Two different kinds of peony plants are cultivated in the United States. Tree peonies, or Paeonia suffruticosa, have a shrub-like form and produce abundant flowers, while herbaceous peonies, or Paeonia officinalis, are perennial flowering plants. Herbaceous peony forms vary by cultivar.
Herbaceous peonies are classified and grouped depending upon their flower shapes. Some cultivars produce anemone blossoms, which have outer rows of large petals that surround narrow inner petals. Japanese blossoms resemble the anemone form, but they also have non-pollen bearing stamens in the center. Single peonies have outer blossoms that surround pollen-bearing stamens, while semi-double peonies have broad petals mixed among pollen-bearing stamens. Double peonies only have petals in the center.
Herbaceous peonies grow between 2 and 4 feet tall. They are available in nearly every color except for blue; common peony colors include pink, yellow, white, crimson and black, among many others. Several available cultivars include ‘Nippon Beauty,’ a red Japanese variety with red petals and a red and yellow center, and ‘Nick Shaylor,’ a blush pink double peony.
Herbaceous peonies are cold-weather plants that grow best in USDA Zones 2 through 8. They require a winter cold period to flower. They prefer full sunlight and well-drained soil, preferably with a pH level between 6.0 and 7.0, and tolerate a variety of soil types. Peonies are susceptible to several diseases including botrytis blight, verticillium wilt, phytophthora blight and leaf blotch, as well as attacks from scale insects