We had to cut one back a couple of winters ago when it got badly damaged by the weather. We cut it back severely to just above the ground and it quickly grew back to its full size though it is rather 'looser' now than previously. I would suggest that the stems are still a bit sappy and would leave it until December/January.

I have 3 tree Ponies Celiamaud but I never cut them back.

One is in its 6th year and 2 are in 1st year.

I take off the spent leaves but never cut back.

How ever the peonie roses I cut back toground.

Me others will tell you different but this works well for me.

I was given advice from the RHS to cut my large tree peony back in February and to do this over 2 years. I did the first prune last year, cutting back to just above a bud, and it flowered well, so I shall prune again this February. My tree peony is about 7 years old.