Onions are usually biennials--they go to seed in the 2nd year. If the bulb overwinters fine, the following year it puts up a seed stalk and flowers. Usually a white or pink globe, perhaps 2'' round, made of tiny flowers that form black seeds when busted open.

You can also try growing sets and then replanting the largest sets, as they often go to seed more than the smallest sets.

I think what happens to the bulb depends on the variety/type. Multiplying & potato onions divide or multiply and rarely send up flower stalks. Egyptian or "walking onions" form bulbils up at the top of the plant, hence the term "topset" but I don't think they ever really "flower, per se. Some divide or multiply below ground but biggest reproduction is when the topset bulbils fall over to the ground and root and become plants. Standard onions that send up a flower stalk the onion bulb in the ground pretty much becomes useless for food--the center "eye" is green--it's the flower stalk. Some green onions multiply/divide. Some onion types like shallots can be perpetuated--they divide& multiply and form leaves, but if left in the ground will flower the following year and go to seed. The seeds fall and germinate and the whole process starts over again, growing bulbs, dividing/multiplying, growing leaves, overwintering, flowering, going to seed, etc, so what start out as, say, a few shallots, unharvested, can turn into a whole patch of hundreds a couple years later!

Hope this helps.

Mark

Thanks. Will it seed if I plant a bulb, or would it be better if I bought seeds?