I let mine mature after breaking the flower stem off, but then I use those ones first, and I don't try to keep/store them (although I suppose they could be frozen)
This happens to many early planted onions. Dai's right, nip off the flowers - try and nip them off as early as possible (when they are small buds preferably) as the plant wil put all its energy into producing flowers rather than into the bulb. Dispose of the nipped off buds carefully, because onion fly are attracted to the scent of the cut onion plant.
I imagine that when planting onions you would do the exact opposite to when you plant out daff bulbs. With onions you are attempting to force them to grow blind ( hence the leaving the nose just proud of the soil) ???? IS this right, or am I way off?
Onion is a biennial - so would normally flower & set seed in the second year, but some "bolt" in the first year (normally because they are stressed in some way, or perhaps genetically unstable)
I think the bolting problem is much worse with sets, because sets are in their second year of growth, and like Kristen says they are naturally trying to flower. I recall that sets are sometimes sold as 'conditioned' so as not to bolt - I'm not sure how that works. In the last couple of years I've delayed planting my onion sets until March/April and had much fewer problems with bolting.
Interesting. I had a look in Hessayon: Sets more inclined to bolt than from-seed Modern varieties much less prone to bolting. Sets which are no larger than 3/4" across are less likely to bolt. Perhaps I should try growing them from seed ... Seeds more prone to disease and Onion fly (and sets better for poor soil, which mine will continue to be for another couple of years until the Compost and Manure treatment long term benefits kick in) Joy Larkcom says "Optimum set size 3/4" circumference"
Just to ask an additional question then-why do we plant them with their nose showing-I know about the ridge receiving maximium sunlight therefore warmer soil.
