If you've never tasted a sweet onion before, you're in for a revelation. The sweet onion season starts mid-March with big onions from Texas and winds up in August with onions from Washington state and Hawaii.
What makes a sweet onion unique? Its high water content and low sulfur levels. A higher level of water means sweet onions are juicy, but also extremely perishable. Store them in a dry, well-ventilated area in a single layer or in netting or hosiery with a knot separating each onion. When properly stored, sweet onions last two to three weeks at a time. Sulfur gives the common onion its sharp, pungent flavor and causes many a cook to cry. The sweet onion's low sulfur content makes it mild enough to enjoy raw in a salad or sandwich. When cooked, it becomes even sweeter.
Although each variety has its own unique flavor, sweet onions can be used interchangeable in recipes.