideal) then move back to the greenhouse to grow on.
For direct sowing, prepare a fine seedbed once the ground has begun to warm in March or April (look for the telltale sign of germinating weed seedlings). Sow thinly 1cm (½in) deep, spacing each row 15cm (6in) apart and taking care to label them. Once they’ve germinated, thin to 5cm (2in) apart.
Leek seedlings go out to their final position when they’re pencil thickness and at least 20cm (8in) tall, usually when they’re around 10 weeks old. If you only want a small number of leeks you can often pick up a tray of seedlings at your local garden centre in early summer.
Leeks sown outdoors in a seed bed can be left
until they’ve grown large enough to transplant to their final growing positions. However, those sown early under cover in a seed tray can exhaust the available nutrients before they’re large enough to plant out. Therefore it’s worth transplanting the growing seedlings into modules or lining them out in a deep seed tray. Or, begin supplementary feeding to ensure they don’t become stressed from a lack of nutrients.
When it’s time to plant out in their final growing positions, transplant only the largest, healthiest seedlings. To attain a lovely long white shaft, you need to blanch them as they grow by making 15-20cm (6-8in) deep holes and planting the leeks directly into the hole. The below-ground part of the leek will be white and milder in flavour. You can use a specialist dibber to make these holes, but there’s usually something to hand that can be adapted to the task, whether a metal spike or broken spade handle. Water the bed thoroughly the day before you plant or you’ll find dry soil falls back into dibbed holes as quickly as you make them (see step by step overleaf). Keep your leek bed weed free with regular hoeing and by mulching between rows. Water deeply during dry spells to make sure they don’t go short of moisture.
Those who are committed to growing the longest white stems can plant them along the bottom of a trench, then backfill the trench as the plants grow, earthing them up. Try to move the leaves out of the way as you backfill the trench to minimise soil falling among the leaves.
Plant spacing varies depending on when you want to start harvesting. Should you be after young leeks as well as more mature ones, space them at 15cm (6in) intervals and harvest alternate plants, leaving every other plant to grow on and fill out the space. If you’re only after large winter leeks, plant at 25-30cm (10-12in) spacing from the outset and they’ll fill out beautifully.
Choose cultivars carefully and you can harvest leeks for eight months of the year