More cold-hardy than southern pecans, Northern Pecan (Carya illinoinensis) have been successfully overwintering on our farm going on 4 years now. In fact, they have proven to be more cold hardy than english walnuts.
These seedlings are 8 to 16 inches tall, 2 year old, bare root.
Photo credit: Pmg, CC BY-SA 3.0 <http://creativecommons.org/licenses/by-sa/3.0/>, via Wikimedia Commons