No, they don't need plant food at this stage - the leaves of larger alliums such as aflatuense and christophii are rather floppy in their habit, so that's normal, but turning brown isn't - if you have them in pots, and it sounds like you do, perhaps you missed watering them when they needed it a while back. Assuming your pots have drainage holes, and they're not standing in trays which hold water, then any excess water should drain away, so difficult to over water.

no they dont particularly need feeding but in my experience some lose the leaves before the flower forms. They look very forlorn just before the flowers come. This could be the cause.

I have mine in the garden soil. Are they in large pots?

snap bamboo :)

Thanks all. Yes forlorn's the right word. Their leaves look droopy, good to know thats not necessarily a bad thing. They're not in pots but are in a raised bed. Hope they're not deseased. One of them has a yellowy/brown colour on the tips of the leaves. Should I treat it, or pull it out? Will it spread?
RD

No, this is perfectly natural. The flowers form as the leaves are dying off and by the time the flowers open the leaves are often completely dead. At the shows they cut the dead leaves away just leaving the flower stem.

My alliums tend to grow too crowded and the roots don't get enough nutrients or water. Every two or three years I divide them rather roughly, and air and enrich the compost. They seem to need that. Plenty of sun, besides.