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Onions can be one of the easiest vegetables to grow, or one of the most difficult. It all depends on how they are grown and whether they are just for the table or prize specimens for a show. It is a vegetable that is very responsive to good soil and cultivation, but will give a worthwhile crop in very average garden soil too.


The easy way is to grow from sets. It might be regarded as cheating by serious onion growers, but for many it is the only way of getting success. To grow from seed successfully does mean getting the seed in, in good time. Late sowing doesn't produce a later crop, just smaller onions. Onions from seed are usually of better quality though. There is also a much greater choice of varieties including some excellent modern F1 hybrids.


Soil preparation can go to great lengths for onions. It is often advised by some onion growers that it is best to grow onions on the same onion bed every year, and therefore build up the nutrients and soil conditions ideal for onions. This is unwize practice. Onions are prone to a number of pests and diseases and being included into a 4 year rotation is important to minimize build up of such problems. That old advice comes from the days when gardeners were happy to use large amounts of chemicals, most of which will have been banned by now anyway (those which are most effective usually).


Heavy manuring and liming (if needed) is required by onions. Do not do this at the same time or toxic ammonia gas will be released. If both have to be done in the same season, then the lime should be applied first. Lime in the Autumn, leave it to wash in for at least 3 months and then dig and apply manure. Although onions are a surface growing bulb (they are NOT root crops, even though they are often refered to as such) the roots do go deep and searching. Double digging and manuring of both the top soil and the subsoil is beneficial. By double digging correctly, the subsoil will not get mixed with the top soil.


A high pH of 6.8 to 7.2 is ideal and balanced towards high Nitrogen. Apply fertilizer according to recommendation if soil testing has been carried out. If not apply a compound fertilizer in the proportions of NPK 3.1.1 (parts by percentage with multiples of - such as 27.9.9) High magnesium is required and can be applied either as Dolomite Lime or Magnesium Sulphate (epson salts).


If growing by seed, the sowings can begin in a heated greenhouse with bottom heat in late January or during February, or a cold greenhouse from late February. Sow thinly into seed trays of multi purpose compost and then prick out at the early stage, before the seedling opens up and straightens (known as the crooked stage). It is vital that the seedlings are not pricked out deeper than they were in the original seed tray. The bulb area must stay near to the surface or a bulb will not develop properly later on. It will grow with a thick neck and be useless for storing. Pricking out can be in soil less multi purpose compost or John Innes No1. Small pots or modules can be used instead of trays for the pricking out.


Sowing in situ under cloches, or into cold frames can be done in March, and this is the best approach for ordinary kitchen onions. Sow thinly into drills 2cm deep and 30cm apart. Thin out to 8 to 10 cm apart. Hoe regularly down the rows and hand weed around the plants. Onion foliage cannot smother weeds at all, because of the needle shape, so therefore onion beds need frequent weeding.


Top dress or liquid feed regularly with a high Nitrogen feed until about mid July. After this time the ripening process will begin, so there is no advantage in feeding from then on. The tops begin to fall in early August and by early September the onions are ready for harvesting and storing.


Onion sets achieve decent onions from an April planting. They have a head start and seed sown in April will never catch up. Seed sown that late will not make decent onions in time. The long wispy tops of the sets should be trimmed back before planting into drills 3cm deep. The sets should be just covered, but no deeper. The practice of pushing sets into loose soil is only for the type of gardener who do things the easy way, not the correct way. Pushing them in means as soon as growth begins, the roots push the bulb up and out of the ground, due to the hard pan created under the bulb. The birds then get the blame.


Sets generally do not produce such a hard onion and are not so storable. Some are heat treated to help prevent premature bolting, and this does seem to work. Bolting onions from sets are not such a problem when heat treated .


Spring onions and pickling onions are sown thinly in drills 25cm apart and not thinned out. These can both be sown outdoors from April to July. Pull spring onions while young and lift picking onions in September after the top have died down. A poorer soil suits pickling onions as this makes them smaller and harder and with a stronger flavour.









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