Onions are a member of the allium family, which includes salad onions, over-wintered onions, main-crop onions, leeks and garlic. This guide focuses on main-crop onions, which provide a fresh harvest in late July/August and can be stored until about May, they can also be pickled or frozen to extend the season further.
I have a comprehensive guide to growing alliums for a year round harvest, which complements this guide.
I use a rating system to help me decide what to grow and it considers lots of factors, but the main ones are: how tasty it is, how healthy it is to eat, how expensive it is to buy, how big its harvest is, when its harvest period is and whether I can buy it organically and if not how much pesticide commercial growers use.
Main crop onions are near the top of the ratings, spring onions even higher because they can be harvested fresh year round. However onions score well in a few categories:
They are however:
If you are used to buying onions from the supermarket then you will have been eating small/medium sized bulbs and these typically grow at a density of 70/m2. Onions are harvested in August and typically keep until at least March, so 8 months. So find out how many onions you eat each month and multiply that by 8 and divide that by 70 and that’s how many m2 you will need.
However if you don’t have a lot of space, that can work out to be a lot of space, dedicated to a fairly low value crop, which you might not be able to store. In which case I’d recommend that you grow salad onions, which are a much more valuable crop that can just be harvested fresh from the ground all year round.
Like almost everyone we eat onions all year round, in fact we eat them every day of the year. This can present a bit of a challenge because stored onions usually start to rot or sprout in spring and your main-crop onions won't be ready until late July.