Why do keep getting Onion failure?

Are you growing from sets? or seed? I prefer sets because you get a head start just bury them with their heads just sticking through - watch blackbirds though they seem to think they are worms!

I may be wrong, but i thought that onions don't need much fetiliser/manure. I grow my red/white onions and shallots in beds that have not been improved in the current year. I also used to leave the heads protruding, as Geniusscuffy says, but had the problem of birds pulling them out. then I read that sets will be just as successful if the bulbs are just completely submerged below soil level so that the birds can't find them so easily. I did so this year, and had no problems with the outcome.

It may not exactly answer your question but I always start my onion sets off in trays then plant them in position when the roots have just started growing. By doing this the birds are not able to pull them out.