The best thing to do is to buy peonies that don't flop in the rain. Hollingsworth Peonies calls them Landscape Worthy or something like that. However, if you do have some that flop, I prefer to use grow through rings to peony rings. I think it gives the plant more support.
http://www.gardeners.com/Grow-...
There are lots of ways to stake peonies. The above is just the one I use the most often.
