Every once in awhile a plant comes along that hits the region by storm like Wave petunia and Vanilla Strawberry hydrangea. What’s the latest? Itoh peonies, and we’ll be hearing a lot more about them as word spreads.
Most of us are very familiar with beautiful old-fashioned peonies (called herbaceous peonies) that have been popular since great-grandma’s day. But there are other species of peonies that are less-well known, such as tree peonies that develop into a rounded woody shrub. Unlike herbaceous peonies that die back to the ground each winter, tree peonies maintain their buds above ground on woody stems. Tree peonies are occasionally grown in the Upper Midwest, but have never become widely popular, although they’re listed as Zone 4 or Zone 3 in a protected spot.
After years of saying it couldn’t be done, in 1948 Japanese horticulturist Toichi Itoh successfully crossed the old-fashioned herbaceous peony with the tree peony, after thousands of failed attempts. Unfortunately he didn’t live to see the successful hybrid come into flower. Itoh’s widow kept the hybrids, and years later an American horticulturist purchased the plants, brought them to the United States, and began propagating and developing the hybrids. This group of peonies is officially called “intersectional hybrids” and nicknamed “Itoh hybrids” after their originator.
The first plants that became available sold for $500 to $1000 each because of their rarity. It’s taken decades for the Itoh hybrids to be propagated in quantities that brought the price down, making them affordable for home gardeners. During the past several years Itoh peonies are increasingly seen at regional garden centers, and we’ll probably be seeing a lot more as they become well-known.
What’s so special about Itoh (intersectional hybrid) peonies?
- A mature plant can produce 50 dinner plate-sized flowers with unique form.
- Foliage is lush, deep green and attractive through the season, less prone to gray powdery mildew than herbaceous peonies.
- Flowers are borne on strong stems that don’t require stakes or cages, and have less tendency to flop apart like some peonies.
- Plants grow about 3 feet high and wide.
- Hardiness is Zone 4 into Zone 3, which makes them winter-hardy for much of our Upper Midwest region, and Itoh peonies have been successfully grown by area gardeners for a number of years.
- They have the flower and foliage of tree peonies, but die back to ground level like herbaceous peonies.
- They bloom slightly later than herbaceous peonies. They bloom for a longer time period – usually 2 to 3 weeks, with waves of blooms coming as new buds open.
How to care for Itoh peonies:
- Care is very similar to old-fashioned herbaceous peonies.
- September is the preferred month to dig, divide and plant.
- The crown, where stems meet roots, should be one-and-one-half inches below final soil surface.
- As with other peonies, Itoh types require about 3 years to develop into well-blooming plants.
- Mature Itoh peonies usually develop woody portions several inches above soil level, and spring buds often emerge from both below ground, and from the woody stems close to ground level. When cutting back the foliage in the fall, cut back to about 5 or 6 inches above ground level, instead of 1 to 2 inches as is done with herbaceous types.
Named varieties of Itoh peonies on the market include Bartzella (the yellow variety pictured, which has been one of the more common), Cora Louise, Going Bananas, Julia Rose, Keiko, Kopper Kettle, Misaka, Morning Lilac, Yumi, Sequestered Sunshine, Singing in the Rain, Yankee Doodle Dandy and more. Often on the plant tag, they will be labeled ‘Bartzella Itoh’ peony, etc.