The Autumn Joy sedum will die back to the ground level each winter. If they are extremely floppy, you can cut them back to the ground after they die down this fall. Or you can leave the stems until late winter and cut them back at that time. Late winter or early spring is the best time to divide and move them. If they still get too tall and floppy, you can pinch back their growing tips when they're 6 to 12 inches tall to force branching and sturdier growth.