Posted: 29/05/2015 at 11:11
Red onions, I find, are particular susceptible to going to seed (bolting). It usually means the onions have been subject to some sort of stress. Usually lack of water at some time.
Cut off the flower stalk and leave them to continue growing, but use those onions first as they will not store.
As soon as your onions are a usable size, use them straight from the garden. Green leaves and all.