Herbaceous peonies are tough, hardy plants that outlast sub-zero winters and jauntily spring back after dying to the ground. Their thick roots store energy for attractive dark green foliage that sets off the large flowers in spring, ensuring their popularity in cool summer gardens. Peonies were so popular that pioneers carried the tubers into the northern United States, and peony nurseries date to the 1800s. However, this plant, despite its pioneer heritage, hates to be moved and can be tricky to transplant.
Plant peonies in early fall, in September to October. Choose tubers with three or more eyes and check them for signs of rot. North Carolina State University's Department of Horticulture recommends cutting away any soft areas of the tuber with a sharp knife.
Choose a well-drained planting site in full sun. Dig a hole 12 inches deep and 18 inches wide. Add 2 to 4 inches of compost or aged manure and ¼ cup of a balanced, 10-10-10 fertilizer into the bottom of the planting hole. Fill the hole halfway and mix in the compost. Add another layer of soil to prevent fertilizer from burning new roots.
Place the tuber in the hole, eyes upward, and backfill around the roots. Keep the peony's crown 2 inches below the soil surface. Plant the tubers too deep, and the peony will delay blooming as it resettles itself, warns the Heartland Peony Society. Firm the soil and water well.
Divide peonies when they have become crowded, usually after 10 to 15 years, suggests the NCSU horticulture department. Fall is the best time of year to divide peonies. Soak the plant well the day before to loosen the soil. Dig around the plant, keeping as many roots as possible. Lift the plant.
Prune all the foliage and wash dirt from the crown and roots. With a sharp, clean knife, cut the original tuber into sections, each with five eyes. Choose new planting sites 3 to 4 feet apart and quickly replant the tubers.