The original root ball is in trouble. For recently planted plants of whatever kind, it's usually a matter of too little water in that region.

The only way to know for certain is to pull back the mulch to check the moisture stataus of the potting mix (or soil) which came with the peony.

I used a root stimulator when I planted it. Could I have burned it, and if so will it recover?

I think it is a mistake to plant a potted peony in the heat of summer, I would have kept it in the pot until fall. Your plant is stressed, it could be from the "root stimulator" or from the root ball not getting enough water. I do not recommend any root stimulators. Al

Think back to when you purchased it. If the plant was kept on a shaded bench the leaves were scalded by the sun. I have leaves that look like this if I forget to harden my vegetable plants in the spring before I plant. And when I water when temperatures are too high. With winter coming all to quickly the leaves will be replaced next spring so wait to spring to see how it does.

I think you are right, maifleur! It was in an area covered with a thin shade fabric, and I plopped it in the ground where it gets 8+ hours of full sun. How do you "harden" a plant, so that I don't do this again?

Calistoga: I thought I was helping the plant get established and prepare for winter. What is wrong with root stimulators?

By hardening you expose the plant to increased sun light and weather conditions.

An example is if you start plants indoors from seed. The plants are tender because all they know is the conditions of the room. If you immediately plant the seedlings outside they can get sunburn, wind damage, or go in to shock and stop growing. For most home gardeners can either place the plants outside in a shady location for several days or in some cases weeks moving them gradually to direct sun. Some place in a screened cold frame or on the north side of a stucture and bring the plants in at night.

I think that the plant was shaded enough that it did not get any direct sun and when you planted out at you altitude and the temperatures you had the combination of watering the plant and sun magafied the sun's rays causing the edges to burn. One reason I believe that this is what happened is the burned portion is where the water would congregate if watered from above. Also I have had similar damage on other plants like this.

When gardeners speak of root stimulators they are usually discribing some miracle chemical that does nothing beneficial and if anything is detrimental. If you are discribing inoculating your soil with mycorrhizal fungi then I would do it. Al

The bottle said Ferti*Lome Root Stimulator and Plant Starter. I used it on all of the perennials I planted that day, but the peony seems to be the only thing affected. Could it have been sick when I bought it? There were a couple of shoots that had been cut down to the base of the plant, and now I'm thinking that should have been a red flag. It was the only one in the color I wanted, so I was blind to any potential problems, LOL!

My guess is that the plant was suffering from botrytis and the affected foliage was removed because it was unsightly. The plant was weakened by the disease and this is the cause of your problem. I do not think the root stimulator was a contributor, nor do I think it was beneficial. Al

What is botrytis, and is there something I can do about it? Or is it fatal?