Growing onions from sets
You can plant onion and shallot sets in early spring or autumn; from an autumn planting, you’ll get earlier, heavier crops. Both like sun and a moisture-retentive, fertile soil, ideally with plenty of well-rotted organic matter such as garden compost.
It's worth looking for heat-treated sets, as the resulting plants are less prone to bolting (producing flowers). Bolting reduces the quality of the crop.
Rake over the soil to break down any large lumps. Plant the sets with the tips showing. Onions need room to swell, so space them 10-15cm apart, allowing 30cm between rows.
Cover with fleece or netting so birds can't pull them up.
Tending the crop
Drooping yellow foliage is the first sign of onion fly larvae, but by then they'll already be eating their way through the bulb. You can protect crops by growing them under fleece.
Onion-neck rot can be a problem in wet summers. Telltale signs are brown marks and fluffy grey mould. Don't overcrowd when planting, and dry bulbs thoroughly before storing.