Prunus rootstock for zone 4

I have a bed of Myro rootstock that I use for grafting here in zone 7. I want to make some trees for upper zone 4, Fargo, ND. Most sources say it is good only in zone 5 and up but I have found a source that says good to zone 4. The late Dr. N.E. Hansen said Myro wasn’t good that far north but that was a hundred years ago. Can anyone give personal experiences of using it in zone 4?
Thanks in advance.

Fedco lists Myro as good up to Zone 3:
https://www.fedcoseeds.com/forms/fedco_trees_catalog_2018_highres.pdf (see page 16).

I expect that favourable reports on the coldhardiness of Myrobalan may be from places and periods that had reliable heavy snow cover, and maybe the trees were grafted low or planted with the graft buried. During the almost snowless test winter of 1980-81 I lived near Kingston, Ontario (E. end of Lake Ontario, Agriculture Canada zone 6a) and some Myrobalan seedling stocks were rootkilled.
There could also be variability; the book “Trees and Shrubs of the Dominion Arboretum” reports that a subspecies is hardy at Ottawa (AgCan z5a). For North Dakota I wouldn’t trust it.

dwoodard,
Thanks for the response. That’s a good idea to bury below the graft. Fargo is the wet side of the state but they can still get some snowless cold winters.

Anyone else had any experience?