While both tree peonies (*Paeonia suffruticosa* or *P. rockii*) and herbaceous peonies (*Paeonia lactiflora* and others) belong to the genus *Paeonia*, they are distinct in their growth habits, physiology, and, consequently, their care requirements. Understanding these botanical differences is key to cultivating them successfully.
The most fundamental difference lies in their growth habit. Herbaceous peonies are perennial plants. Their soft, herbaceous stems and foliage die back completely to the ground each winter, with new growth emerging from their underground crown and tuberous root system each spring. In contrast, tree peonies are deciduous woody shrubs. They develop a permanent, above-ground woody framework of stems and branches. While they drop their leaves in autumn, the woody structure remains intact throughout the winter, and new growth emerges from these existing branches in spring. This structural difference dictates their placement, pruning needs, and winter protection.
This is a critical care difference rooted in their morphology. Herbaceous peonies have specific bud structures called "eyes" on their crown. For successful flowering, these eyes must be planted at a precise depth of no more than 2 inches (5 cm) below the soil surface. Planting too deep is a primary reason for herbaceous peonies failing to bloom. Tree peonies, however, are almost always grafted onto a herbaceous peony rootstock. They must be planted with the graft union—a noticeable bulge on the main stem—located 4 to 6 inches (10-15 cm) *below* the soil surface. This deep planting encourages the tree peony scion to develop its own roots and ensures the long-term health and stability of the plant.
Their contrasting structures demand entirely different pruning approaches. For herbaceous peonies, maintenance is simple: in late autumn or early spring, all stems are cut back to ground level to remove dead material and prevent disease. Pruning during the growing season is generally limited to deadheading spent flowers. Tree peonies require a more nuanced approach. Pruning is done in early spring before bud break and is focused on maintaining the shrub's shape and encouraging vigor. This involves removing any dead wood from the woody framework and potentially thinning out weak or crossing branches. Unlike herbaceous types, you should never cut a tree peony to the ground.
As herbaceous plants that retreat underground, herbaceous peonies are extremely cold-hardy and generally require no winter protection in their suitable zones. The tree peony's woody stems, while hardy, can be susceptible to winter damage from desiccating winds and harsh sun, which can kill the flower buds held on the branches. In colder climates (USDA zones 4-5), it is often recommended to provide a loose winter mulch (like straw or pine boughs) around the base and to shield the plant with a burlap screen to protect the buds. This is not necessary for the plant's survival but for optimal flowering.
Both types are long-lived plants, but tree peonies are renowned for their exceptional longevity, often thriving for a century or more. A key care consideration is patience. Herbaceous peonies may take 2-3 years to become established and bloom well after planting. Tree peonies require an even longer period to settle in; it is not uncommon for them to take 3-5 years to begin flowering significantly as they devote energy to building their extensive root system and woody structure. Once established, however, they become incredibly resilient and low-maintenance fixtures in the garden.
