Are Montmorency Pie Cherry trees grafted? If so, what root stock is most commonly used?
Yes, many are. The rootstock, seems to be Gisela 5 these days. Mine is an eight year old tree on Mahaleb. It is a dwarfing but precocious rootstock. The tree is very healthy. I am purchasing another sour cherry for next spring and it will be on Gisela 5.