White onion or Allium cepa (“sweet onion”) are a cultivar of dry onion which have a distinct light and mild flavour profile. Much like red onions, they have a high sugar and low sulphur content, and thus have a relatively short shelf life.^[1] White onions are used in a variety of dishes, such as those of Mexican and European origin. Their uses in dishes often relate to their mild nature, they are often included in dishes to provide a light, fresh and sour taste to dishes and are often added uncooked to dishes such as salads.^[2]

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White onion
White onions
Genus	Allium
Species	Allium cepa

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White onions have a distinctively mild flavour palette in comparison to other onion cultivars such as the red and yellow onions. They are distinctly less pungent and have a lighter flavour on account of their relatively high sugar and low sulphur content than other onion types. Because of this mild and easily palatable flavour, white onions are often used raw in dishes such as sandwiches and salads. When raw white onion is soaked after being finely chopped, it adopts a relatively sweet flavour profile as it loses its astringency.^[3]

Due to this flavour profile, white onion is versatile in its uses for food. Its use is oftentimes central to the construction of salads as it provides a fresh, but not overwhelmingly pungent flavour sensation. It is also widely used as a central ingredient in the making of stews as its light flavour does not overpower the other elements of the dish, contributing to a cohesive flavour palette. White onion is also extremely useful as a component in fermented dishes such as coleslaw as its low astringency allows it to adopt a largely sweet flavour in the dish. It also has many uses in dishes such as salsas because of this low astringency.^[4][5][6]

There are multiple methods of planting white onions:

• Onion Transplants: a method by which seedlings started in the current growing period are bought and planted in one's own garden. This method often yields quick bulb growth, but the plants are more vulnerable to disease in maturity.^[22][23]
• Onion Sets: small bulbs from the previous harvest are not allowed to mature and are dried. These bulbs are used in the current season, and often grow the quickest out of all planting methods and produce larger than natural bulbs.^[22][24]
• Onion Seeds: seeds of the white onion that can be planted into sets in late Spring. While this method may have the longest grow time (up to 4 months for mature bulbs), the onions produced are the least susceptible to disease.^[25][26][22]

Different varieties of onions vary in the time of year at which a mature white onion is cultivated:

• Short-day onions are onions that form bulbs when they are in an environment where they get 10 to 12 hours of sunlight a day.^[27][28][22]
• Intermediate day onions are onions that will form mature bulbs when they are in an environment where they get 12 to 14 hours of sunlight a day.^[27][29][22]
• Long-day onions are onions that form bulbs when they are in an environment where they get 14 to 16 hours of sunlight a day.^[27][30][22]

For most white onion varieties, a soil pH of 6-7 is optimal. At times when the pH of the soil for onions is below 5.5, magnesium and molybdenum supply is inadequate and at a pH of above 6.5, zinc, manganese and iron are less present in the soil.^[31]