Did you plant your peony from a container without disturbing the roots? The feeder roots are too small for you to see and if those need to be grown the plant will suffer until they do. Since you have it dug up I would sprinkle Mycorrhizal fungi on the roots before replanting.You can find it at nurseries under different trade names read the ingredient list on the bottle. This will help the growth of the feeder roots you are missing. Al

I'll try it. When I planted it, the container soil was very, very loose, even though it was appropriately damp. It simply fell from the larger roots, and I guess I don't know what the soil took with it.

Wouldn't it be a good idea to transplant it to a spot with more shade, so it will have less environmental stress?

Al, were you going to say, I should not have not dug it up? I really don't understand why, if the problem were the feeder roots, why the wilting and stressed leaves didn't show up for a month.

Thanks,
Marie