A few weeks ago I got excited when I experimented with onion flowers. I cut them and sprinkled them over a garden salad. It was delicious and tasty and I would highly recommend it if your onions flowers. I did a little research however, and found out that unlike garlic, onion flowers are a bad sign. I could paraphrase this, but I think a direct quote will work best.
"Flowering of onions can be caused by several things but usually the most prevalent is temperature fluctuation. An onion is classed as a biennial which means it normally takes 2 years to go from seed to seed. Temperature is the controlling or triggering factor in this process. If an onion plant is exposed to alternating cold and warm temperatures resulting in the onion plant going dormant, resuming growth, going dormant and then resuming growth again, the onion bulbs prematurely flower or bolt. The onion is deceived into believing it has completed two growth cycles or years of growth in its biennial life cycle so it finalizes the cycle by blooming."
Ok, so this doesn't sound so bad. You plan to pick your onion at the end of it's first year anyways. Then I read this.
"What can one do if flower stalks appear? Should the flower stalks be removed from the onion plants? Suit yourself but once the onion plant has bolted, or sent up a flower stalk, there is nothing you can do to eliminate this problem. The onion bulbs will be edible but smaller. Use these onions as soon as possible because the green flower stalk which emerges through the center of the bulb will make storage almost impossible."
Dangit. No more storage or hopes of giant onion bulbs for those plants. Well at least in my case the ones that flowered as a result of our warm then cold then warm again spring were few, and most of my crop is still on track to grow into big beautiful onions. So if yours happen to be in bloom, enjoy the flowers, and then enjoy some green onions!
Quotes were taken from here.