Hello CA_Poppy, and the rest of the people on the forum.
Before answering I have to apologize for my long absence from the forum, since I have been convalescing from a knee prosthesis intervention that has had me completely inoperative for a few months.
Well, now we return to the subject since I have extensive experience with cherry trees.
As long as the size of the rootstock allows it, without a doubt the best grafting system in cherry is the whip and tongue system, since the union is perfect, unlike other systems such as cleft graft that in cherry makes very bad unions. generating bulging at the graft point and generally ending in breaks caused by the wind.
The whip and tongue graft in cherry should be done at the end of winter, and the best time is just before the rootstock enters a vegetative state, it can also be done in early spring when the rootstock is entering a vegetative state, but it is much better to do it in those 10 or 15 days just before the rootstock enters a vegetative state.
If the diameter of the rootstock is too large, throughout the spring and with the rootstock in a vegetative state, the Chip Budding graft can be used, which also offers very good results and makes perfect unions.
It also very well the bud grafts in T.
But as I mentioned, do not use the cleft graft system, since in cherry it is not recommended.
When they are adult trees of great diameter, and what is intended is a change of variety, the system used is the crown graft.
If you have any questions you can ask me and I will solve all your questions
regards
Jose