Most cannas are supposedly hardy to zone 7b, and I'm supposedly 7a, but I have a really warm microclimate in my backyard. Southern full-sun exposure, brick wall, protected from wind, and on a slope so doesn't stay wet.
This is my first year growing cannas (they were from you!
) so I was going to leave half in the ground and dig out half to experiment. In my immediate area, everyone I know leaves them in the ground.