I had heard that there was a collector of tree peonies in Studio City - all in containers. So if that's true it means it can be done. Good luck! I have a few of them I put into the ground and two I gave to my mother in pots - we'll see what comes back in the spring (first year for them).

I have a question for the op, have you had any success yet? I am also interested in growing them too in pots here.

Considering the eventual size of 3 to 4 feet high and wide, I would go for a pot size of 18 to 24 inches. Soil would be based on ground fir bark, sand and volcanic rock for the longest lasting container soil. An east exposure in socal would be best. Chilling will not be a problem with tree peonies. Al

My MIL planted one and it is doing fairly well after 3 years and has bloomed twice. Morning sun, afternoon shade.

In zone 10, choose the early-blooming peony varieties. In this climate they need to be planted in partial shade, and consistently watered in the Summer. The bud tips need to all be cut off in October to help the plant go into dormancy.

Itoh peonies are said to do much better than others here, possibly because they are very early blooming and have an extended blooming period.