How to Grow Leeks

Allium porrum

This totally hardy biennial plant is grown in Britain as an annual from seed. It is probably derived from Allium ampeloprasum —which is native around the Mediterranean —and has been cultivated in Europe since the middle ages. We grow leeks for their stem-like structure which is, in fact, a collection of concentrically wrapped, elongated leaves. The familiar white base is produced by drawing up soil around the plants to exclude light. Although the leaf bases are blanched the tops—or ‘flags’— remain green and strap-like.

This vegetable, which has a mild but distinct onion flavour, is particularly useful in the mid to late winter period and may still be available when the last of the stored onion bulbs have been used. By careful choice of cultivars and sowing date, however, it is possible to have leeks available from September until April. The leek is a popular vegetable for exhibition in local shows and competitions particularly in parts of north-east England.

Soil and fertilizer requirements

Since leeks are generally harvested in winter from a summer planting, once again, take care that growth is not so soft and lush that damage occurs in cold weather. The soil should be rich, deep and well-worked in the previous autumn. Maincrop leeks are planted at the end of June or beginning of July so they can follow early peas or salad crops. A base dressing of a well-balanced, general purpose fertilizer such as fish and bone meal should be applied at the rate of 50 to 70g per m2 (2 to 3oz per sq yd) and worked in before planting.

Plant raising

Early, autumn-maturing leeks and those required for exhibition purposes must be raised from sowings made in gentle heat (10°C/50°F) in greenhouses during January or February. Sow the seed thinly into seed trays/pans and when the seedlings are large enough prick them out—either into other seed trays or individual containers—allowing 15 to 20 square cm (6 to 8 sq in) of space per plant. Initially the growth and development is very slow but, following a gradual hardening off before planting, the leeks will be ready to transplant in early May.

Maincrop leeks are sown in an open-ground seedbed as early in March as possible. The seedlings will appear sooner and the plants develop more quickly if you can cover the seedbed with frames/cloches during the early stages. Choose light, well-drained soils for the seedbed and sow the seed thinly in 1 to 1.5-cm (1-in) deep drills which are spaced 20 to 30cm (8 to 12in) apart. The leek plants should eventually be grown at a spacing of 1 to 2cm (about 1in) apart in the rows. The emerging seedlings have a delicate, grass-like appearance and can easily be swamped by weeds. Make sure that the seedbed is hoed regularly but take care not to damage the young leeks. You may need to water the plants to ensure that they are big enough to plant out in late June.

Transplanting and crop management

Leeks can be grown either ‘on the flat’ or in trenches. Remove the young plants from the seedtray/seedbed, having given them a good watering beforehand. Grade the plants for size—keeping the large and small ones separate at planting time—and trim the roots and leaves before planting if they are too long.

It is easier to grow leeks ‘on the flat’ but bigger plants with larger blanched areas are produced if the crop is grown in trenches. In the former method, rows of 15 to 25-cm (6 to 10-in) deep holes are made with a 4 to 6-cm (about 2-in) diameter dibber. The holes should be 20 to 30cm (8 to 12in) apart while a 45-cm (18-in) path is left between rows. Drop one plant in each hole and then fill it with water. This will firm the plants by washing some soil over the roots and prevent birds from pulling the plants out of the holes. During the season the holes gradually fill up and further blanching can be done by-drawing up soil around the plants in late summer and early autumn. Less soil movement is done with ‘on the flat’ growing so make sure that weeds are regularly hoed.

Prepare leek trenches well before planting. They should be 30cm (12in) deep and wide with a 45-cm (18-in) path between them. Heap the soil from the trenches neatly in the pathways. Well rotted organic manure or compost should then be dug into the bottom of each trench. At planting time set the leeks 3cm (1-1/4 in) deep and 20cm (8in) apart in a single row down the middle of each trench. Water them in well and watch for plants which are pulled out by birds—they will need replanting. At monthly intervals through the growing season put soil from the pathways around the plants until, eventually, the trenches are completely filled in. Any additional blanching is then done by earthing up soil around the plants. The plants can be kept clean and soil-free by wrapping them round with a collar of corrugated cardboard before blanching begins.

Harvesting

Leeks are hardy enough to be left in the soil and lifted as needed. If the ground is needed for another crop after February or March, any unused plants can be lifted and heeled in elsewhere in the garden for subsequent use. The crop must be used before May, however, when leeks start to re-grow prior to producing flowers and seed. It is possible to save your own seed from leeks but, as with bulb onions, there are often problems with drying and ripening.

Pests and diseases

Like bulb onions, leeks are attacked by stem eelworm, onion fly, white rot, mildew and grey mould. Leek moth larvae may feed in the centre of the plants during the summer months and cause the leaves to become tattered. This pest is more prevalent in southern districts and the damaged leaves may quickly be attacked by a secondary infection such as botrytis.

Suitable cultivars

Early types (September-November) ‘Early Market’: only for early crops. ‘Lyon-Prizetaker’: well known and popular for exhibition and eating. ‘Marble Pillar’: large, heavy-leeks.

Midseason types (November-January) ‘Musselburgh’: hardy with good length of blanched leaves. ‘Walton Mammoth’: popular and reliable cultivar.

Late types (January onwards) ‘Winter Crop’: dark green foliage; stands until late April. ‘Royal Favourite’: a hardy leek from Royal garden origins. ‘Empire’: one of the best late leeks available.

Vegetables from four plant families are dealt with in this group under the general heading of’roots’. In strictly botanical terms this is inaccurate since turnip, swede and celeriac have swollen parts of the hypocotyl and/or stem included within the familiar storage organ.

These root vegetables are mainly biennials which we grow as annuals. They usually flower in their second year after being subjected to a winter cold period. Occasionally they flower in the first year, however, as a result of being sown too early in the spring, and subsequently being chilled. The so-called roots of some of these crops have a dual-purpose role in cooking as they are eaten either in salads or as a cooked winter vegetable. Beetroot, turnip, carrot and celeriac are in this category. Radishes are most commonly used in salads although there are firm-rooted winter radishes which can be used either raw or cooked. Parsnips, swedes, scorzonera and salsify are usually cooked, although if roots of the latter are left in the ground over winter tender young leaves, which make a palatable salad, are produced in the spring.

All the crops are easy to grow in Britain. Although you can save seed from any of them it is not usual, since cross-pollination with other brassicas is likely to occur with turnip and swede, while drying and ripening can be a problem with the remainder.

28. April 2013 by admin
Categories: Tips and Advice | Comments Off on How to Grow Leeks

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