Culture
Best grown in deep, fertile, organically rich, neutral to slightly alkaline, medium moisture, well-drained soils in full sun to part shade. Best in part shade. Tolerant of summer heat. Add compost as needed before planting. Larger shrubs appreciate some shelter from strong winds, particularly when in flower. Unlike herbaceous peonies, the stems of tree peonies (which are woody plants) do not die to the ground in winter and should not be cut back after frost. No pruning is required, except to cut out dead wood or suckers in early spring. If plants become leggy, a moderate pruning in early fall can be done to shape plant and encourage additional growth on the lower part of the plant. Remove spent flowers after bloom. These long-lived plants usually take several years to establish, and are best left undisturbed once planted. Moreover, plant roots go deep and transplanting can be difficult. Plants will not always perform well in mild to warm winter climates (south of Zone 8) because, as alpine natives, they need a significant period of cold winter temperatures each year.
Noteworthy Characteristics
Paeonia delavayi, commonly known as tree peony, is a deciduous, multi-stemmed, woody shrub that typically grows to 3-5’ tall and as wide. It is native to open woodland areas and grasslands in western China from Sichuan and Yunnan to southeastern Tibet, growing primarily at altitudes of 9,000 to 11,000’.
Flora of China currently describes the petal color of species plants as “yellow, yellow with a red or purple-red spot at base, red, dark red or dark purple-red, sometimes white, green-yellow, yellow with a red margin, or orange.” Plants of this species are widely variable in regard to a large number of characteristics, including leaf structure, leaf and flower size, and flower color. Taxonomists are in disagreement as to which plants should be included in the species and, of those included plants, which ones should be listed as designated varieties or subspecies and which should be simply included as synonyms.
P. delavayi as originally described produces saucer-shaped flowers (to 3" across) which typically have maroon to dark red petals with red-purple anthers. Flowers bloom in May. Flowers are followed by pod-like fruits. Large leaves are deeply divided into numerous lance-shaped to oval leaflets (entire leaf blade to 6-12” long). Leaves are dark green above and blue-green beneath. Foliage remains attractive throughout the growing season. No fall color.
Var. lutea (from Latin meaning yellow) features flowers with bright yellow petals and yellow anthers. It was first described in 1886 and given the name of Paeonia lutea. In 1904, some experts decided that P. lutea should be included as a variety under P. delavayi. But disagreement among taxonomists continues to exist. At present: some experts claim that var. lutea does not warrant recognition as a variety, but is simply a synonym of P. delavayi. Moreover, there remain some experts who continue to believe that this yellow-flowered peony belongs in its own species P. lutea as originally described. The Missouri Botanical Garden currently considers this plant to be a yellow-flowered variety of P. delavayi.
Flowers have deep pink veins and purple flares. It typically grows to 3-5’ tall.
Genus name comes from the Greek name for Paeon, physician of the gods and reputed discoverer of the medicinal properties of plants in this genus.
Specific epithet honors Father Jean Marie Delavay (1834-1895), French Catholic missionary who collected plants in China.
Problems
Tree peonies are considered to be relatively pest free. Some susceptibility to canker, leaf blight, stem wilt, honey fungus, and scale. Ants on peony buds are common and totally harmless.
Uses
Excellent in borders as specimens and in groups. Also effective as accents or hedges along fences, sidewalks, driveways or walls. Flowers are extremely showy, and foliage remains attractive throughout the growing season, either alone or as a frame or backdrop for other flowering plants.