Answer: To some extent the answer to your question depends on which perennials you want to move. However, in general, they can be moved either in early September or in the spring. If you move them in the fall, be sure to water them well the day before you move them, water them in well when replanted, and keep an eye on the watering until the ground freezes. Also check them during freeze-thaw periods to be sure they haven't "heaved" or popped up out of the ground a bit. (If they do, just scrunch them back in as best you can.)
A container grown rose bush can be planted any time the ground isn't frozen, but spring is probably the least stressfull time for the plant, followed by fall. Bare-root roses are usually shipped in early spring and planted while they are still dormant.
Good luck with your rearranging!
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