What is the proper way to divide peonies?
September is the best time to divide peonies. By September, peony plants have been able to store adequate food reserves in their roots. Also, the replanted divisions have several weeks to get reestablished at their new sites before the onset of winter.
Begin by cutting the peony stems near ground level. Carefully dig up the plants and wash or gently shake off the soil. Using a sharp knife, divide the clump into sections. Each section should have three to five buds (eyes) and a good root system. Divisions with fewer than three buds may take 2 or more years to flower.
When planting, dig a hole large enough to accommodate the root system of the peony. Position the peony in the hole so the buds are 1 to 2 inches below the soil surface. (Plants may not bloom well if the buds are more than 2 inches deep.) Fill the hole with soil, firming the soil around the plant as you backfill. Then water thoroughly. Space peonies 3 to 4 feet apart.
Mulch newly planted peonies with several inches of straw or pine needles in late fall. Mulching prevents repeated freezing and thawing of the soil that may heave and damage young plants. Remove the mulch as growth resumes in spring.