How to Grow Onions
It is best to grow onions from “sets” (immature bulbs) as opposed to seeds.
Plant them in September / October for Autumn plantings or March for Spring plantings.
When planting onion sets, ensure the root plate is at the bottom and they are planted vertically. Plant so that the tip is at the soil surface. Leave 5-10cm between sets and 30cm between rows.
Keep the onions free of weeds and they will benefit from being fed with a nitrogen fertiliser (this can be found in any garden centre or ask your Goody Goody Gardener) every few weeks.
They are fairly hardy but you can cover them during cold winter weather.
June / July for Autumn sown sets.
July / August for Spring sown sets.
Once the bulbs are mature, the foliage starts to turn yellow and fall over. When this begins, gently fork the onions out of the soil to avoid damaging the root plate. Leave them on the surface to dry. In a few weeks they will have “cured,” this means the skins have gone papery and they can be stored.
If it's unlikely to be dry enough to allow this, then store them somewhere cool and dark, where air can freely circulate to achieve the same effect.