I followed Walter Zill method top work my sister Home Depot mango tree 2 weeks ago. Yesterday I checked and had around 6 grafts and 100% took!!! I didn’t have store bought parafilm and just used strips cut from plastic bag. I covered the whole scion as he did, and then uncovered the top grow after 2 weeks. Not as hard as I had thought, even at end of October.
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sapote, next time please show/explain how you cut the rootstock. Walter Zill did not do a regular straight cut because the inside wood is untouched and just popped out and therefore leaving the cambium also untouched. This explains why this kind of graft works. The trick is in the cutting.
Yes, the secret is the cut depth. I made first cut not deep to cambium, which gave me more insight for controlling the depth of next cut. Sink the knife at the top of the cut until hit the wood then back up about 1mm for 1st cut. For 2nd cut, sink the knife until touches the wood, then tilt the sharp edge up to pry the thin bark so the thin bark slips (or pop) off the cambium, and this is the correct depth to pull the knife down to bottom of the long cut, no more no less. Done.
Along the length of the long cut if the knife got in to the wood a little bit, no worry because there is plenty of good cambium contact remain for the scion. Don’t have to be 100% cambium interface to survive. If some sections not deep to cambium then easily just “touch up” again to slip the thin bark off to expose cambium.