Onions can be grown from seed, sets or modules (4 seed in each plug). Seed offers the least resistance to competing weeds, but are cheaper to establish. The crop is kept clean from weeds mechanically, with a variety of machines. Bulbs start to swell around the longest day and the leaves begin to die back. The bulbs are lifted and dropped back on the floor during a hot spell to cure the skins. the onions are then lifted again a stored. The neck of the onions need to be dried to stop diseases spreading during storage.