My weather is coastal so a bit warmer than most...
HOWEVER, In coastal weather, temp fluxuates from below freezing, to 50+ n sunny, then torential downpoor then back to below freezing, all within a week! Perennials get VERY CONFUSED!
What I've learned is the importance of keeping them DORMANT until you are certain conditions will be CONSISTANTLY FAVORABLE. .(in the PNW, when the days start to get long enough to trigger plants to start growing again, we often get crazy/sudden COLD snaps-sometimes up thru MAY-that annihiliate perennials that became 'tricked' into thinking they had the 'all clear.')
DORMANCY will be a function of temperature, and more importantly, daylight hours - specifically NIGHT TIME HOURS.
Divide the peonies now and place them in 5+ gallon pots, with divisions close enough together that they help each other with heat, but not too close, as the tubers need room to grow and spread new roots while still potted (Cozy, not crowded).
If you have room in the ground, bury them in the pots. I dont have the room to bury in ground so i huddle them on side of house and surround them with stuff like bricks or plywood, patio furniture..anything to keep a consistant temp. They still get rained/snowed on, which is fine. But once the protective bud scales break open when the days get longer (BREAK DORMANCY-New growth begins), thats when I have to bring them into unheated garage on the cold snap days, or they risk death.
In other words, when daylight hours are long enough to trigger them to grow but you are not sure that the temp will stay consistantly COLD, then put them in the dark to keep them dormant.
If you opt for storing them in an unheated garage / shed, that's not a problem. But you will have to water them infrequently or they will dessicate and die. Remember, the roots are still respirating and need water, just a minimal amount.
Everyone's zone may be different, but we're all trying to 'trick' non-natives into performing in our climate. Hope this is helpful!
