Onions keep best when stored in cool, dark places—sparrowgrass thinks the fridge works just fine. "Don't store potatoes and onions in the same place," sparrowgrass warns. "One causes the other to sprout and spoil."
Sweet onions (including Vidalias) that haven't been cured for dry storage can be individually wrapped in paper towels and stacked in the crisper, says Karl S—they keep for months that way.
Discuss: Storing onions and garlic
Sweet onion image from Shutterstock