You can buy onions in bulbs called sets in bags from the garden centres. They can be planted in Autumn or Spring and harvested 6 months later.
Before planting onions you’ll need to prepare the site.
1) Loosen the soil with the fork and remove any weeds or large stones. Onions should be planted in sunny or partially shaded sites, protected from the wind. Do not plant them in a heavy clay soils. If you have poor soil, you may want to add organic matter before you start planting onions. Use your feet to form down the soil as onions grow well in a hard soil. Slightly loose soil after that.
2) Choose your onions. They should not be soft or too small.
3) Make small halls in a soil. Halls should be as deep as an onion bulb and leave the top exposed.
4) Gently firm down the soil around the tip with your fingers. The tips should be planted about 10 cm (4in) apart from each other.
5) If you plant your onions during the Autumn, then don’t water them unless the soil is very dry. You can harvest onions by late spring.