September onwards for daffodils and October onwards for Tulips.

Agree if you are buying new but if you have them in pots after a display this spring you could plant them now and let them die back naturally. I tend to do this as I can see where the ones are in the ground and where suitable spaces are.

I never ' lift ' my Daffs & Tulips . I know where they are in the garden & they always come up every year . Beautifully