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 the 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 they need a significant period of cold winter temperatures each year.
Noteworthy Characteristics
Paeonia ostii, commonly known as Osti’s tree peony, is a deciduous, multi-stemmed, woody shrub that typically grows to 3-5’ tall and as wide. It is an endangered species that is native to Henan (Lushi Xian) province in China, but is cultivated in several additional areas including Anhui, Hubei, Shaanxi and Sichuan provinces. It is primarily found in broad-leaved forested areas and thickets on slopes at altitudes of 2500’ to 5000’. It was first published in 1992 and originally called P. suffruticosa subsp. ostii.
Brownish gray stems are clad with large 2-pinnate leaves. Each leaf is divided into 11-15 lanceolate to ovate-lanceolate leaflets, with each leaflet being 2-5” long. Solitary, terminal, single, sweetly fragrant white flowers (to 6” wide) have purple-red filaments, disc and style with contrasting yellow anthers. Flowers bloom April-May.
Species plants are grown in China for use as a traditional medicine.
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 Dr. Gian Lupo Osti, Italian peony expert.
‘Feng Dan Bai’, commonly marketed under the trade name of PHOENIX WHITE, typically grows to 4-5’ tall and as wide. It features upward facing fragrant white flowers (to 7” across) with slightly ruffled petals.
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
Tree peony for prominent areas of the landscape where its spring flowers can be easily observed and enjoyed. Effective as an accent, specimen or in groups. Flowers are extremely showy, and foliage remains attractive throughout the growing season, either alone or as a frame or backdrop for other flowering plants.