Onions are divided into categories: sweet or mild and storage or hot onions. Sweet or mild onions (Vidalia, Maui, Imperial Sweets, Walla Walla) are planted in late fall or very early spring in order to be harvested in early spring to summer. These onions come from warm areas. Sweet onions have much less acidity and will cause you to cry when slicing.
Storage or hot onions (Spanish, Bermuda, boiling onions, pearl) are the most familiar and traditional onions that form the backbone of cooking all over the world. They sting when you bite into them and make you cry because of their strong sulfur compounds.
Onions are high in flavor and nutrients. Along with being low in calories, they also have purported antibacterial qualities. They are a good source of dietary fiber, vitamin B6, folate, potassium and manganese, and a very good source of vitamin C.
Spring onions are a variety of green onion or scallion with a strong flavor. They resemble the green onion, except their white bulbs are larger and more defined. All of the spring onion is edible. They can be used interchangeably with green onions but add a stronger flavor. They can be diced or chopped and added to sauces, stir-fries, and other dishes.