Onions, shallots and leeks are members of the lily family and the genus Allium. Other members of this family are spring onions, chives, Welsh onions, garlic and tree onion.
One of the set questions for this lesson asks about onions, and it is difficult both to provide the answers to the question in the text and to expect you not to be influenced by this in your answer. I would suggest that you consider in your introduction the range of onions grown in gardens, including silverskin onions, spring onions, Japanese and bulb onions as a main crop; then develop your theme with paragraph headings to suit yourself. Inevitably these should encompass such topics as soil, soil cultivation, manures and fertilisers, techniques for raising main crop onions.
Most varieties of leeks are tough, hardy plants which will survive hard frost, and they are therefore a useful winter vegetable. (The very early varieties are less hardy.) When plants grow strongly they produce masses of vigorous whitewhich break up heavy soils. If your soil is heavy and tends to stay in great lumps, try growing a patch of leeks to help improve soil texture.
Earlv Cultivars (Autumn Harvest)
‘Swiss Giant’ ‘Colonna’ High yield, longwith medium dark flag.
High yield, longwith medium green flag.
Mid Season (Jan-March)
‘Autumn Mammoth-snow star
‘Swiss Giant-Albinstar’ High yield, medium long stem, mid-green flag.
High yield, long stem, medium green flag.
Late Season (April-early May)
‘Monument’ ‘Genita High yield, short stem, medium green flag.
High yield, medium stem, green flag.
Site and Soil
Most sites, except those which are heavily shaded, and all well-cultivated soils are suitable. pH 6.5.
Sow early in the year in February/March under cover to get the earliest and largest blanched. An outdoor in March/April will provide adequate crops. Transplant early in May and outdoor-raised in June or even July. Space plants 22.5 cm (9 inch) apart in the row, the rows being 30 – 37.5 cm (12 – 15 inch) apart.
Many growers have developed useful direct drilling techniques which, with a very modest amount of earthing up, if at all, produce heavy cropping with up to 15 cm (6 inch) of blanched white leek base.
Waterwell before transplanting. Use a dibber to make a hole 2.5 cm (1 inch) in diameter and 15 – 20 cm (6 – 8 inch) deep. Drop the young plant into the hole and water it in. Control weeds by hoeing between the rows. Water as frequently as possible; this will give large leeks. When hoeing, draw soil up round the stem a little at a time to lengthen the blanched stem.
Dig up the leeks as you need them from September to April.
PESTS & DISEASES
Pests Description & Control
Leek moth Pale green caterpillar. Feeds inside youngso that only the outer skin remains. Spray with fenitrothion at first sign of attack.
Onion fly Maggots burrow into the base. Lift and burn badly affected plants. Rake bromophos into the soil before
Diseases Description & Control
White rot Foliage turns yellow and wilts. The flesh has a soft whiteand there may be black sclerotia. White rot is a serious and very persistent soil-borne disease. It is worst in dry hot summers. Lift and burn diseased plants. Long rotations help to give some control.
Rust Orange spots and blotches appear on the leaves. Remove and burn diseased plants.
DownyDust when there is dew on the crop with ‘copper/lime dusts.
Neck rot The seed-borne disease attacks the neck of the bulb during storage. Avoid damage to bulbs, particularly during harvesting. Benomyl treated seed minimize infection.
Onion Smut Serious soil borne disease. Dark lead-coloured stripes appear on leaves and bulb scales. Can be reduced by applying formaldehyde sol. down the drill, afterbut before covering the drill.