When can peonies be separated and transplanted?
Peonies can be kind of fussy about where they’ll grow and what they’ll do if you try to move them. In fact, most garden experts will tell you that peonies seldom need dividing, and recover poorly from any attempt to do so.
That said, there’s a good time to do if, if you must, and that time is late summer or early fall. Make divisions or root cuttings with at least three growing points, then replant the divisions 18 to 24 inches apart. Plant them in a new bed that has been dug 12 inches deep, into which you have worked good compost or other organic matter. Pick a spot in full sun or a place that gets a little afternoon shade. Set plants in the ground at the same level or slightly higher than they were growing before you dug them up.
The cuttings should begin to grow next spring, so make sure they have sufficient moisture when they do. Judy Lowe, the author of Month-By-Month Gardening in Tennessee & Kentucky, suggests placing a half-inch of compost on top of the soil in spring and summer, and applying a slow-release fertilizer in mid-spring.
Then sit back and be patient. Even with this good care, it may take a couple of years for a transplanted peony to recover and bloom well again.