what's wrong with my caulie's?

This is my first year of having an allotment and everything has been going well except when it comes to my cauliflowers. They either develope little hearts and seem to be doing fine, then when they get to about 2 or 3 ins across they start going to seed, some have not developed hearts at all. I've grown them at home in the garden before and not had this problem. Can anyone tell me what's wrong?

Thanks mumofstig, I thought it was something I'd done wrong, or not done!

I know I did that (and I know DD does ) so just having firmed soil doesn't always give you good caulis... I wish it were that easy 

I'm jealous, the biggest of mine was 3inches across 

  There is that...but I wouldn't pay through the nose

This is my first year of having an allotment and everything has been going well except when it comes to my cauliflowers. They either develope little hearts and seem to be doing fine, then when they get to about 2 or 3 ins across they start going to seed, some have not developed hearts at all. I've grown them at home in the garden before and not had this problem. Can anyone tell me what's wrong?

Mine did this too 

DD said it was lack of water at the crucial time 

I have also had great caulis. they are massive and very tasty, as are all my brassicas. I grow them in raised beds prepared as follows:-
Horse manure put on in October 2010.
6 x fertilizer put on in February.
Sulphate of ammonia in March.
Sowed seeds (candid charm) February in seed compost with added John Innes.
Planted out in April.
I don`t know if this is the correct way of doing this but it worked for me this year.  Last year was my first year on allotment and had dreadful Brassicas.