Peonies need a rich soil.
When I transplant mine, they will be able to ingest the bacteria and castings from a bag of well rotted manure. I'll even throw in some grounds and shells..
Lots of digging and work, and I may be overdoing things.
This is my thought of the day.

Besides good soil and enough water, good air circulation is required to keep the foliage free of fungus diseases. The non developing buds I think will be eliminated with the health of the plant improved. Fungus diseases can only be avoided not cured. A good fungicide can limit further infestation, but does nothing for the damage already done. Al

As soon as you feel the leaves are no longer supplying energy to the plant, cut them completely to the ground, clear all debris from the rootzone, topdress with milled sphagnum peat moss. I do this every spring and fall for all my peonies. I originally got this idea from a related idea of using milled sphagnum moss as a top dressing in cells to prevent damping off, I figured if it stopped the fungal disease of damping off it ought to work on the fungus on my peonies, right? It was so bad on mine that they didn't even bloom in the spring, they would get buds that would turn black and die. The first year I did this I got a few buds to open. The second year, most of the buds opened and the leaves lasted until August. Now I even get fall color from a few of them. I still get some black spots, especially if there is alot of rain, but I just trim them back when I find them and keep up my routine. Hope that helps.

Jeanne

Here in Denmark it is not recommended to lay sphagnum moss around peonies. Au contraire, it is considered to be better to use gravel around the stems or coarse sand(something that dries up quickly)

Here in California we do not cut down peonies until frost which is usually sometime in November for lower elevations. Mulch is never added on top of the roots as the added insulation will limit winter chilling. Al

Thanks to all who provided experience. I am now using fungicide as a preventive. The mildew has not yet appeared.

As far as the buds turning brown and failing to open, I was told years ago to spray them in the spring with something called (I think) Benedryl (or a name something like that--bene- something). It worked for the first few years after I planted my peonies. Then I ran out and never got around to buying any more. However, turned out I no longer needed it. When my peonies got more mature--let's say, 5-6 years old--the buds quit turning brown on their own. An occasional bud might still do it, but most of the buds did what they are supposed to do: bloom. Now that I have had most of the peonies in the ground for 15-20-25 years, they do their own thing without my help, to a great extent.

However, I too have had problems with the leaves getting big splotches of brown as the summer wears on and gets hotter and hotter. I don't know how to treat that--because I don't know what it is. So I will be interested in any ideas any of you can share on solving that problem.

Thanks,

Kate