Dividing Mother's Peonies
Q: Our mother passed away recently and I’d like to divide her old peonies to move to my and my siblings’ gardens. Can we divide them in the fall?
A: I know how plants like this become treasured family heirlooms that can virtually live on forever. In our family, we all have divisions of a Japanese Fernleaf Peony and starts of an old Christmas cactus that have been passed along. I’m sorry you’ve lost your Mom.
Yes, you can divide these in the fall. I often start dividing Peony and Bearded Iris as early as July. You wouldn’t think that the heat of summer would be the best time but it works well and gives the roots time to establish before the next spring. Dividing them later in fall is fine too.
When digging peony (especially very large, old plants), loosen the soil to a spade’s depth all the way around the plant and remove it like a moat. Once the surrounding soil is removed dig deeper and inward, into the roots. Often the roots are well over a foot deep making it nearly impossible to get them all. Cut through the roots trying to retain at least 8 or 9 inches of the thickest parts. Once the root ball is out of the ground, you can divide it. In the late summer and fall, you will already see plump red buds at the top of the roots that will be next years’ growth and flowers. Using sharp pruners, divide the roots by cutting through them, leaving as many of the new buds on each piece as you wish. The bigger the division the faster the new plant will establish. Keep in mind that you need at least one bud per root for it to survive.
Keep the roots and root divisions dark and moist until they can be re-sited or potted. Usually, I’ll place them in a box or large pot and cover them with moist garden soil or fine mulch until planted.
Planting depth is very important. Try to set the division so that the dormant red buds are one inch below the soil’s surface. If too shallow, the buds may be killed by exposure, if too deep the plant may not flower. Plant peonies where they will receive at least six hours of full sun. More is better. Peonies don’t need particularly rich soil and adapt to clays quite well. Dig in a generous amount of compost and a big handful of some form of phosphate. Water the newly planted root generously to start then occasionally through the fall. Do not keep them soaking wet.