Sow seed in a pot or tray of seed compost. The seeds are small, but try and space them about 1cm apart. Lightly cover with a thin layer of compost then stand pot or tray in water to moisten.
When the seedlings are a few inches tall, prick them out and transplant into fresh compost. Once established, transplant seedlings into the garden, 10-15cm apart.
Alternatively, in spring, plant heat-treated onion sets, into soil that has had large stones and weeds removed, and been enriched with organic matter. Plant each set 10-15cm apart, with tip protruding. Water newly planted sets and cover immediately with horticultural fleece, to prevent birds from lifting them. Once firmly rooted, the developing crops can be uncovered.
Using a watering can with a rose, thoroughly water seedlings and sets directly after planting to settle soil around roots or bulbs. Repeat at regular intervals if the weather is dry.
Hoe regularly to remove weeds, which will compete for water and nutrients with developing bulbs. A hand-held 'onion hoe' or 'circle hoe' are both perfect for weeding in small spaces.
In late summer, draw away earth from the bulbs to expose them to the sun. Harvest after the leaves turn yellow and the stem bends over. Allow leaves to dry before carefully lifting bulbs.