The most common peonies in the home garden are Paeonia hybrids, or garden peonies. These peonies grow 2 to 4 feet tall and are thrive in USDA Plant Hardiness Zones 10 to 2, making them perfect for growth in Ohio, whose northern half sits in Zone 5 and whose southern half sits in Zone 6. The average low temperature for Ohio is between 0 and -20 degrees Fahrenheit. Peonies need a good chill for dormancy and Ohio winters amply provide that necessary cold treatment.
Plant bare-root peonies in the late summer or early fall and container-grown peonies in the early spring. Plant bare-root peonies so the eyes—the small, red-colored buds along the roots—are 1 to 2 inches below the soil surface, but no deeper than 2 inches. Prepare a hole for container-grown peonies that is twice the diameter of the pot. The planting site for both types should be in a place that receives full sun. Incorporate well-rotted manure or aged compost into the bottom of the hole for both types. Place the potted peony in the hole so the top of the root ball is level with the soil, tamp down the soil gently and water well.
Plant, divide and transplant peonies in early fall for best results, but early spring will suffice as long as the soil is workable. Peonies require at least 3 feet between each plant. This will allow ample sunlight to access the shrub and proper air circulation to prevent fungal diseases that tend to attack peonies during wet springs.
Soil and Soil Amendments
If you are planting peonies in a bed that has never before been used for growing perennial plants, amend the soil so it allows your peonies to absorb the maximum amount of nutrients. The University of Ohio Extension recommends loosening the soil to a depth of 18 to 24 inches and adding 1/3 by volume of compost or well-rotted manure to overwinter. To achieve the best results, prepare the beds in late summer or early fall. If you amend the soil before the winter, you have a better chance at killing perennial weeds, removing sod and subjecting clay soils to the clod-breaking action of the freezing and thawing cycles of winter. Gypsum, the Extension advises, does not work as a soil softener in Ohio.
Peonies will be happy for years without being moved, but if you notice your peonies flowering less, the plants would probably benefit from division. Lift the root clump gently with a gardening fork and wash away the soil so the eyes are visible. Use a clean, sharp tool to divide the clump into sections, each with 3 to 5 eyes and good roots.
Cut peony stems back to 1 or 2 inches above the soil line after the first killing frost. Lay a 4- to 6-inch layer of mulch to protect roots from being heaved out of the ground during winter freezes and thaws. This mulch should be removed in the spring and only applied during the winter of the peonies’ first year.