I’ll also make some next week to see if the stage of development (how close to flowering, etc) is an important factor. I was just looking at last years grafting dates and take rates and I see that my earliest grafts on 4/10 (3 in 3) were followed by 76, 72, 63, 62, 61. Some of the other early success also had some 70’s,
Some of my (relative) failures in May (3 in 8 on the 8th) were followed by 56,61,59,60,51,67,67. Again- that fits the idea that you need 70’s for callus.
But, fast forward a few weeks and the grafts I made on the 23rd, 26th, and 28th are even worse (3 in 15). But the temps don’t look that bad: 68,58,75,71,68,57,60,71,78,74,72. Plenty of 70’s in there and not too hot yet. My thought is that I missed the initial growth flush.
The other counter example I am seeing is 4 in 5 on May 4th, when it had similar (cold) weather to the grafts on the 8th (which had declining results). 57, 65, 57, 56, 56, 61, 59.
The very preliminary hypothesis I’m drawing is that where you are relative to bloom/growth may matter more than the temperature. At least in my application. Looking at pictures from last year, peaches were in full bloom around 4/21. It would be nice to be able to say something like graft anytime between 1/4" green and 1.5 weeks after full bloom.
I didn’t record the state of the peach trees last April. But the first Japanese plum flowers had just started to open when I made the first peach grafts on 4/10. This year we are a bit behind that- no open JPlum flowers and the peaches are somewhere between green calyx and 1/4" green.
Two different peach trees in bloom last April: