Herbaceous peonies are the most common form of peony. They have green bushes and leaves that exist all summer. They are disease resistant and the oldest form of peony. They are often the types florists use for arrangements due to their long stems. They are deer-proof and bloom every year.
Tree Peonies are distinct from herbaceous peonies in that they have woody shrubs. Their woody composition supports very large blossoms. After they bloom, tree peonies maintain dark, healthy leaves that last through the fall. Tree peonies are rare, with very large flowers with great leaf coverage and therefore, great for landscaping!
A hybrid, known as the intersectional peony (or ITOH, named after its original hybridizer Toichi Itoh) is the result of crossing the herbaceous and the tree varieties. These hybrids boast the best traits of both types, having the large, beautiful blossoms of the tree species, but the lovely green foliage and hardy, quick growing nature of the herbaceous peonies. Most ITHOs do not leave bare woody stems above ground in winter
Full-double peonies are a species that complete the process of turning all stamens and carpels into petals. Therefore, they present as a thick, dense and round composition of petals.
Semi-Double peonies don't fully complete the process of turning stamens and carpels into petals - although they have many layers of guard petals. They open to show a center of smaller petaloids and stamens.Shop Semi-Double Bloom Peonies
Singles have a row of guard petals that delicately surround a center of stamens.
Japanese peonies have started the process of doubling. The filaments, stamens and anthers become incredibly large. This bloom-type often draws attention more to it's remarkable, protruding center, over its "bowl" of guard petals.
Bomb-type peonies are aptly named in that their centers have a a circular "explosion" of petaloids resembling softballs. They are surrounded by a flat layer of larger guard petals.