|Sowing to harvesting||Bulb||14-23 weeks|
|Size||Bulb||5-10cm (2-4") diameter 50cm (20") high|
|Spring||1cm (1/3") diameter 20cm (9") high|
|Yield||Bulb||20 bulbs @ 125g (4oz) per 3m (10') row|
|Spring||60 onions per 90cm (3') row|
Growing Onions and other Alliums
The onion is one of the most underrated vegetables, mainly because shop bought varieties tend to be bland at best and they have become almost a commodity.
They belong to the allium family, which also includes leeks, garlic, chives and a number of ornatmental flowers as well.
They are biennial plants which we grow as annuals with the exception of onion sets,(see below), which are in fact bulbs that are ready for their second year of growth and which the seed producers stoped growing early in their first year. When grown from seed their natural cycle is to germinate from a seed into a plant and then into a dormant bulb for the rest of the year then the following spring they begin to grow again and produce a flower spike.
When growing your own, you can choose to grow for your own tastes instead of having to settle for the rather bland conformity of those bought in the shops. How strong a flavour the onion has depends on the sulphur content, the more sulphur the stronger the flavour. Like all plants onions require potash to grow, and it is the amount of potash available that determines the amount of sulphur absorbed, the more potash the less sulphur. So a low amount of potash will result in smaller but stronger flavoured onions.
Another way of regulating the size of the onion is the spacing between the plants, the close together they are the smaller they will be.
Plant Sets or Sow Seed? Which is best?
Main bulb onions (white or red varieties) are either grown from seeds or sets, which are effectively small bulbs.
Spring onions or scallions (green onions), which are all the same just different names, are nearly always grown from seed.
While starting from seed is not difficult, it is often better for beginners to start of with sets, if using bulb varieties. This is because the sets have a head start so they start growing more quickly, they are more disease resistant, in general they will crop better in poorer soils and will usually provide a crop even if they go in later than they should.
On the other hand growing onions from seed has the following advantages, the seeds are cheaper to buy than the sets and are avialable in far greater number of varieties. Also those grown from seed are far less prone to bolting (i.e. going to seed before they are ready to be harvested) and in the main seem to store better. Also when starting off from seed you can do so in a container indoors and give the seeds an early start and protection from the elements (useful in areas further away from the equator)
Japanese onions are grown to over-winter and should really be grown from sets, they do not however store very well but do fill a gap between the end of those in store and the start of the next crop.
Shallots are practically always grown from sets. You can get seed but it's very unusual, in fact a recent search on the internet of seed providers turned up no results for shallot seeds. Cultivation is very similar to onion sets except they like a little longer in the ground. Shallots, apart from the flavour difference (i.e. being considered sweeter and milder), has the advantage of being able to be kept in storage for longer. They are also almost exclusively used in the making of home made pickled onions