Despite their name, Calla Lilies are not Lilies and it is a wrong forum to ask questions about them. You can find tons of useful info on 'Aroids' forum.

I am in a similar zone. I grow Callas both in pots and in the ground. You should lift them after the first frost and store inside for the next season. Last year, I planted a couple of Callas next to the house foundation (about 2' from it). I did not dig them up for this winter. They overwintered successfully.
The soil should be extremely well drained. Soggy soil will kill them in no time.
I use Espoma Bulb-tone for fertilizing Callas. Some bone meal at the planting time.
Good luck!