Late September or October make sure you prepare the planting hole with good humus rich material when you plant and be prepared to water well until winter settles in and they die back.

You could split the hostas up into smaller plants as well, Gillian, then you'd have even more! Just use 2 garden forks to prise the bits apart, making sure you have some root with each bit, and then plant them as MG says, and they'll romp away. Give them plenty of water when you re-plant them. Good luck....Annie