Hi Ets7,
Welcome to the peony forum. I grow a few peonies in pots. I use ProMix BX amended with perlite and vermiculite. The key to success is excellent drainage.
Avoid potting soils that have fertilizer already mixed in. The ratios of NPK are not for peonies, but rather annuals. I use bulb food and azomite for peonies.
I have had success storing peony roots (they are not bulbs) in a cool room in my home until I'm able to
Plant them.
The problem with zone 7 is it doesn't stay cold the entire winter. You have to be proactive and protect your potted peonies from too much moisture that can freeze and thaw and cause root rot.
Good luck!
