The cultivar 'Hanabi' is an early blooming selection with double flowers.
Not really a tree, the so called tree peony is a sparsely branched woody shrub, often with numerous basal suckers, that gets only about 5-10 ft (2.1-3 m) tall. Most specimens never exceed 5 ft (1.5 m) in height. The branches tend to be lax and spreading, and thus the shrub has a width about the same as its height. The twice pinnate leaves are dark green above and bluish green beneath, with nine ovate leaflets, each with deeply dissected and pointed lobes. The flowers of the tree peony are very similar to those of the garden or Chinese peony (Paeonia lactiflora), which is not a shrub, but rather an herbaceous perennial. Single cup-shaped flowers in white, pink, red or purple are produced in late spring. Most varieties have a magenta blotch at the base of each of the many petals. The flowers are generally 6-8 in (15-20 cm) across, but some varieties have flowers fully 12 in (30 cm) across! Many of the cultivars of tree peony have fragrant flowers.
Horticulturalists have created a lot of beautiful hybrids with other tree peonies from China, especially with the yellow flowered P. lutea and the maroon flowered P. delavayi. Many cultivars from these crosses are available in the trade. 'Joseph Rock' is a very popular tree peony that has semi-double flowers that are white with maroon blotches at the base of the petals; 'Banksii' has double flowers that are pink with white tips; 'Mrs. William Kelway' has double white flowers; 'Reine Elisabeth' has double pink flowers with ruffled margins; the spectacular 'Rimpo' has flowers up to 12 in (30 cm) across that are dark purple with bright yellow stamens.
The tree peony, Paeonia suffruticosa, is native to thin woods and open areas in the mountains of western China, Bhutan and Tibet.
Tree peony cultivars are typically grafted onto rootstock of P. suffruticosa, the species, or onto one of the many herbaceous species, especially P. lactiflora and P. officinalis. It is recommended that plants be set in the ground so that the graft union is 5-6 in (12-15 cm) deep in order to encourage roots to form on the scion. Tree peonies don’t need much pruning: Just remove unwanted suckers, dead wood and side shoots. They do have a reputation of being not easy to grow, and they are known to be rather slow growers. Light: Tree peonies thrive in full sun to partial shade. Partial shade is best in the more southern parts of the range. They seem to flower best in dappled shade with 2-3 hours of full sun during the day. Moisture: Tree peonies like a cool, moist but well drained, neutral to basic soil. Mulch around the base to keep the soil under the plant moist and shaded. Water regularly. Hardiness: USDA Zones 4-8. Tree peonies do best with a good hot summer and a relatively long period of winter cold. They need a cold winter dormant period, but can be damaged by a late frost. Provide afternoon shade above zone 7, and mulch for winter protection below zone 6.
Propagation: Fast growing stem tip cuttings taken in spring sometimes can be rooted, but semi-hardwood cuttings taken in late summer take root more reliably. Commercially, tree peony cultivars are propagated by grafting onto rootstocks of herbaceous species. A wedge shaped scion only about an inch (2.5 cm) long and with a single leaf is inserted into a slit in the rootstock. When planting out, the junction of the scion and rootstock is buried to encourage the scion to develop its own roots.
Tree peonies are deciduous woody-stemmed plants that bloom in late spring or early summer depending on climate and variety.
Although the ancient Chinese cultivated the herbaceous peonies mainly for their medicinal value, they grew and developed the tree peonies for their ornamental qualities. A happy tree peony is truly a beautiful specimen. In springtime the flowers are extremely showy and the foliage continues to look good all summer. In the winter the tree peonies have lost their leaves, but still display a branching structure that is rather graceful and not at all unsightly.
Tree peonies are known for their aggressive suckering tendencies, and might be useful in deciduous hedges or borders where a few extra stems would be desirable. They also make excellent accents along driveways or paths, and are very well suited to the woodland garden. Like the herbaceous peony flowers, tree peony blossoms are excellent as cut flowers.
Tree peonies have brittle stems and singletons should be protected from strong winds, and flowering branches should be staked to prevent breakage. Cultivars grafted onto rootstocks from herbaceous species tend to be short lived unless they can be induced to develop roots on the scion itself.
The peony genus has 33 species. All hail from temperate Europe or Asia except for two that are native to the North American West Coast. Learn more about peonies at the American Peony Society.
WARNING Apparently all of the peonies are mildly toxic and no parts should be ingested.