Planting two or more trees in the same hole is common and has some advantages versus multigrafting. It’s commonly done for pollination partners. But what about for soil adaptability? Something I’ve been thinking about is pair planting peach and plum. Plum is supposed to be more adaptable to soil type because the roots can secrete acid to acidify the soil, whereas peach cannot. If I was to pair plant peach and plum, or graft peach to a plum rootstock, should I expect a more adaptable peach / less problems with root rot?
I don’t like the idea of mixing two different rootstocks in the same hole. Competition can be problematic. I would either multigraft one stock or use a pair of identical clonal roots for both trees.
Some peach compatible plum rootstocks are certainly well adapted for flood irrigation conditions and high pH calcareous soils.