Yard and Garden: Peonies

The garden peony is a popular, long-lived perennial that provides abundant flowers in spring and attractive foliage throughout the growing season. If given a good site and proper care, an established peony will flower for many years. Common peony questions are answered by Iowa State University Extension and Outreach horticulture specialists. To have additional gardening questions answered contact the specialists by calling or emailing the ISU Extension and Outreach horticulture hotline at 515-294-3108 or hortline@iastate.edu.

My peonies bloom poorly. What could be wrong?

There are several factors which may cause peonies to bloom poorly. Peonies perform best in areas that receive at least six hours of direct sun each day. Peonies that receive less than four hours of direct sun will not bloom well. Plants growing in a shady location should be transplanted to a sunny site in September.

Peonies planted too deeply often fail to bloom well. When planting peonies, position the peony buds 1 to 2 inches below the soil surface. Peonies that are planted too deeply produce lush foliage, but don’t bloom well. Recently planted or divided peonies may not bloom well for two or three years. The new plants need to grow stronger before they are capable of blooming well. Also, premature removal of peony foliage in July or August weakens plants, resulting in few flowers the following spring.

Flower buds form on my peonies, but don’t open. Why?

There are several possible explanations why peony buds fail to open.

Peonies bloom best in full sun. In partial to heavy shade, plants are weak and may not be able to supply adequate food to the developing buds. As a result, the undernourished buds don’t develop fully. Peonies growing in partial to heavy shade should be transplanted to a sunny site in September.

Fungal diseases, such as Botrytis blight, may infect peony buds. Infected buds turn brownish black and wither. Fungal diseases are most common during cool, wet, spring weather. Sanitation is the most effective means of controlling Botrytis blight and other peony diseases. Cut off peony foliage at ground level in fall. Remove the diseased plant debris from the area and destroy it.

The flower buds may have been damaged by freezing temperatures in spring. While peony plants can tolerate temperatures in the upper twenties or low thirties, the flower buds on peonies are more susceptible to cold injury. Unfortunately, little can be done to avoid this problem.

Are ants necessary for peonies to flower?

Ants aren’t necessary for peonies to flower. The ants are attracted to the sugary nectar produced by the peony buds. The nectar is a good food source for the ants. Peony buds will open without the presence of ants.

Should I remove the spent flowers on my peonies?

It’s advisable to remove the spent flowers on peonies. Removing the spent flowers (deadheading) improves the plant’s appearance and prevents the formation of seed pods. Seed pod development reduces the amount of food the plant is able to store in its root system and may result in fewer flowers the following spring.