Allotments 4 All

I planted four varieties of onion jet set/ Hercules/ centurion / sturon and up to last week all have been doing fine .
now even though we have had some rain and i watered in between the leaves are falling over already and they are not as big as they should be!
do you think they need some form of feed or is it the hot weather that's causing them not get bigger and starting to fall over??

It may be the hot weather causing them to fall over early, but once they get to that point feeding won't make any difference.