There are several different types of onions, most all of which are used to enhance the flavor of food when cooking. The different types of fresh onions are mostly recognized by their color. Onions are divided into two main categories – green and dry. Dry onions are further categorized as either spring/summer onions or fall/winter. The spring/summer varieties are sweet onions and the fall/winter varieties are for storage.

Green onions are onions that are harvested while their shoots are still young and green. Green onions are chopped and used for toppings on salads, baked potatoes, soup, and a wide variety of other culinary uses. The green onion and the scallion are typically used interchangeably both in reference to the onion itself and in cooking, but they are actually two different varieties of green onions.

Dry onions can be red, white, or yellow in color. They are harvested once the shoots have died and the onions are left with a paper-like covering encasing the fleshy vegetable. Spring/summer onions are the sweeter varieties, but do not store well like fall/winter varieties. The most common variety of sweet onion is the Vidalia onion, which is named for their growing location in Georgia. Other sweet onions include the Sweet Imperial, the Spring Sweet, and the Walla Walla, named for its growing location in Washington.

Storage onions such as the red onion, the boiling onion, the shallot, and the Spanish onion are found in stores year round, but are at their prime in late fall. Storage onions are most often yellow, though they can come in all three common dry onion colors. They have a longer shelf life than spring onions and contain less sugar and water. This makes them ideal for flavoring dishes that require long simmering or cooking times such as chili or roasting meats.

In addition to flavoring many dishes, onions are also prepared pickled, boiled, sauteed, and deep-fried. Deep-fried onions prepared as rings or petals are a popular appetizer in many American restaurants. Besides fresh onions, onions can also be purchased canned, frozen, and dehydrated as a spice or powdered.

When selecting fresh onions in the store, look for onions that are firm and dry with a shiny, crackling outer skin. Be aware of excessively strong odors as this might indicate rotting. Rather, fresh whole onions should have a mild odor. Also avoid onions with dark spots as this can indicate mold. Sweet onions are best used fresh because they do not keep well. To get the best flavor out of sweet onions, purchase and use them within a day or two.