Wednesday, May 4, 2011

Arrowhead grafting

     When I go out into the field to graft pecan trees, I bring my tools, supplies, fresh scion wood, and the knowledge of several grafting techniques. The method I use to graft a tree depends on both the size of the tree and the diameter of my scion wood. It an earlier post I talked about grafting pecan trees when the tree is ready . One of the trees on my farm had grown over 2 feet last year, so it was time for this tree to be grafted.

    The tree was about 1 inch in diameter so I  decide to use the arrowhead graft. The key to a successful arrowhead graft is in carving the scion into the correct shape. First whittle the scion down into a thin strap (photo left). This strap should be thinner and narrower towards the bottom of the scion. You should also have a pronounced shoulder at the top of the cut surface.
     Next turn the scion over and carefully shave some of the bark off of each side of the scion. Make sure to cut deep enough to expose a thin strip of white wood alone each edge (photo at left). By exposing the wood, you are ensuring that cambial tissue is revealed. A thin strip of bark should remain down the center of the scion. This graft gets it name from the two cuts you make on the back side of the scion. I looks like you are sharpening the edges of an arrowhead.
   It now time to insert the scion into the stock (photo at left). Cut at least 2/3 of the top off of the stock tree. Make a single vertical incision through the bark of the stock about 3 inches long. Insert the scion under the bark right down the center of the incision. You should see the strip of bark that you left on the back of the scion exposed through the crack in the stock's bark.  Note at this point the bark of the stock is cupped away from the cut surfaces (more importantly, the cambium) of the scion.
   To form the stock's bark closely over the scion, I use a light duty staple gun (Arrow JT21) and 5/16 inch staples. Starting at the bottom, I use the staple gun to press the bark up against the edge of the scion and shoot in a staple. I usually use 6 staples, 3 on a side, inserted vertically to hold the bark firmly against the scion (photo at left). It is a little difficult to see the staples because they are the same color as the bark, but you can plainly see that they have bent the bark inward.
    The success of this grafting method is dependent on how well you can force the stock's bark to conform to the scion.
   To secure the scion even further, I wrap the graft union with grafting tape (1/2 inch wide, 4 mill thick, plastic plant tie ribbon). The tape also helps to hold the stock's bark firmly against the scion (photo at left).
    I complete the grafting process by using the same wraps I use for all pecan grafting methods (photo at left). I prevent sun scald by covering the graft union with aluminum foil. To maintain high humidity around the graft union, I place a plastic sandwich bag over the scion and the stock (you'll need to rip a corner out of the bag). I use grafting tape to seal the plastic bag tightly around the scion then again around the stock just below the graft union.
    Last but not least, I attach a training stick/bird perch to the stock using plastic electrical tape (black tape). This training stick extends about 2 feet above the scion and creates a place for birds to land instead of on top of the scion. Many new grafts have been broken by perching birds when scions are not properly protected.
    Once growth starts on the scion, tie the new growth to the training stick with grafting tape to prevent the wind from breaking out your scion.