Onions come in an impressive array of sizes, colors, and shapes. Their botanical name is Allium cepa, and they are easily crossbred. Growers are continually developing new varieties and hybrids. The common medium-sized yellow globe onions, which are available year round, encompass many different varieties, with subtle differences in taste or texture. The globe shape is popular with consumers, so growers have emphasized it.
Whatever names are bestowed upon onions, though, they fall into two general categories: storage onions and spring/summer onions. Storage onions and scallions can be found year round, but sweet onions are in greatest supply from late spring through the summer.
Note: The shallot resembles both the onion and garlic. The shallot bulb is wrapped in a delicate, onion-like coppery skin, and it is divided into small, segmented cloves like garlic. However, unlike garlic, the cloves are not enclosed by a sheath and as a result are easier to separate. Shallots can be found in both yellow and red varieties.
These have firm flesh, dry, crackly outer skins, and pungent flavors. Grown in northern areas of the United States, they are harvested in late summer and early fall. After a brief period of drying out—a process known as “curing”—they are stored for several months. In stores, these onions may simply be labeled by color—yellow, red, or white. There are no nutritional differences among these types.
- Bermuda onions: Imported from Bermuda, this large storage onion is sweet and mildly flavored. Bermuda onions have mostly been displaced by various sweet onion varieties grown within the US. The name is sometimes used generically to refer to sweet onions, though technically this is wrong, as sweet onions are not storage onions like the Bermuda.
- Boiling onions: These are very small onions that are picked when they are 1 to 1 ½ inches in diameter. They can be red, white, or yellow, though in supermarkets they are usually white.
- Cipolline onions: These squat, disk-shaped onions were originally from Italy but are now being grown in the United States. They are bittersweet and tender and can be used like pearl onions. They can be yellow or red.
- Pearl onions: These are actually pearl-shaped bulbs from a number of different onion varieties. They are so densely planted that they attain a size of only an inch or less in diameter. While pearl onions were once only available as white onions, they are now available in white, gold, and dark red or purple varieties.
- Red (globe) onions: A somewhat sweet type of storage onion, these are good in salads and lend color to sandwiches.
- Spanish onions: These are a variety of very large storage onion, distinguished by their mild flavor; the skin color can range from yellow to purple.
- Sweet onions: Sweet onions are shipped almost immediately after harvesting and so are not considered storage onions. There are many varieties, including the Vidalia, the Walla Walla, the Sweetie Sweet, the Maui, the Mattamuskeet Sweet, and the Pecos.
- White onions: Most often sold as small boiling onions, there are also large versions of these onions. Their skin is thinner and more papery than other onion types, and they tend to spoil a little more easily.
- Yellow (globe) onions: These are storage onions and come in a variety of sizes. They are the most common onions on the market and the type that most people think of when they think of onions.
The category of spring/summer onions includes so-called “sweet” onions as well as members of the onion family that are sold in the early shoot stage, such as scallions and green onions.
Spring/summer onions are shipped almost immediately after harvesting. All of the “sweet” onions have a very high water and sugar content, which means that they spoil more quickly and will not hold up as well as storage onions do. Sweet onions are quite juicy and in some cases mild enough to be eaten raw.
Sweet onions are grown primarily from fall to spring in warm-weather states, such as Texas, Georgia, Arizona, and Hawaii. Some are designated by names referring to their growing areas, such as Vidalia, Walla Walla, Maui, Mattamuskeet Sweet, and Pecos. Others are known by their varietal name, such as Granex and Grano. One, the Texas 1015, was named after its optimal planting date of October 15. Some sweet onions have a flattened shape, but many look just like storage onions.
- AmeriSweet onion: These large, round, globed-shaped sweet onions have a thick, deeply colored skin.
- Green onions: This term is used by most people interchangeably with scallions, but there is actually a minor technical difference. Strictly speaking, scallions are bulb less, while green onions are harvested at the miniature bulb stage. But from a consumer’s viewpoint, the two types are nearly identical.
- Imperial sweet onions: These onions hail from California’s Imperial Valley.
- Italian bottle onions: Developed in the Calabria region of Italy, these red-skinned, bottle-shaped “heirloom” onions are sometimes sold as torpedo onions or red torpedo onions.
- Maui sweet onions: Grown in volcanic soil in Hawaii, and first introduced on the mainland by tourists returning from vacation, the Mauis are sweet and make good slicing onions.
- Oso sweet onions: These come from South America and are said to contain 50 percent more sugar than Vidalias.
- Scallions: Though they look like skinny leeks (an onion relative), scallions are true onions—just very immature ones. Scallions are pulled from the ground while their tops are still green and before a significant bulb has formed. In some countries, such as China, scallions are the most popular form of onion, and they are often eaten as a vegetable in their own right.
- Spring onions: In addition to being a category of onion, this is also a market term for green onions. They are very small onion bulbs with their green tops on.
- Texas 1015 onions: A type of Grano, this onion can grow to softball-size. It was specifically bred—by a team of horticulturists lead by Leonard Pike at Texas A & M University—to not make people cry. Its nickname is the “million-dollar baby,” because of the money spent to develop it.
- Vidalia onion: Perhaps the best known of the sweet onions, these are grown in 20 counties in Georgia. Although you can often identify these onions by their distinctive shape (somewhat flat on the stem end and rounded on the bottom), you will find that Vidalias and many of the other specialty sweet onions are stamped with a label telling you just what they are.
- Walla Walla onion: These large, round, sweet onions are named for the city in Washington where they are grown. In order to claim the name Walla Walla, they must be grown within a specific area in the Walla Walla valley.