Mulch for Peonies
In most gardens, mulch is a good idea. Bare soil around your plants invites weeds and erosion. Bare soil dries out quickly. Bare soil is part of the life cycle of some plant diseases that count on being able to splash back up onto leaves.
So it seems obvious that you'd mulch around your peony plants. Still, you will hear conflicting advice. Why?
In their early growing stages, peony plants are susceptible to Botrytis cinerea, or gray mold. Anything that damages plant tissue, such as a late freeze or an errant soccer ball, can invite Botrytis to set up shop. Other plant diseases and pests are few for peonies, but Botrytis can be serious.
The no-mulch theory states that the drier you can keep the area around your plant, the less likely Botrytis is to be able to survive in the soil and reinfect it. Mulch retains moisture, and in this theory, harbors Botrytis.
Where I live and farm, keeping the soil surface dry isn't really a viable strategy. Here it rains much and often. Botrytis spores in the soil have ample opportunity to splash right up onto my peony leaves. Mulching actually reduces rain splashing. There's too much surface area for the water to get a good bounce.
What I've found on my farm is that peonies that are growing in or near mulch are healthier and more able to withstand disease on their own. So I plant my roots in high ridges with furrows between to drain away excess rainwater, and I mulch with wood chips. They scatter the raindrops, keep the soil cool in my hot summers, and improve the soil as they decompose. I'm definitely on the pro-mulch team.
But a few cautions before you mulch. When we planted your peony, remember how careful we were about the soil depth over the eyes? Don't ruin that now by covering the crown and eyes up with inches of insulating mulch. Place your mulch in a ring around the plant, keeping it away from the stems.
If you do have a bad problem with Botrytis one year, you'll need to remove the mulch, cut the stems back when they wither in the fall, and dispose of stems and mulch in the garbage. Don't compost them, as the spores can survive and cause trouble again. Replacing the mulch with a fresh layer will give you a fresh start.
My understanding of mulch and the ways it interacts with the soil and peony plants in particular is growing and evolving along with my farm. I know there are those who say peonies hate mulch. But my ladies seem to love it.