they can survive in the ground in my zone with temps in the 20's but that is with an insulating soil cover. containers don't provide that.
i would move it inside before mid-20's are expected.
as an example, i lost a large, established in-ground one years ago when it dropped to 18 degrees. others that i grow have survived short duration mid-to-upper 20's in successive winters.

Thanks Jeff

I bring mine in when it hits 40F. Anything colder, and it could freeze, especially when in a container.
Another reason is, when kept cold for long periods, it seems some plants are more prone to leaf drop, especially if brought inside, in a warm house. If possible, do it gradually. When days are 50's and 60's, keep outside, but when night temps drop below 45F, bring inside. Do this a week or two. Or if you have a cool room, do it at once. Good luck, Toni