Several of my onions are forming flower heads. Why?
Onions are grown from seeds, sets, and plants. Flowering is most likely to occur on onions grown from sets. Sets are small onion bulbs that were grown the previous year, harvested, stored through winter, then distributed to garden centers in early spring. When purchasing sets, select bulbs that are smaller than a nickel in diameter. Sets larger than a nickel in diameter are much more likely to flower. Flowering plants are best used as green onions as they do not form good-sized bulbs.