I have successfully grafted a few persimmons, but lately I've had poor luck. I had more luck when I grafted in late April, right when the first leaf came out complete. I waited this year until mid-May, and they don't seem to be taking. These were all American persimmons. When do you graft your persimmons? What makes them take more frequently? It could also be that they are older trees now.
I don't graft persimmons but as of the last 10 years my spring grafting experiences average between 1-2 dozen a year as you may know. So several years ago while grafting dormant scions into a same rootstock in the condition like this per coppicing; I tried three kinds of grafts. The whip & tongue, cleft, and (*iii) bark grafting in the slippery cambium area.
The rootstock was ferel chokecherry (prunus padus) in Alaska. The scions were a few sweet cherry and mostly plum and the reason is mostly the enjoyment of experimentation. It took weeks longer for the bark grafts to spring into action compared with the rest of them and bark grafted ones were not cold hardy survivors. So I have no idea if yours were bark grafted per *iii. So sometimes bark grafting just needs to be avoided. Hopefully others know more on the persimmons.
Mark Lee in the Seattle area at an event whom I've traded with before grafts persimmons. Somebody like him might read this some day and have a more accurate answer than mine. I know he has his own website.
Strangely, after two weeks, the grafts are starting to take. I thought it would have been sooner.
John, my belief based on some practice, and what I've read, is it is best after the tree has leafed out and when temperatures will be in the 70s and 80s for high temperature.
I missed the earlier windows so did mine last weekend. At the time the forecast for this week was 70s, but now its cooler. We'll see how I did. They weren't my most impressive grafts, but ones that certainly would take for apple/pear/quince.
They have been very gradually leafing out successfully over the last month or so. Jafar's hypothesis seems correct. Also, American persimmon may have a slower, or more delayed take than other fruit trees. It's hard to tell at this point, but it is an interesting data point.