I suspect late frosts have killed my scions the last two years. I usually have painted the whole scion with tree kote. Is that regular parafilm you are using?
Any other ideas for late frost protection?
Last year I put a sheet rock screw in some of the bark grafts to hold it tight. Seemed to work.
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I don't have late frost issues with persimmons. By the time they leaf out, the sap is running well, and the bark is slipping, it is usually around May 10th (here in zone 7a). Our 10% chance of frost date is April 15th. As I said, I haven't done any bark grafting of apples in the field and that could be a problem for apples as some varieties do green up much earlier than persimmons. So, I don't have any solutions for late frost.
As for the parafilm, there seem to be quite a few differences in it. I bought some from a grafting supply place. It is thick with very little stretch to it. Buds seem to have difficulty pushing through it. It does not break down easily and I don't use it for much any more.
The stuff I use to protect scions is called Parafilm-M. It is used in labs to seal beakers and such. The smallest width I've found is 2". I simply cut it to the width I need given the application. It is significantly different. You can stretch it and it get thinner and adheres to itself well. Buds break through it easily and it breaks down in the field so you don't need to remove it. Unlike the other stuff, it will not girdle a scion. It keeps the scion from drying out.
As far as the sheet rock screw goes, it might depend on the tree. I do know with hardwood trees like pecan/hickory, it is common to use a staple gun to attached the scion to the tree. They use pretty large scions for that, many as thick as my thumb. They also use an interesting technique where they shellac to keep the scion from drying out. I've done it when grafting pecan to hickory. My results from that were so poor I stopped but that is more likely compatibility issues rather than bark grafting technique. I only had a 30% take and tried several bark grafting methods. Successful takes were more related to the specific kind of hickory rather than the technique I used to bark graft. I have not tried either of these things with persimmons.
Another tip for the OP:
In addition to the normal angular scion cut on the side of the scion that goes against the tree, I list to make a fine angular cut on the back side about 1/4". The cut is made at such a slight angle that it mostly remove bark and very little wood from the scion. The purpose is to expose a little cambium on the back side.
Another fine point to maximize chances of a bark graft taking (at lest with persimmons) is to be very accurate with the width of the bark peal so the scion fits exactly into the slot. Then I use my grafting knife and lightly remove bark only from both left and right sides of the scion exposing cambium.
When you do both of these things and use electrical tape to provide some pressure, here is what happens. First, when you peal the bark, there are cambium cells on both sides, the wood side as well as the pealed bark side. When you slide in the scion, the cambium exposed on each side also contacts the cambium of the tree on each side contacts the cambium you have exposed on the sides of the scion. When you bring the bark flap against the back of the scion, you get more cambium contact on that back cut. Finally, when you compress it all with the electrical tape, all the cambium contact is tightened.
One final thought. One other thing that can cause a bark graft to fail is water running into the graft. If you use more liquid (like Doc Farwell's) rather than pasty compound, it can also get into the graft so be careful when applying it. When I cut down my tree, I do so at a slight angle, not square to the ground. This causes any water to run off of the wound in a known direction rather than pool. I then choose grafting sites where excess water will not run because of the slope.
Thanks,
Jack
