Lafayette County Master Gardeners: “Itoh Peonies”

The Lafayette County Master Gardeners are pleased to welcome the public to our Annual Spring Lecture Series which will be held in the Dotsy A. Fitts Auditorium of the Public Library on 401 Bramlett Boulevard. Parking is available at the library or across the street at the Oxford Skate Park. The lectures will be held at noon in the auditorium of the library. They are free and open to the public. The next lecture is Thursday April 4th, and the final lecture is Thursday May 2nd. Make sure you add these dates to your calendar. For more information or questions follow us on Instagram or Facebook, visit our website at http://www.lcmga.org  or call the MSU Extension office at 662-234-4451.

This is the third article in a series on Peonies (genus Paeoniaceae). We have covered two types of peonies: herbaceous and tree. Finally, we review the Itoh/intersectional peonies which are a hybrid of the herbaceous and tree peony and have short woody stems that die back to the ground in winter. This article will focus on Itoh peonies.

In 1948 Toichi Itoh, a Japanese peony lover, successfully made a peony cross that was thought to be impossible. Toichi had been trying for years to make the cross between an herbaceous peony (Paeonia lactifolia ‘Kakaden’) and woody tree peonies (Paeonia xlemoinei) with no success. It is reported that Itoh had created more than twenty thousand crossings of the two peonies. Towards the end of his life, he met with success in crossing a white-flowered herbaceous plant (P. lactifolia ‘Kakaden’) with pollen from a yellow-flowered woody plant (P. x lemoinei). Sadly, he passed away before the flower blossomed.

In 1966 Louis Smirnow, a New York accountant and peony enthusiast, secured the plants from Itoh’s widow and registered them in the United States as Itoh Smirnow hybrids. Soon American peony breeders were successful in their attempts to create the hybrid and introduced more selections to the market. These Itoh peonies were rare and costly due to the challenges in propagation. Costs for an Itoh began at $300 and could be as high as $1000 for a single plant. In the early 2000s a Canadian company, Plantek, began producing the peonies in tissue culture, making them readily available to the market. Today, Itoh hybrid peonies are still worth more than other peonies, but their inclusion in a garden is worth the price. They are available in big-box stores for as little as $20.

A mature intersectional peony will produce 50 or more dinner-plate sized flowers on strong short stems that do not require staking. They reach peak bloom near the end of the herbaceous peony bloom. Each plant can remain in bloom for 3–4 weeks, with new buds continually opening over this period.  Their compact form is well suited to the front of the perennial border. The Itoh hybrids have a finer foliage texture than herbaceous peonies and have better disease resistance. Itoh foliage remains attractive throughout the season. In early summer, you will be blessed with huge flowers (up to 8 inches across). Instead of disappearing completely below ground in winter, many intersectionals have inch-long, woody stems at the ground line. Stems tend to be stronger than their herbaceous cousins, presenting the flower beautifully above the foliage.

When choosing a site, first consider the amount of sun. The more sun, the more flowers the peony will produce. If planted in less than full sun, it will take longer to mature and won’t produce as many flowers. Second, peonies need rich soil, good drainage, and a neutral pH. You are looking to create a sandy loam—soil with equal parts sand, clay, and compost. Soil testing is recommended and can be submitted at our local extension office. Directions for collection and submitting a soil sample can be found here or by searching “soil sample” on our website at https://extension.msstate.edu/. They cannot tolerate wet feet. Do not plant in low-lying areas that retain water and be cautious when planting close to automatic sprinkler or irrigation systems. Be sure to follow the directions for your specific type of Itoh peony and allow adequate spacing for air circulation to minimize fungal disease. New intersectional peony plants should be planted 3 to 4 feet apart from the center, and approximately 1.5 feet from any edge or border. Think long-term when you are laying out your peony garden; they will take about three years to mature and will live happily with minimal care for decades. When using intersectional peonies with herbaceous peonies place the intersectional peonies in front. This is a great way to extend your peony bloom as the intersectional peonies will continue to flower after your herbaceous peonies have faded.

Peonies can be planted in spring, fall or winter. Spring planting occurs from the time the ground starts to thaw, through mid-June. They should be planted as soon as you can get a shovel in the ground, regardless of the last frost date. It is best to plant them while you still have cold or snowy days in the forecast. If you are planting bare-root Itoh peonies in spring, it is likely that your peonies will produce minimal growth above ground the first year. If you are planting peonies that have been grown in pots, there is potential that the buds will wither and the leaves will die back early. Don’t worry, this is normal. To plant, start by digging a hole one-foot-deep and one and a half feet in diameter. Amend your soil, as indicated on your soil sample results. In zones 7 and 8, your red peony buds should lie one half inch below the soil. Planted too deeply, flowers will not develop; too shallowly, and the tops of the eyes will freeze, dry out, and die. Press down on the soil to remove air pockets around the root and lift the root as necessary to ensure proper depth. Water in well, then again ensure proper depth. During the first growing season after planting, ensure that your peony gets a good soak every two to three weeks. To thrive in your garden, it must get this thorough soaking—without it, the peony’s fibrous roots will not establish themselves, and it won’t be able to absorb proper nutrients. Typically, rain is enough; however, in times of drought, in exceptionally hot weather, or if your peonies are planted in sandy soils, consider watering more frequently. Avoid overwatering, as too much water will invite both root rot and disease. We do not recommend planting peonies near automated watering systems.

When maintaining your Itoh peonies, you do not need to stake them. Once flowers are spent, remove the dead flower heads. Plants will not produce viable seeds so there is no need to keep them. It is best to focus the plants’ energy on leaf and root development. Intersectional peonies can tolerate more heat than herbaceous peonies and can grow all the way south to Horticultural Zone 9. No additional care is recommended or required for these types of peonies in Oxford, zones 7. Feed lightly three times a year—in the fall when you clean up your garden and prepare plants for winter, in early spring just as shoots emerge, and again in early summer after plants have bloomed. Peonies like heavy infrequent soakings; when irrigation is necessary avoid sprinklers and overhead watering. Established peonies require less supplemental watering but still benefit from heavy infrequent soakings, especially in times of drought. Remove leaves in fall and trim leaving woody growth intact. Do not mulch your intersectional peonies! Mulch will bury the crown of the peony too deeply and eventually cause it not to flower. In transitioning away from using mulch, remember that light layers of compost applied regularly around the drip line of your peonies (not on the crown) will feed your garden and can also help suppress weeds. The shade from mature peonies will act as a weed suppressant from late spring to late fall. The first application of compost in early spring helps combat weed growth. Consider under-planting your peonies with small spring bulbs, like miniature daffodils and crocus. They bloom before peonies, don’t compete with them, and provide a nice early summer groundcover that reduces weeds. Be careful not to plant anything larger or that is particularly invasive around your peonies, or anything that will compete with your peonies and cause them to suffer. Do not use weed suppressants anywhere close to your peonies! If you anticipate a hard or prolonged frost after your peonies have sprouted, you can protect your plants by covering them. Make sure the covering does not touch the plants or you will do more harm than good. Do not touch your peonies when they are frozen as this will cause them to break, wait until after they have warmed up.

Intersectional peonies have flowers that look like their tree peony parent but have longer stems, like their herbaceous parent. Be careful when cutting the stem, as it is important not to cut the woody portion of the plant that will remain above ground. It is also important not to take more than a third of the leaves at any given time, so be careful when cutting multiple stems. Intersectional peonies make outstanding cut flowers in colors that are not often found in peonies. If you are worried about ants when bringing cut flowers into the house, simply cut the flowers when the buds are still closed, making the ants easy to shake off. Also, if you cut your flowers in the early morning or evening, there are often fewer ants on the buds.

Peonies are very resilient plants that typically thrive and grow without incident. However, every once in a while, a fungus or virus may take hold and impact the health of your peony plants. Although infections generally start in early spring, they often go unnoticed until later in the summer. Left unchecked, these diseases can do real damage to your peonies. If you are experiencing a white, powder-like covering on the leaves of your peony, you have powdery mildew in your garden. The leaves will seem to be covered in a white substance. Generally noted in late June through September. In some years, powdery mildew is worse than others. It can infect plants when there are hot days, high humidity, and cool nights. Once the plant is infected there are virtually no sprays or oils that will completely rid the plant of powdery mildew this year. However, there are some preventative remedies to keep your plants from getting powdery mildew in coming years. Bacillus subtilis can be used to boost plant’s natural defenses; neem oil or other horticultural oils after the leaves have formed; baking soda spray (1t baking soda, 1qt. water and a few drops of liquid soap) on the soil in early spring and on the plant itself in the summer; rhubarb leaf tea; cornmeal as a soil amendment; or mixed as a spray; products containing sulfur, or a biofungicide recommended to treat powdery mildew on peonies. All pesticides should be used according to package directions, and remedies should be tried on portions of the plant prior to making large scale applications.

