This wonderful vegetable, one of the oldest edible sources known to mankind, found in a bewildering array of recipes and preparations, be it your favorite salad, gravy or curries. It has also been in used in traditional medicines since ancient times for health promoting curative properties. Onions are a cool-season vegetable that can be grown successfully through most of Temperate America. They may be started from seed, sets, or transplants. What starts onions to enlarge is day length. This is in March April. Different varieties of onions require different day lengths. Local garden centers will have the proper varieties for your area. The normally sweet onions that are grown in the south take a longer growing season to turn the starches into sugars.