We’ve had similar experiences in Southern Kansas and have less vigorous winters than you. We have 3 14’ tall trees behind the house now, I started the process the spring of ‘14 with seeds I bought online. Our trees are a little behind, I neglected to prune them appropriately when they were smaller, so the pruning we’ve done over the last 2 years has slowed them some im sure. We’ll have to prune some more next year, then they should be good to go. Every time I look at those 3 trees, it’s worth the process. Still haven’t produced any nuts, maybe this is the year? I’m gonna have to spray them again this year, the ants love the leaves. I was hoping natural predators would take care of the ants, but they’re failing so far.