Tree Peonies for Spring Planting. The Tree Peony (Paeonia suffruticosa) is one of the most glorious shrubs known to man. Mature plants reach 4-5ft and carry up to 50 huge, silky blooms. Tree Peonies grow best in full sun or partial shade (required in the South and warm areas of westerns Zone 9) and evely moist but well-drained soil with a pH close to neutral. We ship 3-year-old, grafted, 12-18in bareroot plants. They take a year or two to show what they can do. Hardy, disease- and (best of all) deer-resistant.