Growing your own leeks provides a versatile vegetable that is easy to grow and is ready in winter and early spring when other vegetables are scarce and expensive.
They are a member of the onion family and are very tolerant of soil conditions growing almost anywhere provided that the soil is not waterlogged.
Generally speaking there are very few pest and diseases that affect them, the more common are listed at the bottom of this page.
Choosing a site.
Although leeks are tolerant of most soils conditions they grow best on a light moist but firm soil. Soil that has been freshly manured is not suitable for them, as this will produce plants that are tough and course with too much leaf growth. Apart from this remember that the leeks will be in the ground until required throughout the winter and so can remain in the ground for over a year. Do not grow leeks on the same ground year after year, as this will increase the risk of pest and diseases
Sowing your leek seeds.
If you want summer and autumn leeks then you need to sow under glass in winter. If you want them in winter / spring then sow either outdoors in mid spring or indoors if you prefer.
Sowing outdoors can follow two paths; one sow where they are going to grow permanently, two sow in a seed bed and transplant. If sown in the permanent position the space is taken up for a very long time before harvesting. This has to be balanced against the additional trouble of having to transplant. There is no right or wrong way and the choice will be governed by your individual requirements.
Sow the leeks in finely raked soil in drills ½ cm deep (¼″), and if in permanent bed 15cm (6″) apart. As germination is usually high sow the seeds thinly, and cover lightly with fine soil. After covering the seeds firm the down the soil and water. The leeks will germinate in 2 to 3 weeks. After six weeks start thinning out to about 1 plant every inch or so, then later to 10 cm (4″) apart. Then again, if in the permanent bed to 15-23 cm (6 – 8″) apart, this is done in mid-summer.
Once the leeks are 20cm (8″) tall and about the thickness of a pencil it is time to transplant to the permanent bed. At this point you can buy young leek plants from the nursery hence saving the bother of sowing and thinning. Try to transplant when the soil is moist otherwise water the seed bed well the day before.
There are several methods of planting out, the one described here is the most common for leeks grown for kitchen use. Using a dibber (or trowel) make vertical holes about 15 cm (6″) deep. The holes should be slightly wider at the top than the bottom and should be 5 cm (2″) in diameter. Trim the roots until they are 2 ½ cm (1″) long and slightly trim the leaves. Lower the young leeks into the hole and gently fill with water. As you are planting you will be able to tell which way the leaves are arching, it is a good idea to plant so that the leaves all arch along the row.
Cultivation and care.
Until they are well established they need to be watered regularly. Then whenever there is a dry spell. Regularly hoe between the rows, this keeps the weeds down and gradually fills the holes with loose soil. Leaves that grow too long may be cut back to avoid them tailing on the ground and starting to decay.
To increase the amount of the leek that is edible it is necessary to blanch the plants which also improves the flavour. This is a gradual process and is done in several stages. Generally it is started in mid–autumn. It is done by pushing up the soil around the leeks to a depth of 5cm (2″), you may protect the stems by putting paper collars round the plants up to the bottom leaves.
Depending on the time of sowing Leeks may be harvested from mid autumn to the end of spring. They should be levered out of the ground with a spade. If you remove the largest first the smaller ones will put on some size over the next few weeks.
Pests and diseases
Onion fly will occasionally attack leeks with most of the trouble caused by the larvae tunnelling into the leeks, infected leeks should be lifted and destroyed.
Leek Moth is a small brown moth which lays its eggs at the base of the leek in spring. Again the most trouble occurs when the green caterpillars tunnel into the leeks leaving white streaks in the leaves.
Allium Leaf Miner is a relatively new pest in the UK but is prevalent on continental Europe. Currently there are no chemical controls known to work on this pest. The best way to prevent this pest attacking your leeks is to cover them in enviromesh. Please see the Defra website for more details.