For any of you guys looking for cold-hardy zone 1 to 3 apples & crabapples - Check out this site link.
https[URL='https://www.uaf.edu/.../']://www.uaf.edu/.../HGA-00038.pdf. The University of Alaska -Fairbanks lists some apples & crabapples for fruit and --- for rootstocks --- Siberian crab, Columbia, Dolgo, Ranetka, or Red Splendor crabs. Some of the recommended apples are Prairie Magic, Carroll, Norland, Zestar, Yellow Transparent, Rescue, Lodi, Geneva Early, Kerr, Heyer #12, Hazen, Patterson. There are more on the list. I hope the reading helps you guys in your quest for some hardy trees.[/URL]