Do you use weed & feed on your lawn? Since it appears only one side most effected any chemicals being sprayed in the area of the plant? Sometimes wind drifted chemicals can cause this. What amendments have you been adding?

I would be tempted to look along the stems for holes and to remove each of the effected leaves.

I don't remember what I tried for amendments - it was 10 years ago early in its life. It has always looked like this and it is really even all over the plant. It just looks like a nutritional deficency to me - I'm sure there has been some spraying on the the lawn but it does it so predicatably and all over the plant. Here's a couple pics this morning.

That first pic was deceiving and I think the variety in leaf color was from the lighting. (and the fact it was a cell phone shot one morning on my garden walkaround.. :)

I know I tried epsom salts that I use liberally around peonies, peppers, tomatoes, roses. I wonder if it is a pH problem causing absorbtion. My soil tends to a higher pH. I will have to test it again - haven't done that in a while. Overall it is lovely - the flowers were marvelous, but it has grown very slowly.

These are typical signs of iron deficiency (chlorosis). Apply iron supplements. I use Ironite Plus.

I agree and had done some further web searches - I bought a treatment for that today. Strange that I don't notice it on anything else in the garden, though - we'll see if it helps. Thank you!

You are welcome! For severe cases or for faster cure I apply liquid solution by spraying the foliage. If you will do this, avoid spraying it when the plant gets direct sun light.
Good luck!

It is hearsay but I have been hearing of gardeners with peonies of various types where the plants seem to be going down hill. Most of them really amended the soil before planting. I am wondering how wide spread the problem is?

Perhaps adding amendments to the area around the plants is a solution or only adding the bare minimum of amendments. Have you noticed any other plants that you may have planted at the same time struggling?

With my soil if I amend more than just a handful or two of compost I form pots in the soil. With the potting effect the roots will not spread into and down in the surrounding soil. This fall when the tree is dormant you might want to start at about 6-8 inches from the trunk and going outward remove a shallow trench as far out as you can to see if there is an abrupt change in soil. By now the amendments, in my brain, should have changed and merged with the surrounding soil.