There are two groups of peonies: herbaceous ones that are grown in borders and tree peonies which grow as lax shrubs. They are mainly grown for their very attractive flowers, but many also have attractive foliage, both in spring and in autumn, as well as having good seedpods in autumn.
The flowers come in singe, semi-double and double forms, the last being especially popular. The colours vary from white through pink to red. There are also yellow species and varieties. The main flowering season is from spring through the summer.
The plants have deep fleshy tap roots that do not like to be disturbed. If you do move a peony it may take several years to settle down. Such roots also make them unsuitable for container culture.
Peonies need a deep rich soil with plenty of well-rotted organic material added to it. They prefer a sunny position but will grow in a very light shade. The double-flowered forms may need some form of staking to prevent them flopping. This is especially a problem during rain as the already heavy flower heads fill with water. Most are hardy but buds, flowers and foliage can be damaged by late frosts.