Answer: When the weather begins cooling and your perennials have slowed their growth you can dig, divide and replant. You don't need to wait for a frost, although with the first frost the tops usually die down which might make handling the plants a bit easier. If you're not a cold weather gardener, you can always wait until spring. Whichever season you choose, be sure to water the newly tranplanted plants after planting to help settle the soil.
Best wishes with your garden!
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