Paeonies are rhizomatous plants that often have thick, tuberous roots. Their leaves are alternate, compound and often pinnate. Flowers are solitary to many, and are terminal. There are five green sepals, and five to ten petals per flower, and two to eight carpels. Flower colour ranges from red-purple to pink, yellow or white. The fruit comprises a spreading, hairless or hairy dry, dehiscent fruit derived from a single carpel (follicle). Seeds may be covered with a fleshy coloured outer layer.
Paeonies are long-lived perennials and are divided into two distinct groups, namely (1) herbaceous perennials, which include the many garden forms, and (2) shrubby perennials or the Mountain or Tree Paeonies (largely derived from Paeonia suffruticosa).
Paeonies are very suitable for herbaceous or mixed shrub beds or borders. They are grown for their foliage, which in some cultivars assumes a rich copper and red tints in the spring and autumn. They are also prized for their beautiful bowl-shaped single or double flowers.
Established paeony plants are best left undisturbed, yet they are gross feeders which may live 20 to 50 years in one site. Therefore, it is advisable to prepare the site very thoroughly before planting. Fork in generous quantities of well-rotted manure or compost, with bone meal or superphosphate into the planting hole. This should be done about two weeks before planting to allow for soil settlement. Crowns should be firmly set not lower than 25 mm below the surface to ensure flowering. This must be done with care so as not to damage the 'eyes' or roots. Where moving of an established clump becomes necessary, do so with a large root ball, and keep well watered until re-established.
Paeonies are lime-tolerant, and may be grown on any moist, fertile soil which drains well. The soil depth should not be less than 30 cm. Plants should be spaced 60-90 cm apart (depending upon the species) in early autumn or spring. They can be grown in full sun or partial shade. Hoe in bonemeal at planting time. Clumps will have to be supported with hoops or grown through a plant support when the foliage is half grown.
Cultivars of herbaceous paeonies may be propagated by division. Each division should comprise three stout shoots, 10 to 15 cm, with 3 to 5 'eyes'. If smaller pieces are used, they will take longer to flower. The plants should be lifted carefully, and left to stand for several hours in the shade so that the roots become less brittle. A sharp knife should be used to effect divisions. Then, dust each with fungicide before replanting.
All paeonies can be raised from seed but named varieties and hybrids will not come true. Sow firm ripe seeds in the autumn, and leave the pots outside all winter or collect seed when ripe, and store in the refrigerator. To stimulate the seeds to germinate, place them in small plastic bags with wet sand and leave in the refrigerator for about 6 to 8 weeks before sowing. This process, called stratification, will break the seed's dormancy.
Paeonies are available in single to anemone to double. Once established, they are remarkably drought tolerant.