Tree peonies are generally the biggest of all peonies, reaching anywhere between a meter and three meters tall. They bloom abundantly, often producing up to 100 large flowers per tree. Each flower can measure up to ten inches across.
Herbaceous peonies are smaller than tree peonies, rarely exceeding a meter in height and generally growing in a small bush-like formation. They produce fewer blooms than the tree peony, usually between 40 and 50 individual flower heads per plant.
Itoh peonies are an intersectional group that was created by Japanese horticulturist Toichi Itoh in 1948. Itoh created these hybrids to display the best qualities of both the herbaceous peony and the tree peony.