I planted my seeds this fall in 3 gallon pots. I cut the bottoms out and planted the pots in my front garden where I've had volunteer peonies come up from seed where I neglected deadheading. Haven't seen anything yet, of course, probably won't next spring, either. I think the pot thing will work well just because you won't forget what's planted where!

Another option might be something like winter sowing.

I don't see why you shouldn't start them in pots. I haven't had any luck with tree peonies, but have started herbaceous peonies in small pots. I'm planning on transferring them to a propagating bed and letting them grow until they're big enough to go out in the garden.
Melissa
P.S. My answer wasn't quite to the point. I've not only started peonies in pots, but grown them there for a year or more, when I wanted to get size on a plant before putting it out. I don't know why you shouldn't grow them in pots. If you live in a cold climate I expect you know you need to protect plants in pots in the winter.
Peony seeds that aren't fresh can take a long time to germinate. I've had some sprout a year after I planted them; others germinated the first year.

This post was edited by melissa_thefarm on Mon, Oct 13, 14 at 10:12