Onions start bulb formation when the day length is of the proper duration and different varieties of onions require different day lengths to initiate bulbing. In general, most common varieties fall into one of two classes, long-day (for northern latitudes) and short-day (for southern latitudes). For this reason, onion varieties that are grown in the South are not adaptable to the North and vice versa. Late plantings of the suggested varieties also result in small bulbs or lack of bulbing altogether in any location.
High temperatures and low humidity are advantageous during bulbing and curing. Onions have shallow roots and compete poorly with weeds and grasses. Timely shallow hoeing and cultivation are important, especially when the onions are small.
Onions may be eaten raw, broiled, boiled, baked, creamed, steamed, fried, french fried and pickled. They are used in soups and stews and combination with vegetables and meats.
Onions may be grown from seed or very commonly from "sets". Onion sets are produced by sowing seed very thickly one year, resulting in stunted plants which produce very small bulbs. These bulbs are very easy to set out and grow into mature bulbs the following year, but they have the reputation of producing a less durable bulb than onions grown directly from seed and thinned.
Onions are frequently used in school science laboratories because they have particularly large cells which are easily visible even through rather low-end optical microscopes.
Onions are available in fresh, frozen, canned, and dehydrated forms. Onions can be used, usually chopped or sliced, in almost every type of food, including cooked foods and fresh salads, and as a spicy garnish; they are rarely eaten on their own but usually act as accompaniment to the main course.
Depending on the variety, an onion can be sharp and pungent or mild and even sweet.
Chopped, it is one of the three vegetables considered the holy trinity of Louisiana Creole and Cajun cuisine.
Cocktail onions, or pickled pearl onions, are used to garnish drinks.
They appear to be at least somewhat effective against colds, heart disease, diabetes, osteoporosis, and other diseases and contain anti-inflammatory, anticholesterol, anticancer, and antioxidant components such as quercetin.
In many parts of the undeveloped world, onions are used to heal blisters and boils. In the United States, products that contain onion extract (such as "Mederma") are used in the treatment of topical scars.
