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I used to think a flush cut was the only way to prune a branch collar
Last spring, I was working on a mature oak in Springfield and made a clean, flush cut against the trunk. The client, an older gardener, pointed out the small circle of discolored bark forming around my cut a month later. She said, 'That's not healing, it's sealing you out.' I looked it up and learned about the branch defense zone trees form. Now I leave that slight collar, about a quarter inch out. Has anyone else had to unlearn a 'clean cut' habit the hard way?
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emerychen2mo ago
My arborist exam in 2012 had a whole section on compartmentalization. The book answer was always to cut just outside the collar. But on actual job sites, especially with fruit trees or maples, I've seen that quarter-inch stub become a perfect entry point for borers or rot. For a lot of species, a truly flush cut that doesn't gouge the trunk actually allows the callus to roll over smoother in my experience. It depends entirely on the tree and the size of the branch.
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ray_mitchell582mo ago
Look, I get what @emerychen is saying about stubs, but is a quarter inch really going to doom the tree? Most of the time that little bit just dries up and falls off. I've seen way more damage from people hacking into the trunk trying to get it perfectly flush.
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That older gardener in Springfield was right about the bark discoloration. Emery, when you say a flush cut lets the callus roll over smoother, are you talking about a specific type of maple? I've seen sugar maples get really gummy around a flush cut and it seems to stall. Does that gumming interfere with the compartmentalization you mentioned?
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