Peonies are long-lived garden plants that bloom in late spring and early summer. Proper annual pruning is necessary to maintain health and ensure robust flowering. The timing and technique of cutting back differ significantly depending on the variety. Understanding these distinctions is important for garden success.
The Timing and Method of the Main Fall Cutback
The herbaceous peony requires a significant cutback each year to prepare for winter dormancy and prevent disease carryover. This pruning should occur in late fall or early winter, after the first hard frost has caused the foliage to turn yellow or brown. Allowing the leaves to remain green permits the plant to continue photosynthesis, storing energy in its root system for the next season’s growth and bloom production.
Once the foliage has died back naturally, the stems should be cut down to one to three inches (2.5 to 8 cm) above the soil line. This removes the entire above-ground structure, which is necessary for disease management. The old plant material often harbors fungal spores, such as Botrytis paeoniae, which causes botrytis blight.
Removing the infected material prevents these spores from overwintering and infecting new shoots in the spring. Gather all cut stems and foliage and dispose of them away from the garden. This debris should not be added to a home compost pile, as the temperatures are insufficient to kill the fungal pathogens.
Maintenance Pruning: Deadheading and Spring Cleanup
Routine maintenance is performed during the active growing season, separate from the main fall cutback. Deadheading, the removal of spent blooms, should be done immediately after the flowers fade. This prevents the formation of seed pods, redirecting energy toward strengthening the root system for the following year.
To deadhead correctly, cut the flower stem back to the first set of strong, healthy leaves below the spent bloom. Leave the remaining foliage intact to allow the plant to photosynthesize throughout the summer. This preserves the green leaves until fall.
A minor cleanup can occur in the early spring before new growth emerges. This involves removing any old, brittle stem sections missed during the fall cutback or damaged material from winter weather. Spring cleanup should be limited to surface debris and broken stems only.
Pruning Requirements for Tree and Intersectional Varieties
Tree peonies are woody shrubs and are treated differently because their stems do not die back to the ground each winter. These varieties require minimal pruning, primarily for shaping or removing compromised wood. Shaping or size reduction should be done selectively in late spring after flowering, or in early spring before new growth begins.
The woody structure of the tree peony is permanent and should be preserved. Cuts should only be made to remove dead, diseased, or crossing branches. Removing entire healthy stems will reduce the plant’s size for many years, as tree peonies regenerate large woody growth slowly. When removing dead wood, cuts should be made back to a healthy bud or to the ground level.
Intersectional, or Itoh, peonies are hybrids combining traits of both tree and herbaceous types, possessing a semi-woody stem structure. Like herbaceous peonies, Itoh varieties should be cut back hard in the fall after the foliage has died back naturally from frost. The stems should be reduced to about four to five inches above the soil line, removing the bulk of the year’s growth.
This annual severe cutback is necessary because Itoh peonies produce new buds from the ground each spring. This pruning helps control the plant’s size and prevents the buildup of fungal spores. The leaves should still be removed completely from the garden site to maintain plant health.