Botrytis causes Itoh peony stalks to wilt, then die and buds turn black. Onset is typically in early spring but can be at any time when temperatures remain below 70 degrees. Botrytis is especially prevalent when the weather is cool, wet, and humid. Botrytis is common and when seen in your garden can persist for years through spores in the soil. Botrytis is easy to treat but can kill peonies and other plants when not treated, so it is especially important to pay attention to signs of the fungus. When noticed, cut off diseased portions of the plant, dipping the pruners in a 10% solution of bleach (or use Clorox wipes) between each cut to ensure the disease does not spread. Throw out the diseased portions; do not compost. A more aggressive option would be to use systemic fungicide labeled for use on peonies. Follow label instructions carefully and test fungicides on one plant before making large scale applications. Continue to treat according to the label instructions as the disease persists.

Phytophthora Blight (Phytophthora cactorum (Fungus) is a soil-borne fungus. The stems at the base of the plant will begin to darken and then wilt and die. Leaves may appear drought stressed. The entire plant may rot making it easy to pull from the ground. The fungus can survive in the soil for years as long as moist conditions persist. It can be spread by garden tools and contaminated soil. Symptoms are often more evident during periods of low rainfall making it easy to confuse the onset of this disease with drought. Phytophthora can kill peonies and other plants. When noticed, cut off diseased portions of the plant, cleaning pruners between each cut to ensure the disease does not spread. Clean up all debris around the plants and discard – do not compost.  Subdue (fungiside) can be used to treat Phytophthora on peonies, apply according to the manufacturer’s instructions. Be sure to treat both the plant and the soil. Improve soil drainage and prevent water from pooling near plants.

Sclerotinia Rot is a soil-borne fungus. Rot begins at the base of the plant with water-soaked stem lesions.  Leaves will turn yellow and die. During times of high humidity, a white cotton-like fungus spreads around the base of the plant and the soil. The fungal fruiting bodies appear like small collections of mustard seeds on the ground near the base of the plant. They may eventually form a crust on the soil. Sclerotina can kill peonies and other plants. Rutgers Diagnostic Lab recommends using either Heritage or Headway for use on peonies for Sclerotina Rot, apply according to manufacturer’s directions. Be sure to treat both the plant and the soil. If that fails, remove diseased plants and the surrounding soil from your garden, do not compost. Sterilize all tools. Cover the area with clear plastic and leave it for two to three months in the heat of summer. After this period, increase the drainage in your soil and leave the soil fallow for at least one season before replanting.

Peonies are also susceptible to a small number of viruses including peony ringspot virus, leaf curl, Le Moine disease, and the mosaic virus. These are rare, difficult to cure, and it is generally recommended to remove infected plants from your garden. You will see poor growth and stunted growth. Leaves will have a mottled/mosaic appearance. Portions of the leaves can turn yellow and die. Can be spread by insects or tools. Viral diseases can kill peonies and other plants. Remove and dispose of infected plants, do not compost.

A wide variety of stressors can prevent peony buds from opening (also known as Bud-Blast). This can include poor soil, immature plants, plants being buried too deeply, excessive mulch, not enough sun, and early spring frosts. Check the depth of your peony and adjust if necessary. If you notice your Peony flowers being eaten look for Chafer beetles which look like Japanese beetles. They can be removed by hand or killed with almost any insecticide. Neem oil is an organic option, read the product label for more detailed instructions. Ants are natural predators and chase away chafer beetles.

If the overall health of your plant is declining, check planting depth, the amount of water, competition of roots, depletion of nutrients in the soil, or note if the area has flooded recently. It may be time to transplant your peony to a new location. Wet soil is a common factor in unhealthy peonies. It is possible to divide your peony when you transplant it by following instructions below. Plant divided roots in a new section of the garden so the soil in the former location can recover.

When dividing an intersectional peony, wash the dirt off the roots. The root has four parts: large tuberous roots, small fibrous roots, a connective crown, and eyes at the top of the crown. Rinse off the peony so you can see the plant clearly. Divide the plant into pieces by carefully cutting through the crown. Each piece should have at least one strong tuberous root and 3-5 eyes on the top of the crown. Plant each intersectional peony 3 feet apart.

If peonies are your passion, consider attending the 2024 American Peony Society Convention in Bloomington, Minnesota on June 5, 6, 7, 8, 9. For more information, see the American Peony Society Webpage or select here. The APS also uses peony auctions for fundraising. If you have a plethora of peonies, reach out to share your abundance with the APS for a good cause.

References:

American Peony Society 
Clemson College of Agriculture, Forestry, and Life Sciences
University of Arkansas
Rutgers Diagnostic Lab
P1826 Annual and Perennial Flowers for MS Gardens or search for P1826 at https://extension.msstate.edu/