How to grow Leeks

How to grow Leeks from seed

Leeks may be sown on two separate occasions to provide crops with different uses: in late January to early February for a summer harvest of fresh baby leeks; in spring for sturdy, winter shanks with plenty of earthy flavour. For the earliest crops, sow seeds into trays or pots of multipurpose compost. Space them about 1cm apart and sift over more compost to cover them to a depth of 1cm. Pat the surface of the compost down using the bottom of another pot or a wooden block. Water the tray and place it into an unheated propagator or, alternatively, put a sheet of glass over the top and cover it with newspaper. Keep the seed tray in a greenhouse or cold frame, removing it from the propagator or taking off the glass sheet as soon as germination has occurred. Thin the seedlings to leave about 2cm between plants once they have all emerged.

Sowing outdoors is completed in early to mid-spring as soon as the soil is workable and has warmed up a little – usually late March in the south and April elsewhere. Draw 1cm-deep drills using a garden cane or hoe and then sow thinly. Aim to space the seeds about 1-2cm apart, as most will germinate successfully. Seed should remain viable for up to four years if stored correctly. Space drills about 15cm apart then cover them over using sieved soil. Water thoroughly along the rows with a watering can fitted with a fine rose and keep your seedbed moist at all times. Germination should take around two to three weeks.

Caring for your Leeks plants + problems

Leeks will be ready for transplanting into their final position once they have reached about 22cm tall and are approximately the width of a pencil. For greenhouse or cold-frame-raised leeks, this will be around April and for seedlings started off in a seedbed it is likely to be during late June or July. Be sure to first harden off under-cover-grown leeks by placing the trays of plants outside for increasingly longer spells or by propping up the lights of the cold frame.

Rows of leeks are spaced 40cm apart and the veg placed at 15-23cm within the rows, depending on the ultimate size of leek you desire. Go for the larger spacing if you want decentsized, chunky specimens. Each leek transplant will need preparing by reducing the leaf growth by about a quarter. This limits the amount of water loss from the young plants, helping them to recover from the shock of being uprooted. To plant, make a 15cm hole into the prepared ground using a dibber and drop one young leek into each, ensuring the roots reach the bottom. Next fill each hole to the brim with water and then walk away. As the water drains down it will draw enough fine soil with it to cover the roots and settle it in. The remainder of the hole will naturally fill in as you hoe for weeds or with each rainstorm. This technique increases the amount of white shank that you will achieve.

Shortly after transplanting, your crop may benefit from a liquid feed to give it a boost, although this isn’t necessary on well-prepared, fertile soil. From this point onwards your young plants will need to be watered regularly during dry spells. It is also essential to keep the ground between rows weed-free – being tall, strap-like plants, leeks don’t provide thick ground cover and there will be plenty of opportunity for weeds to gain territory. Do this by hand or use a hoe, but be very careful not to slice the young plants. From mid-August to October the size of the white shank can be increased by earthing up, in much the same way as potatoes. Use a hoe to draw up dry soil against the shank, taking care not to get dirt in-between the leaves as this will lead to a gritty texture when you come to enjoy your leeks. Carry out this technique, also known as blanching, in stages by adding an extra 4- 5cm of soil each time. To reduce the risk of earth tainting the shank you can slip over a tube of material, drawing the soil up around this. The tubing, or collar, could take the form of old piping. Alternatively tie a few layers of brown paper loosely against the shank using string. These collars can be added in stages as the process continues.

During spells of wet weather or in damp conditions, leek rust may attack. As its name suggests, this disease appears as bright-orange, raised fungal pustules, which turn leaves yellow and causes them to die back, while the inner part of the vegetable is generally left unspoiled. When you come to harvesting your crop, be sure to remove and destroy all affected layers, and grow leeks and other alliums on a different site the following year.

How to harvest Leeks

Early sown leeks will be ready for lifting as soon as July, when they can be enjoyed as spring-onion-sized baby veg, leaving others to grow on for enjoying as needed. Leeks sown in spring will be ready from October. Harvest these as they reach the desired size, leaving smaller plants in the ground to increase in girth. The veg will continue to grow in the winter, during any mild spell and will happily sit right through until next spring.

Take great care when you are lifting your leeks and never tug them out with your hands in case they snap. Instead, use a fork to gently rock them back and forth so that the entire plant is extracted in one piece. Leeks are exceptionally hardy and can be left in place all winter, which means they can sometimes get in the way of preparations for new crops. If you need the space, lift any remaining plants and heel them into shallow trenches, placing them on their sides and covering the shanks over with soil, but keeping the leaves clear of the ground. They should store for another month.

Varieties of Leeks

Leeks varieties to try