I know you can graft like trees to like trees, but my question is: Can I graft an orange tree to a northern hardy root stock like a peach tree, and have it still grow and maybe produce an orange or two? I live in Buffalo, New York, USDA hardiness zone 6a.
Grafting compatibility depends on genetic similarity. Because of this, the most successful grafts are between species, within the genera. Inter-generic grafts are usually not successful, but in some cases where the genera are genetically similar, grafting is rather reliable (like the practice of grafting pear cultivars onto the hardier and more resilient quince rootstock). As far as I'm aware, no graft between families has ever been successful.
Because oranges are in the family Rutaceae, and peaches are in the family Rosaceae, the graft will not take. On another note, grafting a warm-climate scion onto a cold-hardy rootstock helps a little, but the scion will not be comparably hardy to the rootstock. For instance, navel oranges are often grafted onto Trifoliate Orange, Poncirus trifoliata (inter-generic), which is hardy to -20 degrees Fahrenheit, to improve hardiness on the orange trees. The trees are hardier than ungrafted trees, but not nearly so hardy as the rootstock.