The Itoh peony, also known as the intersectional peony, is a hybrid that combines the best qualities of its parent plants: tree peonies and common herbaceous peonies. As a result, Itohs have enormous, long-lasting blooms and strong stems, as well as dark green, lush, deeply lobed foliage that lasts until autumn. With flowers that can spread up to 8 inches across, Itoh peonies are available in a variety of vibrant colors including yellow, coral, pink, red, and white.
Although the foliage grows fairly quickly, these are relatively slow-maturing plants, and seedlings may require three or four years before they begin to bloom. However, potted nursery plants are usually at least two years old before they are sold, and a good healthy one-gallon nursery specimen may provide you with blooms in its first year. If you are buying mail-order bare roots, expect rather slow growth in the first year or two.
Peonies are mildly toxic to dogs, cats, and horses, due to the presence of paeonol in the leaves, roots, and stems.
|Common Name||Itoh peony, intersectional peony|
|Botanical Name||Paeonia cvs.|
|Plant Type||Herbaceous, perennial|
|Mature Size||3 ft. tall, 4 ft. wide|
|Sun Exposure||Full, partial|
|Soil Type||Rich, well-drained|
|Soil pH||Slightly acid to neutral (6.0 to 7.0)|
|Bloom Time||Late summer|
|Flower Color||Yellow, coral, pink, red, white|
|Hardiness Zones||3a–8a (USDA)|
|Native Area||Nursery hybrid|
|Toxicity||Toxic to pets|
Itoh Peony Care
Itoh peonies are planted in much the same way as standard herbaceous peonies. When purchasing potted nursery plants, it's best to plant them as soon as possible rather than letting them remain in pots for too long. Remember that they are large plants, so space them 3 to 4 feet away from other plants or other peonies.
Itoh peonies are best planted in the spring, as soon as the ground can be worked. Prepare the planting hole adequately, blending in amendments, if needed, to improve the soil's drainage. In colder zones, plant peonies a little deeper, with about 2 inches of soil covering the root ball. In warmer climates, the root ball can be just barely covered. Do not cover the root area with mulch or too much soil, as this can smother the roots and reduce blooming.
These plants are largely trouble-free once established, though they do need regular feeding. Since Itoh peonies have inherited the tree peony’s strong stems, gardeners don’t have to worry about staking since they are unlikely to bend over in wind and rain. They are also somewhat resistant to the various types of peony blight (botrytis and phytopthora) that are sometimes problems with herbaceous peonies.
The Itoh peony’s foliage will grow densely in full sun, but its flowers will typically last longer if the plants enjoy some light shade.
Water Itoh peonies in spring as new growth emerges, provided there's no natural rainfall for more than two weeks. Water lightly twice a week (no more than 1/2 inch at a time), but avoid drowning the soil. Ground-level soaking is generally better than overhead watering, which can splash fungal spores from plant to plant.
Be sure to plant Itoh peonies in rich, well-drained soil. These plants react badly when planted in dense, water-retentive soil. Make sure to amend with plenty of organic matter if your soil is not porous.
Temperature and Humidity
Itoh peonies are known to be cold-hardy, surviving winter temperatures below minus 25 degrees Fahrenheit. But in addition, Itoh hybrids work well in warmer climates, such as the temperatures in zone 8. They do not do well where winter temperatures stay above freezing, since they require a cool period to reset themselves for blooming the following spring.
Itoh peonies tolerate a range of humidity levels, though prolonged cool, humid conditions can encourage fungal diseases.
Peonies should get three good feedings a year: in the early spring as shoots appear; when the flower buds are just appearing; and in the fall to support root development before winter. When fertilizing your Itoh peonies in the spring and summer months, use a balanced 10-10-10 fertilizer; the fall feeding is best done with a 5-10-10 formulation. Itoh peonies seem to particularly enjoy foliar feeding with a water-soluble fertilizer.
Types of Itoh Peony
There are many varieties of Itoh peony to choose from, with a surprising range of flowers colors, sizes, and shapes. When choosing a variety, pay attention to the hardiness zone ratings, as some are not tolerant of zone 3 cold.
Here are some popular varieties:
- 'Garden Treasure' has large, golden-yellow double flowers. It grows up to 30 inches tall and 5 feet wide.
- 'Border Charm' is a smaller, 2-foot-tall plant with medium-sized semi-double yellow flowers.
- 'New Millenium' has coral pink semi-double flowers on 28-inch-tall plants.
- 'Bartzella' has very large bright yellow double blossoms with a slight red center stain; flowers have a slightly spicy scent. Plants grow to 36 inches.
- 'Keiko' has large, semi-double to double flowers; dark lavender-pink petals fade to a soft pink.
- 'Yankee Doodle Dandy' features semi-double to double blooms of deep pink with cream undertones. It grows to 36 inches tall.
- 'Takara' has unusual flowers, yellow with deep lavender-pink, on 24- to 30-inch plants.
- 'Singing in the Rain' has creamy yellow flowers that become gradually flushed with salmon. It grows 2 to 3 feet tall.
Itoh peonies can be deadheaded on an as-needed basis throughout the spring and summer months. Deadheading will stimulate the plant into producing additional waves of blossoms. In the fall, cut them about 4 to 6 inches from the soil level—or to wherever the stems die back to. Like herbaceous peonies, Itoh peonies will come back in the spring from the ground.
Propagating Itoh Peonies
Root division is the traditionally effective method of propagating all Itoh peonies. But be aware that peonies do not like to be disturbed, and division should be done only when you want to propagate new plants. It will take a couple of years for the replanted pieces to settle in and become vigorous again. Here's how to do it:
- In the early spring before active growth has started, dig up the entire root ball with a shovel.
