When growing onions, it is often advantageous to use onion sets rather than grow from seeds. Onion sets are immature bulbs specially grown to be planted, they tend to be easier to grow, less prone to bolting and more resistant to diseases and pests.
Soil Preparation
Dig in some manure or good quality compost the winter before you plan to grow onions, this gives it time to break down and improve the soil.
Planting Onion Sets
I always plant my onions in early April, but you may get away with doing it earlier depending on your location. Plant the bulbs 4 or 5 inches apart with rows spaced 8 to 9 inches apart. Push each bulb firmly into the soil with the tip still showing.
Birds will sometime pull your newly planted bulbs up, if this happens just push them back into the soil. You could also cover them with some garden netting for a few weeks until they start to develop leaves.
Weeding
Keep your onion patch weed free. No one enjoys weeding but keeping on top of the weeds will allow your onions to grow bigger.
Harvesting
Harvest onions once the stems/leaves have turned brown and fallen over. You should leave the harvested bulbs outdoors to dry out which should take a just over a week, weather depending of course.
Store dried onions in onion nets or on stackable trays in a cool dark place. Use larger onions first and discard any soft onions. Onions that are properly dried and stored will keep for up to 9 months.