A long-time friend and orchard owner sold me an apple tree that is supposed to be hardy to zone 2 (-50 F.). He gets most of his trees from Canada as he has an import license and Canada does much more research into cold hardy plants than we do. It has bee quite a number of years since it got to minus 50 F. here, it has happened. The tree is already blooming as it arrived in a shipment of 400 trees in a semi. It is still getting below freezing here at night, so we will be bringing the blooming tree in and out until everything stays above freezing consistently. No other trees are blooming or leafed out here yet, so if it didn't get pollinated in transit, it may be next year before we see fruit on it.
I don't know if the tree is self-fruitful or not. Even my orchardist friend isn't familiar with this apple, as apples are very rare in zone 2. Many apple trees require a second variety of apple to pollinate, although these northeren apples quite aoften are self-fruitful and can pollinate themselves. I may give it a try.