- Rinse off the roots so you can see the root ball clearly, then divide the plant into pieces with a sharp knife, cutting through the crown. Make sure each piece has a least one strong root and three to five eyes exposed at the top of the crown.
- Plant the pieces in new locations, with the eyes just below the surface of the soil. It's best to plant quickly rather than storing the roots for too long before replanting.
How to Grow Itoh Peonies From Seed
The seeds of Itoh peonies are not viable. Root division is the only practical means of propagation.
Potting and Repotting
Although it's not the normal practice, Itoh peonies can be grown in pots. Itoh peonies have large roots, so, when potting, be sure to choose a container that’s a minimum of 18 inches wide and deep. The pot should also have excellent drainage. Though they can tolerate some cold, it's recommended to move your container plants indoors for the winter, where they will need as much sunlight as you can provide.
Make sure the plants are well-watered in the weeks leading up to frost. Remove and dispose of the plant's leaves before winter sets in, to avoid fungal spores from overwintering. When the stems turn brown and brittle, clip them off to just above ground level, but be careful not to clip off the crown growth buds. No other winter protection is needed—mulch can work against the plant's health.
Common Pests and Plant Diseases
Itoh peonies are much more resistant to the common problems that plague common peonies, but you may still encounter some of these:
- Several types of beetles, especially chafer beetles and Japanese beetles, can feast on the plant's buds and flowers. You can hand-pick the beetles off the plant, or use almost any pesticide to control them. A good non-toxic option is neem oil.
- Powdery mildew is a fungal disease that coats leaves with a whitish-gray powdery residue. While unattractive, it is seldom deadly. Prevent the disease by watering through ground-level soaking rather than overhead spraying, which can splash the ground spores onto the plants. Coating the plant with neem oil when it first leafs-out can prevent the disease from gaining a foothold.
- Botrytis is a potentially deadly fungal disease, but one that can be treated by repeatedly removing affected plant parts, or with heavy doses of an appropriate fungicide. It is most common during prolonged periods of cool, wet, humid weather.
How to Get Itoh Peony to Bloom
If you've properly planted a fully developed one-gallon specimen, you can expect 30 blossoms in the first couple of years and up to 60 on a mature bush. With a bare root plant, it can sometimes take a couple of years before it blooms robustly. If an established plant fails to bloom, there are several possible reasons:
- The peony has been planted too deep: The roots of the peony should be no more than 2 inches below the surface—or even shallower in warmer climates. Many gardeners find that lifting the plant just an inch or two in the soil can cause the plant to bloom more vigorously.
- Not enough sunlight: If nearby trees and shrubs have grown up and begun to shade your peony, some good hard pruning of those surrounding plants may return your peony to vigorous blooming.
- Not enough fertilizer: Peonies, like other robust flowering plants, needs regular feeding to support blooms.
- Improper deadheading: It's not always easy to distinguish the developing buds from the spent flower heads. If you've mistakenly pinched off the young buds during deadheading duties, your peony will lose potential flowers.
- Weather problems: Though Itoh peonies have a broader hardiness range than most peonies, a late frost in the northern part of the range can kill off the early flower buds and ruin the early-season blooms. And in the warmer part of the range, if winter has been unseasonably warm, the peony will lose out on the chill period the plants require to reset themselves. These problems are just temporary, as the plant will return to normal blooming the following year.
Common Problems With Itoh Peony
Stems Wilt, Buds Die Back
Though not common, Itohs, like other peonies, can be affected by botrytis fungus that causes these symptoms. Botrytis can be cured if caught early, sometimes merely by cutting off and destroying affected plant parts. A variety of fungicides can also kill the disease.
Leaf Splotches and Spots
These symptoms are generally a sign of some type of fungal infection. Such infections are rarely fatal and can be handled by removing and destroying affected plant parts. Keep the ground area free of debris to prevent the fungi from overwintering and returning next year. Severe cases can be treated with a systemic fungicide.
Ants Cover the Flowers
Ants covering peony buds and flowers pose no problems whatsoever unless you want to clip the flowers and bring them indoors for display. Ants are drawn to peonies because of the sweet nectar but do not eat or harm the flowers. Ignore the ants, or shake or brush them off before harvesting the flowers for indoor use.
How should I use Itoh peonies in the landscape?
As with most peony species, these plants make beautiful additions to cut flower arrangements. They are considered easy to grow, remarkably beautiful, and even have a fragrant lemon scent. They can often be found in perennial borders or mixed with other shrubs in hedges. Itoh peonies also work as a stand-alone specimen.
How was this peony developed?
Japanese botanist Toichi Itoh was the first to successfully cross a tree peony with a herbaceous peony in the 1940s. It was an extremely difficult process, as tree peonies and herbaceous peonies have different bloom periods, and finding a way to successfully cross-pollinate them took many years. The initial successes did not grow into viable flowering specimens for more than a decade. It was not until 1964 that the first-named cultivars were patented—years after Toichi Itoh passed away.
How long does an Itoh peony live?
Like other peonies, the Itoh is a very long-lived perennial. Some of the original breeding specimens are still alive, and 50-year-old plants are common.
How do I harvest the flowers?
Cut the stems before the flowers have opened, when the marble-sized buds still feel slightly hard. Place the stems in water and allow the flowers to gradually open. As you harvest, be sure to never reduce a plant's overall foliage by more than one-third.