Since I re-planted a lot of
abandoned onions from last year, it's no surprise that most of them have sent up a flower stalk. Once an onion has sent up a flower, unfortunately it won't store very well. The stalk grows into the bulb and will decay after it is harvested, making the bulb rot from the inside out. That doesn't mean the onion is a lost cause, of course - let them continue to grow; once harvested, you just need to use them up first. I plan to make a lot of salsa and French onion soup with mine!
Still, I like to snip onion flowers off early, as I have with the ones in the picture here. Advice varies on whether doing this helps the onion itself grow larger. In theory, if the onion no longer has a flower, it should focus on growth rather reproduction. Don't know if that is true in practice.
My main reason for cutting off the flowers, though, is that the onion flowers are edible! It doesn't hurt the rest of the plant, and the stalks can be chopped and used for anything that otherwise calls for green onions or chives. You can also snack on them raw; mine are sweet and mild at first but have a bit of heat after a minute or two.
Alternatively, you can leave the flowers and let them bloom in the garden, as I did last year. They are round balls of white flowers - small but pretty. Their brethren, ornamental alliums, have larger, showy clusters that are striking in flower gardens (violet ones are pretty popular at the moment). The onion flower in full bloom is still edible, so it can be snipped off and used as a garnish or in a salad.
