Although it is the most cultivated species of its genus, no one knows the origins of domestic onion, Allium cepa. Leek, shallot, garlic, chive, and a few other species are also popular vegetables. Most common bulbing onions produce familiar distended bulbs that are ready for harvest after defoliating and initiating dormancy in autumn. Green onions are leaves and attached juvenile bulbs.
Onions are probably easiest to grow locally from small juvenile onions known as ‘sets’, that grew from seed during the previous summer. Alternatively, seed sown during summer grows into small plants that go dormant to overwinter, and then resume growth the following spring. Mature onions should go completely dormant in autumn before storage, but are usable directly from the garden.
Yellow or brown onions are the most popular for cooking. Red or purple onions are milder and more colorful for fresh use, and are also popular for stir fry. White onions, whether fresh or cooked, are even milder, and are the traditional onions for salsa. All onions produce distinctively bluish foliage that stands about a foot high. The hollow leaves flop over and shrivel for dormancy in autumn.