Types of Onions: Colors, Day Length and Allium Vegetables

The types of onions in a market start with one species: Oregon State University Extension describes bulb onions as Allium cepa and sorts them by the day length they need to form bulbs, while Utah State University Extension adds color (red, yellow and white), shape, flavor (sweet or pungent) and market use. Around the bulb onion sit the other allium vegetables: shallots, scallions, leeks, chives and garlic. This guide walks through those onion varieties with extension sources and compares seven raw alliums with USDA FoodData Central values; our onion guide covers the bulb onion on its own.

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Types of onions by color, flavor and use

Utah State University Extension classifies onions by day length first, then by bulb color (red, yellow and white), shape (flat, globe, grano or torpedo), flavor (sweet or pungent) and market use (fresh, storage or processing). The University of Maryland Extension groups them in a similar way, by taste (mild or strong-flavored), color and use, and notes that globe varieties tend to keep longer in storage.

• Yellow and white: Illinois Extension says onion sets are seldom sold under variety names, merely by color, and that most gardeners prefer white sets for growing green onions, although red or yellow sets also work.
• Red and yellow, mild or pungent: Oregon State University Extension says some red and yellow varieties are very mild and sweet in flavor, while others are more pungent because of their higher thiol content, a sulfhydryl compound.
• Sweet onions: an onion with high sugar content may still not taste sweet if its pungency is overbearing, Oregon State University Extension notes, and Illinois Extension says many sweet varieties are very poor keepers that are meant to be eaten fresh soon after harvest.
• Storage onions: Utah State University Extension says most onion varieties grown in Utah are long-day, pungent, storage types.

Short-day, intermediate and long-day onion varieties

Onions start forming bulbs when the day length is right, and different varieties need different day lengths, Illinois Extension explains. Oregon State University Extension gives the ranges: short-day onions typically need under 12 hours of daylight to form bulbs, intermediate-day onions need 12 to 14 hours, and long-day onions need 14 or more hours. The University of Maryland Extension puts the long-day signal at 15 to 16 hours of daylight and the short-day signal at about 12 hours.

• Short-day: these suit southern latitudes, Oregon State University Extension says, and Maryland Extension says they are used in the deep South for winter production.
• Intermediate-day: suited to central latitudes, according to Oregon State University Extension, which says they are planted in the fall and harvested in late spring or early summer.
• Long-day: grown as far north as the northernmost states, Oregon State University Extension says; Illinois Extension adds that long-day types may not get the bulbing signal in the Deep South and that varieties grown in the South are not adaptable to the North and vice versa.

Allium vegetables beyond the bulb onion

The onion family is diverse, Illinois Extension notes, naming chives, scallions, leeks, shallots, garlic and red, yellow and white onions. Extension sources place each of them in the genus Allium.

• Shallots and multiplier onions: the University of Maryland Extension lists both as Allium cepa var. aggregatum, perennial onions that produce a cluster of small bulbs, and Illinois Extension says multiplier onions, sometimes called potato onions, are handled exactly like shallots. Our shallot guide has more.
• Scallions and spring onions: Illinois Extension says true scallions have no bulb, while spring onions have a 1 to 2 inch bulb with green tops, with the smaller bulbs sweet and the larger ones more pungent; it adds that the terms are often used interchangeably. See our guide to green onions.
• Leeks: Wisconsin Horticulture, part of University of Wisconsin-Madison Extension, describes leeks, Allium porrum or Allium ampeloprasum var. porrum, as related to onions and garlic but with flat leaves and relatively little bulb development; the thick leaf bases are eaten as a cooked vegetable. See our leek guide.
• Garlic: Wisconsin Horticulture calls garlic, Allium sativum, a perennial most often grown as an annual, with bulbs made of cloves, and sorts its varieties into hardneck and softneck types; hardneck types produce a woody flower stalk called a scape and softneck types do not, according to Wisconsin Horticulture. Our garlic guide covers it as a food.
• Elephant garlic: Wisconsin Horticulture describes elephant garlic, Allium ampeloprasum var. ampeloprasum, as a leek relative with very large bulbs that is used like garlic.
• Chives: Illinois Extension names chives among the onion family; our chive guide covers the herb.

Onion varieties compared in USDA data

USDA FoodData Central SR Legacy has raw entries for seven allium vegetables. The table lists them per 100 grams so that a bulb and a garnish can be compared, with SR Legacy’s common portion alongside, and ranks them by vitamin C. Each percent Daily Value (%DV) uses the FDA Daily Values for adults and children 4 and older: 28 grams of dietary fiber, 4,700 milligrams of potassium, 90 milligrams of vitamin C, 120 micrograms of vitamin K and 1.7 milligrams of vitamin B6. SR Legacy has no separate raw red, yellow or white bulb onion entry, so the generic onion row stands for all three.

Weight for weight, the leafy alliums lead on vitamin K in USDA data: raw chives list about 212.7 micrograms and raw scallions about 207.0 micrograms per 100 grams, while raw bulb onions list about 0.4 micrograms. Garlic lists the most vitamin B6 of the raw rows, about 1.24 milligrams per 100 grams in USDA data, and the most carbohydrate, about 33.1 grams, against 9.3 grams for raw onions. The portion column changes the picture: USDA weighs a garlic clove at 3 grams and a tablespoon of chopped shallots at 10 grams, while one medium onion weighs 110 grams in USDA data. Our vitamin K foods list ranks more greens.

Raw and boiled onions in USDA data

SR Legacy also lists boiled onions and boiled leeks, drained and without salt, per 100 grams with the same FDA Daily Values, ranked by vitamin C.

Boiled leeks list about 25.4 micrograms of vitamin K per 100 grams in USDA data, against 47.0 for raw leeks, and boiled onions list about 5.2 milligrams of vitamin C per 100 grams in USDA data, against 7.4 for raw onions. USDA values are averages for plain vegetables; fried, pickled or dried onion products differ, and the Nutrition Facts label is the figure for a packaged product.

Pungency, odor and keeping quality

• Why some onions bite: Oregon State University Extension links stronger pungency to a higher thiol content, and Illinois Extension says smaller spring onion bulbs are sweet while larger ones are more pungent.
• Garlic odor: Wisconsin Horticulture says garlic’s volatile oil contains many sulfur-containing compounds that are responsible for its strong odor; our list of sulfur-rich foods covers those compounds across foods.
• Keeping quality: Illinois Extension says many sweet varieties are very poor keepers, while the University of Maryland Extension says globe varieties keep longer and thorough curing increases storage life.

The Dietary Guidelines for Americans, 2020-2025, list onions, leeks, garlic and chives as examples of the other vegetables subgroup. For the leafy side of the vegetable drawer, our guide to types of cabbage covers green, red, savoy and Chinese cabbages, and our list of cruciferous vegetables covers their family.

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Last reviewed October 2026.

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