Although onions and other alliums are cheap to buy in the shops and available every day of the year, they are still a hugely important crop for us for several reasons:
We find it hard to source them organically
We like to eat them as fresh as possible (especially salad onions)
We eat them in some form - often several forms - every day of the year
We like to eat more of the plant than is typically available in the shops. For example we love spring onion greens and immature green garlic
They are all extremely healthy and tasty and to some degree the different varieties are interchangable in recipies, so they are a great family for year round growers
We can get varieties that are hard to source in the shops
When growing alliums it's useful to understand a little about certain aspects of their lifecycle, so here's a - very - short introduction!
Onions grow mainly foliage until day length reaches between 14 to 16 hours depending on the variety. Main-crop onions typically start to bulb up when day length reaches 16 hours, which is the middle of May for us, so we want our small onions planted in early April, well rooted and with good foliage growth by then.
The objective with onions is to provide sufficient nitrogen in their early life to feed the leaf growth stage. Ideally most leaf growth will have finished by the time day length reaches 16 hours and the plant will then have enough leaf to be able to support strong bulb growth. Too much nitrogen in summer can lead to bolting (the onion going to seed) or lots of leaf and small bulbs. Lots of leaf growth also leads to thick necks, which reduces storage life (you can still chop them up and freeze them, or eat fresh).
Main-crop onions can be harvested at any stage of their life, as salad onions, pickling onions, small onions or mature onions, but they are typically left to bulb. The benefit of harvesting earlier is that you can also use the onion greens, but most people want the bulbs.
Main-crop onions are mature when their tops start to fall over.
We find it impossible to store our main-crop onions until July/August when our new harvest is ready. There are several options that we use to ensure we never run out: