Peonies, members of the genus *Paeonia*, are beloved for their magnificent blooms. They are primarily categorized into three distinct types: herbaceous, tree, and the hybrid Itoh peonies. Understanding their differences requires an examination of their botanical growth habits, stem structure, and lifecycle.
Herbaceous peonies are the most common type. From a botanical perspective, they are non-woody perennial plants. Their growth cycle is complete each year: in spring, new shoots emerge from underground storage organs called buds or "eyes" on a root structure known as a crown. These shoots grow rapidly, producing stems, leaves, and flowers. The stems are soft, green, and photosynthetic. Crucially, the entire above-ground structure—stems, leaves, and spent flowers—dies back completely to the ground level after the first hard autumn frost. The plant survives the winter through its dormant crown and roots below the soil surface, storing energy to repeat the process the following spring. They typically bloom in late spring to early summer.
Tree peonies are actually deciduous woody shrubs, not trees. This is their most defining characteristic. Unlike herbaceous types, they form a permanent woody framework of stems and branches that persists year-round. They do not die back to the ground in winter. New growth in spring emerges from the buds on these existing woody stems, which continue to grow larger and more intricate with each passing year. This woody structure allows them to grow much larger, often reaching 4-7 feet in height and width. Their bloom time is generally earlier than herbaceous peonies, and their flowers are often much larger. The plant's energy is stored in its woody branches and root system.
Itoh peonies, also known as intersectional hybrids, are the result of successful cross-breeding between herbaceous (*Paeonia lactiflora*) and tree (*Paeonia suffruticosa*) peonies. They represent a unique combination of the best traits of both parents. Botanically, their growth habit is their most distinguishing feature. Similar to herbaceous peonies, their stems and foliage die back to the ground in the winter, meaning they do not leave a woody structure above soil level. However, the plant's form during the growing season is more like a tree peony; the stems are sturdier and the plant has a shrub-like, mounded appearance. They also inherit the large, often multi-colored flowers of tree peonies but with the prolific flowering nature of herbaceous types. Their strength comes from a robust, woody root system that supports the vigorous herbaceous top growth each spring.
