Apparently, onions may originally have come from Central Asia, and are one of the oldest cultivated vegetables. They were revered in Ancient Egypt some 5000 years ago, where they were considered to symbolize eternal life.
Health benefits. Perhaps we should revere them as well for their known therapeutic effect of lowering cholesterol, cancer and blood pressure levels. Also contain vitamin C . As the health benefits are lowered by heat, eating raw onions in salads will give the maximum benefit.
There are many different varieties of Onions available. The colour can be red, golden or white. The shape may be round or like a torpedo. The red and white coloured ones tend to be milder and sweeter, while the golden ones tend to store better.
Some onions, like the Japanese onions, can be over-wintered to provide an earlier crop the following year especially if grown in a mild area of the UK, or with protection elsewhere. Other varieties produce a small, white onion for pickling, while others are grown as salad onions or sybies. Salad onions are naturally small and will not grow into large onions, however long they are left to grow.
Onions can be grown either from seed or sets. Sets are small immature onions, from 1 to 2 cm diameter, whose growth has been suspended in the Autumn until they are planted again in the following Spring. Specially heat treated sets are less likely to bolt, or go to seed. The heat treatment for some 20 weeks, apparently extends the growth period, thus increasing yield. Heat treated sets may not be available till March or April. Growing from sets seems to be the easy usual way of growing Onions.
Growing Onions from sets.
For standard onions, the sets should be planted in the Spring in well drained ground, and not newly manured. The sets should be planted just level with the soil surface, at 10 cm centres, with rows 30 cm apart. To prevent Birds pulling out the sets, cover with netting.
Suggested varieties of standard onion sets.
Red Baron. This is an early, strong flavoured, good storage onion with flattish bulbs and a red skin.
Hyred. Red skins but smaller than red baron.
Centurion. Early, golden brown onions.
Forum. Early, light golden brown onions.
Fen Red. Slow to mature and very red.
Red Arrow. Another good red onion.
Suggested varieties of Japanese or over wintering onion sets.
Senshyu. Slightly flattened, brown skinned bulbs, maturing in late June.
Electric. A good flavoured red onion.
Growing Onions from seeds.
For standard Onions, the seeds need to be sown in January or February to give the seedlings the longest possible growing season. Because of the cold, snow, frost and rain at that time of year, you may get a crop failure, except perhaps in the mildest part of the country with the use of cloches.
It is therefore usual to sow the onion seed in cells in gentle heat in January. Transfer the tray of cells to a cool greenhouse or cold frame in March to harden off the seedlings.
In April during a period of mild weather, plant out the seedlings, still in their plugs of compost, at 10 cm centres, with rows 30 cm apart.
Growing from seeds means that it is not possible to bring in any diseases, or nematodes.
Suggested varieties of Onion Seed for standard Onions.
Red Baron. Red globes with good flavour and storage.
Long Red Florence. Mild flavoured long red bulbs. Can be pulled young for salads.
Autumn Gold. A golden brown globe.
For Japanese over wintering Onions, the seed should be sown thinly in situ in July or August in drills 1 cm deep, with rows 30 cm apart. In the North of the UK, some cloche protection over the coldest, wettest Winter months would be helpful. In the Spring, when you can see how many of the seedlings have survived, you can thin them out to about 10 cm apart. Eat any thinnings as salad onions.
Suggested varieties of Onion Seed for Japanese over wintering Onions.
Senshyu Yellow. Claimed to be reliable with good flavour. Harvest in 10 to 11 months.
For Salad and Pickling Onions, which are only grown from seed, sow the seed thinly in situ in March or April, in drills 1 cm deep with rows 25 cm apart. Cloche protection can be useful to ensure good germination of the seed. Harvest as required when they are big enough.
Suggested varieties of Onion Seed for Salad onions.
White Lisbon. A popular, quick growing, white skinned variety.
North Holland Blood Red. A red skinned mild flavoured variety.
White Lisbon Winter Hardy. Should survive the Winter to crop in the Spring.
Suggested varieties of Onion Seed for Pickling Onions.
Purplette. A purple skinned variety.
Paris Silverskin. Produces crisp small cream bulbs, which can be eaten raw in salads.
General Onion cultivation.
Sometimes onions plants will form a flower stalk and this should be removed as soon as possible. Sadly, such Onions will not seal properly or keep well, and therefore these Onions should be used first.
Do not water Onions in dry spells after May, as it may encourage white rot.
Onions are sensitive to the day length and foliage growth stops after the longest day in June. However, the bulbs will continue to grow while conditions are favourable.
Lift the Onions in June or July, when the leaves have started to turn yellow or brown. Let them finish off drying in a well ventilated, sunny, covered place, such as a cold frame or greenhouse. Nowadays, it is not recommended to bend the Onion tops over to touch the ground, in case disease enters.
Storage of the Onions should only be carried out when really dry. Rub off any loose skin or remains of roots and foliage. Store in mesh bags in a cool, frost free, dry place. Inspect your stored Onions regularly for any signs of mould and remove any infected bulbs.
Pests and diseases.
Onion fly maggots burrow into the base of the bulbs and cause drooping and yellowing of the leaves. Remove and burn affected Onions.
White rot is caused by a fungus and is indicated by the presence of a white, fluffy mould on the base of the bulbs. Remove and burn affected plants. Unfortunately, the fungus stays in the ground for a long time and alliums should not be grown in the same ground for up to 8 years. Strict rotation of crops and not over-watering, helps to minimise this problem. See here for a further description of white rot and a possible treatment.
Reproducing onions by bulbils, “pips or grass”. This is the method by which super specimens such as “show onions” are usually grown. These show onions are specially selected strains to produce giant onions. You can see the principal of this method if you allow one of your onions plants to form a flower head in the second year( they are bi-annuals), or if they have gone to seed in the first year. Give them the following treatment, and instead of forming onion seed pods, they will form green shoots which can be planted up. It is not what you would expect to happen, but nature is very complex and surprising! Onions produced by this method will be genetically the same as the original plant.
Allow the flower buds to form and then using small scissors, cut off all the individual buds. The onion plant then compensates for this treatment, by trying to reproduce itself by forming bulbils, pips or grass, as shown in the photo.