I live in zone 5, and I have my callas in large containers. I let them dry when they begin to die back , which they do in about November, and bring them in and winter them dry in my upstairs room which is unheated and about 50-60 degrees F. About every other year I replace the soil. In spring I fertilize and water about now when they wake up. I move them in and out until frost is over, which is some work for sure. This has worked well for me for about 7 years. They've always come back. I even have some seedlings!

I am not sure you could really do it in the ground.

I'm in 5b as well. Most of my callas have corms while the aethiopica have rhizomes. Whether planted in the ground (most) or in pots I lift the corms after first frost.

Are you inquiring about lifting and storing over-wintering or hardiness for a z5b winter in the ground?