Name: Susan Virginia (Zone 8a) God is the only thing that matters.
Wow, I could run with that.
Consider the lilies of the field, how they grow; they toil not, neither do they spin: And yet I say unto you, That even Solomon in all his glory was not arrayed like one of these. Mat.6:28-29
I think the rule of thumb is something that is hardy one or two zones colder should winter in a pot in your area.
e.g. A zone 4 plant is safe to winter in a pot in zone 6, and a zone 5 plant might be OK.