Best time is in winter while dormant and the ground is workable. Late winter. Have new hole ready or pot them up. Take as much as the roots as you can. You may want to cutdown top side to match roots left behind. Keep well watered if you put in pot, or after you put in new hole. It's going to suffer a bit, but should be OK, I don't know much about the species you have some plants do better than others.