More cold-hardy than southern pecans, Northern Pecan (Carya illinoinensis) have been successfully overwintering on our farm going on 6 years now. In fact, we've found them to be cold hardier and more adapted to our environment than english walnuts.
These seedlings are 3rd year, 10 to 18 inches tall, bare root.
Photo credit: Pmg, CC BY-SA 3.0 <http://creativecommons.org/licenses/by-sa/3.0/>, via Wikimedia Commons