I wouldn't feed it anything.

I would snip off any dead or dying leaves.

I would drape some sort of shade device over them until they recover.

When they suffer from high temps and low water they sorta shut down anyway, so they should be dormant. By shading them a bit, keeping them just damp (not soaking wet) and maybe consider giving them a pruning you will encourage some new growth.

Tree peonies are tricky and not the easiest things to grow here.

I have three tree peonies and this is normal behavior for them this time of year. The leaves turn black. Two of the peonies are 35 yo.
I do nothing. It is just part of the cycle of the shrub.

Jim
Hillsborough,NC

I agree with the above advice. I've lost more tree peonies to overwatering in summer than for any other reason, so don't resort to that, and definitely don't feed them right now. Just let them be dormant at this point. I wouldn't provide any extra watering for them during vacations, either; I make sure that mine are well out of the paths of sprinklers during the summer, as well. They're hill and mountain plants in Asia, used to dry soil, perfect drainage and a short growing season, so they're not designed to hold (or need) their foliage for as long as our growing seasons last. I've managed to stave off the foliar damage in the past by regular applications of fungicide, but have decided that it's not worth the effort in the long run. It doesn't seem to affect their performance one way or the other during the next growing season.

The posters description matches what is going on with my regular peonies but my tree peonies are showing no signs of summer stress. In fact they usually don't start with the browning leaf edges until much later in the year for me. I only have the purple ones which seem to do better in this area but they need some shade during the heat of the day (opposite of what the normal advice is for tree peonies).

Yep- i concur with John- my regular peonies often turn black and lose leaves prematurely, but come roaring back the next year, and sometimes the tree peonies do as well. Mine looks a-ok right now this year, though. I also have the purple one and it only gets a few hours of direct afternoon sunlight, so maybe that helps. I wouldn't worry to much about it.

herbaceous peonies and tree peonies are two different animals all together. My tree peonies are in full sun and flourish. Again, two of them are thirty-five years (or more) in age. Some varieties may be more 'shade needy', like the Japanese hybrids, but that would be a question for the peony forum from people who have had first hand knowledge of particular cultivars.