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Flush Cuts & Bridge Grafts

Posted by Mason Colby 
Flush Cuts & Bridge Grafts
March 25, 2022 10:18AM
When cutting large or medium sized branches from a trunk would it make any sense to make a flush cut paired with bridge grafts?
Re: Flush Cuts & Bridge Grafts
March 25, 2022 02:33PM
Following years of not getting all our pruning done on certain blocks of young trees in our orchard (in a climate and on a rootstock that contribute to high vigor), we make a lot more large cuts this time of year than we'd like. The type of cut you make depends on placement and what you're looking for the tree to do in the future. If you make a truly flush cut, you'll be eliminating bud tissue, so don't look for any limbs to re-emerge in the future. Sometimes, as when you're cutting off a double leader (say you let another leader grow up as a potential replacement for your tree very low on the trunk, then don't need it), you may want to ensure just that. But most of the large cuts we make are not flush to to the trunk, but leave about 1/4 inch of tissue intact. This is about right for reducing water sprout emergence (leave a 1/2 inch, and the tree will be putting out all sorts of replacement sprouts), but leaving you options for the future.

As far as a bridge graft, it's interesting that you bring this up since a recent topic of discussion among some of us has been the notion that "trees don't heal, they seal." And it's usually a long process to seal over a large cut completely. I wouldn't consider it necessary to hurry the process via bridge grafting in most cases, unless they are some particular aesthetic reasons or it's an old tree lacking in health and vigor. One way to hurry the sealing process is to continually cut into the tissue, thus spurring the tree to keep patching on new growth surrounding the area in question (I think of it as re-opening a wound and the scar tissue that develops in a human wound). But it would have to be a pretty special situation for me to even go that route, and you'd want to think about the timing (wouldn't be making cuts like that during prime fireblight season, for sure).

You were specific in your ask about how to deal with large cuts, but I'll add one word of caution here, too: be wary of disrupting any natural sealing process. One of our huge old trees from the 1950s was subjected to rape by goat herd a few years back. My goats got out and started stripping the bark on the trunk. I didn't have time to deal with anything (a bridge graft in this case might have been very appropriate; the trunk wasn't girdled or anything, but getting there, effectively), but had some green wood sealer I was using to cap off apple wood logs to dry consisently for wood turning. The sealer was a natural blend with beeswax, and I thought I'd slap some of that over the wounds for temporary protection, like a band-aid. The tree's still with us, but that sealer application still sort of is, too, and those areas have never sealed naturally.

Kordick Family Farm
Westfield, NC
Zone 7a
Re: Flush Cuts & Bridge Grafts
March 25, 2022 03:27PM
Brittany's comment on the healing process is dead on. It is especially important that that "lower" portion (the proximal end) of the cut is left proud. This is hard to give a size recommendation on- it is proportional to the branch that is removed. Specific to the bridge graft idea, there are a few things to consider. It is certain, that anything that adds activity to the site tends to increase the vigor or extent of healing. This is evident in comparative studies of pruned branches and those with scions inserted. The latter always heal the cavity over sooner. There was an old nurseryman/orchardist I knew who encouraged healing by continually scoring the callus on the repairing wound. What will happen however, as with all bridge grafts that have multiple pieces is cavity formation. That is, you may get crap, moisture, etc. trapped behind and between the bridging shoots. That does not mean it won't work, but you need to keep an eye on things. Since this is a unique idea for this forum Mason, why don't you try the bridge graft of the same size as another wound or two to use as controls. Take some snapshots periodically and get back to us. This is exactly how citizen science works.

Walden Heights Nursery & Orchard
Zone 3 in Vermont
Re: Flush Cuts & Bridge Grafts
March 25, 2022 04:52PM
I am not sure exactly what the original reference was, but there is a form of graft (called a "strap graft"?) in which the scion is developed with a long tail of cambium wood on one side, (and a wedge of wood on the other side). The wedge goes under the bark on one side of a sawn-off small limb, (or, I suppose rootstock), while the long strap lies over the end of the stock, and is bent down into a slot cut into the bark on the other side. The concept is that the end of the branch is thus covered over with bark, (from the long strap bent over the end). But I think this very complex process is appropriate only in very specific circumstances, with particular plants. Apples are forgiving of the most vicious assaults, and I think something like this is vast over-kill.

Broomholm Orchard
Zone 5b in Nova Scotia
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