These are the four points of balance that make grafts fail: too wet, too dry, too warm, too cool.
Grafting takes three steps, callous on the scion, callous on the host, and then the callous fusing. The balance is different for every life, but for healing to take place, it needs to be warm enough to callous but not warm enough to dry the scion or flood the graft (certain trees), moist enough to sustain the scion but not wet enough to mold or rot.
Grafts fail when callous does not form or the callous is not in solid enough contact with the host long enough to fuse before the outer layer of the callous dries out and dies. Temperature is temperature OF THE GRAFT SITE. Heating or cooling IS effective (ie wrapping in black).
FOR APPLES/PEARS: Callous temperature between 40 and 65ish, callous dries slowly. WILL callous in cold storage.
FOR PEACHES/PLUMS: Callous temperature between 60 and 80, callous dries and rots quickly.
FOR FIGS: Callous?? They will callous at room temperature, which is how people root them. They flood easily, apparently.
FOR POMEGRANATES: I don’t know