Floppy onion leaves, not yet mature

I've noticed that a number of the leaves on my onions (Red Baron, from sets) seem to be very 'floppy'. They're aren't lying over and yellowing like they would if they were mature, just odd leaves are falling over and lying almost along the ground. They're not yellowing, and there is no other obvious sign of distress I can see. A few have 'broken' and I've snapped these off, but many more are just very soft and can't stand up under their own weight.

Ideas? I have been watering them quite heavily (using up the rest of the watering can after keeping newly planted seeds moist). They're in a raised bed, with quite heavy clay soil.

One thought I had was too much nitrogen, but the only fertilsing I've done is a relatively small dose of Growmore on teh top of the soil before I planted them. Maybe it's just the wind? I don't know.


Cheers.