I don't know much about ivy, but I do have a potted variegated Hedera canariensis that's been outside for 8 yrs. It was on the back porch of the house I rented. The lowest temp I'm aware of in that time was 9 degrees. I never do anything to it but wind the long stems back up the arms of the hanging pot when they get long, a couple times per year. For the past 4-5 yrs, it's been hanging in a tree at my Mom's house. Better to be safe than sorry though, if there's any uncertainty (and you would be upset if your plant didn't make it.) If you get a 2nd pot of it going, you could experiment with 1 next winter.
