For bumper crops you will need to improve the growing area by digging in plenty of compost or well-rotted manure in the autumn.
Leeks are best suited for growing in the open ground, but you could grow several in large, deep containers or raised beds. They are not suitable for growbags.
Leeks can be either sown directly in the ground outside, or in seed trays (and left outdoors). If you only want a few leeks, it is best to sow in seed trays, then transplant outdoors. Use modular trays and sow one seed per module.
Traditionally, leeks are sown into a seedbed, which is a site away from your main vegetable plot and transplanted later in the season. This is because sowing leeks at their final spacings in your main vegetable plot would take up a lot of room early in the growing season, when you could be growing fast-maturing crops such as lettuce.
Sow seed thinly 13mm (1/2in) deep in rows 15cm (6in) apart in a seedbed in March and April.
Leeks are ready to transplant in June when they are about 20cm (8in) high and the thickness of a pencil. Water well the day before lifting and transplanting. Prepare the plants by trimming off the root tips.
Make 15cm (6in) deep holes, 15cm (6in) apart in rows 30cm (12in) apart and drop a plant into each hole. Fill the hole with water to settle the roots. You don’t need to backfill the hole with soil, just let the water settle the soil around the roots. If you have a lot of plants, try dropping two or three into each planting hole. You'll get smaller leeks but the overall yield should be the same.
To increase the length of white stem it can be blanched by gently drawing up dry soil around the stem in stages, but try not to allow soil to fall between the leaves.
Water during long, dry spells and weed regularly.
Start lifting when the leeks are still quite small to ensure a long harvest period. Gently lift from the soil using a fork.
Leeks can remain in the ground through the winter until they are needed.
‘Carlton’ AGM: This is a top choice with seed that germinates and grows quickly. The stems are ready to harvest September to November.
‘Pancho’ AGM: An early maturing cultivar with long, crisp white stems and good rust resistance.
‘Apollo’ AGM: A mid-season cultivar, ready to harvest in about December with blue-green leaves and good rust resistance.
‘Toledo’ AGM: This leek produces long stems with dark blue leaves and is a late season cultivar, ready to harvest late November to late February.
Leek Rust: This is a fungal disease causing bright yellow spots on the leaves. It is often worse in long, wet spells.
Remedy: Mild attacks of rust won’t affect the plant, but serious infections may cause leaves to shrivel and affect yield. There is no control for rust once you have the infection. Make sure you don’t crowd plants, as this increases humidity and increases the likelihood of infection. Dispose of any badly affected plant material, and don’t grow garlic, leeks or onions in the same spot for three years.
Read more information on leek rust
Onion white rot: This fungus causes the leaves to wilt and turn yellow. Under wet conditions, the plants may not wilt but will become loose in the soil. If you lift the plants, you will see a white fluffy growth on the base.
Remedy: Throw out any infected plants, and don’t grow onions, garlic or leeks in that spot again for at least eight years. This is a very persistent fungus that survives in the soil for a long time. There is no chemical control.
Read more information on onion white rot
Leek moth: This is a relatively new pest of leeks and onions and thought to be mainly concentrated around the south-east coast of the UK, although it has been found further inland and north. Caterpillars tunnel into the leaves, causing whitish-brown patches to develop on leaves. In severe cases, leaves may turn yellow and rotting occurs within them.
Remedy: Once you see the damage, there is nothing you can do to control it. Remove and destroy infected plants. When planting out, cover leeks with horticultural fleece (like Enviromesh) to prevent adult moths from laying eggs.
Read more information on leek moth