actually rooting hormone can increase the success of the graft. It increases the formation of callus and the rate at which the new cambium cylinder is differentiated through the callus parenchyma cells. Cell division is increased etc. At least it does work in trees and I don't really see why it wouldn't work in herbs. In the youtube video I linked to he mentions, yes, he did use rooting hormone. My understanding is that powder based works best, but liquid has success as well.