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Emergency Grafting: An Introduction September 5, 2013

Filed under: Gardening,Grafting — acgheen @ 12:00 am

“It’s an eight foot branch!” Panic filled my mother’s voice.  I could empathize with her devastation.

The maple had been in the yard for nearly a decade and, as if in defiance of the natural laws of the community, had grown to a healthy, sprawling, twenty feet – enough to shade the bedroom window and cast an enveloping shadow across the yard.  Unfortunately, the Fall day’s heavy snows had threatened to change all of that.  Despite regular trips into the yard to knock the deposits from the branches, the weight had grown too much for the mature limbs to bear and one of the chief branches had snapped, tearing a sizeable gash through to the heartwood.

“Don’t panic yet,” I replied.  “I may be able to save it with a bridge graft.  I’m on my way home right now.”

Due to the near blizzard conditions, the drive home was a slow one and, as I gazed through the thick curtain of white, I was forced to wonder just what I had gotten myself into.  While a bridge graft could (in theory) save the top third of the tree, I was acquainted with the practice only in theory.  I had never actually performed the procedure and this seemed a rather dramatic way to begin.

Upon arriving at home, I grabbed my pruners and grafting knife, quickly reviewed the process as aptly illustrated in both my Master Gardener’s Handbook and a local nursery flier, and headed into the yard.  A quick look at the wound was sufficient to let me know that the tree probably wouldn’t recover if something was not done quickly.  The collapsing eight foot limb had torn through an inch of healthy cambium tissue, leaving a wound that was a good eight inches long and another four inches wide.  Despite the frigid conditions and the snow that was soaking my clothes, I set to work.

My initial job was to trim away the bits of bark which had once covered the healthy tissue of the missing limb and dry the wounded area.  With the heavy, wet snow falling like a late summer downpour, this was a challenge.  It was important, however, to remove the moisture from the injured tissue in order to prevent rot or the introduction of infectious disease to the limb.  After soaking through several hand towels, I finally managed to get the area dry enough to begin my surgery. I proceeded with the towel clamped firmly in place by one of my over-sized gloved hands. (Because the process of bridge grafting involves making fresh cuts just outside the perimeter of the wound, were I to do this again, I would take a moment to coat the dried tissue in a layer of pruning paint or wax to keep the tree’s natural moisture in and additional moisture out.)

The downed branch had not yet outlived its usefulness and I carefully selected an handful of fresh, supple, pencil-width branches which would serve as scions.  Trimming them several inches longer than the gap which they would bridge (two to four inches is standard depending upon the size of the wound), I then made an angular slice in both ends of each twig.

It is important that these cuts expose a sizeable portion of the scion’s cambium layer (the white tissue which lies beneath the bark), generally an inch or more.  This is the layer through which sap flows and it must be in firm contact with the tree’s cambium layer in order for the graft to take, so take care to ensure that the cut is smooth and level.  It is also important that the cuts be made on the same side of the scion if they are to bridge the wound.  You will know if you have done the process correctly if you can bend the scion into a bridge shape with both of the cuts forming the “base”.  It is important that these cuts not be allowed to dry out before or during the grafting process.  In warm, dry weather, the scions may be temporarily wrapped in a damp paper towel.

According to the directions I had read, the next step was to make fresh cuts in the trunk just beyond the top and bottom edges of the wound, allowing the scion to restore the flow of sap to the top of the tree.  These cuts need to be deep enough to separate the bark from the tree’s cambium layer, but no deeper.  (A deeper cut will not harm the tree or reduce the chances that the graft will take, but it does require extra labor to make such a cut and, with no advantage to doing so, it is not advised.)  The bark, itself, should be left attached to the tree, since it will help to hold the scions in place.

The first scion was then inserted with the bridge’s “base” facing inward towards the tree and fastened in place at either end with a brad.  I chose to use a brad gun, though a staple gun might do just as well.  (Though some literature suggests hammering the brads in by hand, I found this to be a tedious process which was made even lengthier by the tendency of the scion to slip out of place with each blow.)

I repeated this process several times until the entire wound area had been bridged, then dried the wound once more and sealed the work with grafting paint.  (Grafting wax is a better choice, if you happen to have some on hand.  If not, the wax from a toilet ring makes an excellent substitute and is available quite cheaply at most hardware stores.)  I then wrapped the entire project in a light, cotton tree wrap, further securing the scions in place.

To my delight, spring finally arrived and, glancing out the window one morning, I noted that the maple was in full bud.  Throughout the season, the limbs saved by the graft continued to flourish, putting on new growth and looking (to my great delight) as though they had never suffered a moment of trauma in their lives.

Bridge grafting is a labor-intensive process, but may be easily performed by most backyard gardeners.  I recommend that you keep the tools for this simple “emergency surgery” (pruners, grafting knife, pruning paint or wax, and brads) on hand at all times.  It can be a genuine “life-saver” for a tree which has been damaged by weather or wildlife, preserving the beauty of your yard for years to come!

(The University of Minnesota has a wonderful webpage on budding and grafting.  You’ll find detailed instructions on performing a bridge graft, along with illustrations at the bottom of the page!   http://www.extension.umn.edu/distribution/horticulture/components/dg0532c.html)


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