I would keep them in pots till they beef up, something like a gallon pot and once roots are poking out of the drainage holes it would probably be safe to get them in the ground. Several years ago I got several little band roses and potted them into gallon pots. After about 6 weeks most had doubled in size and were ready for the garden. I think you'll want to get them in the ground by early fall so they have time to establish before cold weather sets in. I think some soluble fertilizer is a good idea; I'm giving my potted rose a dose of half strength all purpose fertilizer weekly. Or just some slow release like Osmocote would be good. I think mulch would be a good idea, but they should survive the winter.
