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How to Grow Leeks


Leeks belong to the onion and garlic family and they are a great vegetable to grow in cooler climates.

Compact, versatile and easy to grow in various soil conditions, they’re a fundamental cornerstone of any vegetable patch.

Tasty and succulent to eat, leek foliage is also prized as an ornamental feature of borders, or round the edge of your allotment.

Click here for Leek Troubles

Sowing Time Planting Time Soil Spacing Cutting / Lifting Time Storage Cooking
Leeks are the easiest member of the onion family to grow and they will withstand the hardest of winters. They tend to be pest and disease free and don’t need a very fertile soil.
Sow outdoors in spring when the soil is warm, mid March onwards. For April crop sow late varieties in June. Germination takes 14-18 days. It will take 30 weeks to maturity or 45 for late varieties. Transplant seedlings in June when they are about 8ins high. Water well before moving, trim roots and leaves. Make a 6ins deep hole, drop in the leek and fill with water and wait for it to settle. Don’t back-fill with soil. Transplant late varieties in July. Choose a sunny site. Any reasonable soil will do. Dig over well during the winter and add compost or well-rotted manure every other year. Level and firm the soil and add a general fertiliser a week before planting. Set in rows 12ins apart and 6ins between plants. Keep weeds down and water well during dry weather. Draw soil up and around the stems once they are well developed. Increase the height a little at a time. Stop earthing up in October. Stop feeding late August. Begin lifting when leeks are quite small to extend the harvesting period. Lift gently with a fork to avoid damage. Leeks can remain in the ground throughout winter and used as needed. If required, leeks will keep in a poly bag in a fridge for up to 5 days. To freeze: Remove the green tops, wash stems and cut into small chunks. Blanch for 3 minutes, cool, drain and dry before packing into poly bags. To cook: Wash thoroughly to remove any grit. Boil in a small amount of water for 10 minutes.



Leek Troubles

Trouble Symptoms Treatment Prevention
Onion Fly Yellow, drooping leaves. Maggots burrow into the bases and kill young plants. None. Lift and burn affected plants. Rake Chlorophos into soil before showing or planting. Sets are less prone than seeds.
Bolting Premature production of flower-heads. Cut off flower stalks and lift as usual. Do not store. Don’t sow or plant too early in the season. Ensure soil is firmed well before sowing or planting
Stem & Bulb Eelworm Swollen, distorted foliage. Young plants die and older plants product soft bulbs. None. Lift and burn affected plants. Do not grow onions, peas, beans or strawberries on land previous infected with this disease.
Saddleback On harvesting, bulbs are split at the base. Caused by heavy rain or watering after a dry period. None. Use affected bulbs immediately. Keep well watered during dry spells.
Set Division Onions from sets produce twin bulbs. None Plant sets in good soil and keep well watered in dry spells.
Smut Black spots and blotches on leaves and bulbs of young plants. Twisted and thickened leaves. More likely in leeks than onions. None. Lift and burn affected plants. Don’t grow leeks or onions on affected ground for eight years.
Rust Orange spots and blotches on surface of leaves. More likely in leeks than onions. Remove and burn affected leaves. Don’t grow leeks or onions on affected ground for one season.
White Tip Tips of leek leaves turn white and papery in autumn. Spray with Dithane at first signs. Lift and burn badly affected plants. Don’t grow leeks or onions on affected ground for one season.
Bull Next (Thick Neck) Abnormally thick necks means the bulbs will not store successfully. None Don’t use too much manure. Use a feed with more potash than nitrogen. Don’t sow seed too deeply.
Downy Mildew Downy, grey mould covering leaves. Leave die back slowly and shrivel. Bulbs are soft and don’t store well. Spray with Dithane at first signs. Repeat fortnightly. Grow onions on a difference site each year and ensure soil is well drained.
Leek Moth Tunnelled leaves. Caterpillars feed inside young leaves leaving the outer skin. Also attacks leeks. Spray with a contact insecticide at first signs of attack. Destroy badly affected leaves. None
White Rot (Mouldy Nose) Foliage turns yellow and wilts. Fluffy white mould on base of bulbs and round black bodies appear in the fungus. None. Lift and burn affected plants. None. Don’t grow onions on affected land for eight years.
Shanking The centre leaves turn yellow and collapse, outer leaves follow later. Evil-smelling slime within scales. None. Lift and burn affected plants. None. Don’t grow onions on affected land for several years.
Neck Rot During storage a grey mould appears near the neck. Bulbs are soft and rotten. None. Remove rotten bulbs. Dist seeds and sets with benomyl before planting. Dry bulbs thoroughly before storing. Don’t store soft bulbs or bulbs with green necks.