A few tips on how to combat peony disease

Q. My peonies come up every year, flower and look beautiful. Then, the leaves turn ugly and brown. What can I do? Is it the plant or the soil? Should I replace them?

Darlene from Poland

A. It is the disease, not the plant or the soil! But the disease can survive in the soil to re-infect the plants next season.

You do not need to replace the plant or the soil. But if you see a quick collapse of the plant or lots of grey mold on the leaves, it is an option. Saying that, most of us just have spots on the leaves of our peonies – not a big deal, but unsightly from August until the end of the growing season.

This is due to the persistence of moisture in our garden environment.

Wet weather favors the diseases of peony that fit your description. Last year was a heavy disease year due to the higher-than-usual summer rainfall amounts. Thus, if you did not clean up the foliage from last year, you need to plan to combat the diseases.

Location & spacing: Some gardeners have peonies planted in the wrong place, many times because peonies live so long. Trees and other shrubs in the area eventually add shade. If this is the case, wait until September to move the plants to an area with full sun. You can also increase plant spacing at this time. Overcrowding is a common problem that increases disease pressure. When transplanting, keep peonies 3-4 feet apart for good air circulation.

Fungicides: There are many options for control of peony diseases; most are simply a preventative. Be sure to read and follow all label instructions.

Sanitation: No control option is better than sanitation. Some years, I end up cutting my peonies back to the ground in September. By that time, they’ve stored nearly all they can in their roots for next year’s growth. My disease pressure was so bad that I brushed back some soil and cut them slightly below ground. If you don’t have disease pressure, cut your peonies back to the ground after the first frost. Removing spent flowers after the last petals fall can also help, and will save needed energy in the roots.

To learn more about peony diseases, visit go.osu.edu/peonydiseases. For details on growing peonies, including cultivars, visit go.osu.edu/growpeonies.

Eric Barrett is OSU Extension educator for agriculture and natural resources in Mahoning County. Call the office hotline at 330-533-5538 to submit your questions. Regular clinic hours are Mondays and Wednesdays from 9 a.m.-noon.