Hi! You can still eat spanish onions that have bolted, but in my view I don’t think that they taste quite as good – maybe it has something to do with all the energy used up in producing the flowers
. You should bear in mind that you need to eat bolted onions as you harvest them – they definitely can’t be stored for any length of time.
As a matter of interest, onions are actually biennials that usually go to seed
in their second year. Onion sets have already completed one growing
season and thus will be more sensitive to bolting, so best to buy heat-treated sets where the flowering stalk has been destroyed by high-temperature exposure.