Tuesday, May 5, 2015

Making an arrowhead bark graft

   During last week's grafting schools, I received a lot of questions about the arrowhead grafting technique. The arrowhead is my "go to" method for inserting a small diameter scion (3/8 inch)  into the stock tree that is roughly 0.75 to 1.25 inches in diameter.  The photo at right compares the size of my scionwood to a small stock tree that needs grafting.

    I cut off the stock tree at a point just below a bud. This will give me a nice, long area of clear stem in which to insert the scion.  The photo at right gives a clear comparison of the diameters of scion and stock.

    To prepare the stock, I make an incision through the bark, straight down the stem about 3 inches long (photo at right). It is always best to make this cut longer than you need so you won't tear the bark when inserting the scion. 

  Now it is time to carve the scion. Start by making a sloping cut about 2.5 inches long at the base of the scion. Thin down the wood until you get a long tongue shape while carving a shoulder at the top of the cut (photo at left).

   Now, we get to the reason this method is called the arrowhead graft. Turn the scion so you can see the edge of the tongue. Using your knife, peel off the bark all along the edge of the scion from the base of the shoulder to the bottom of the scion stick. When I make this cut, its like I'm trying to sharpen an arrowhead.

    In shaving off the bark, make sure you cut deep enough to expose white wood all along the edge of the scion (photo at left). Only by seeing wood exposed will you be certain you have exposed cambium down the entire edge of the scion. 

    Next, turn the scion over and sharpen the other edge of the arrowhead. When you are done carving, you should see a long V shaped strip of bark down middle of the scion (photo at right).

    To make it easier to insert the scion under the bark of the stock, I cut a small chisel point at the tip of the arrowhead (photo at right).

    After creating my arrowhead scion, I lift the bark on the stock and slide the scion right down the center of the bark incision (photo at left). As I push the scion downwards, I wiggle the stick side-to-side to make sure the bark is lifted away on each side of the incision. 

     I push the scion down to the point where the shoulder of scion contacts the top of the stock. If the scion is positioned correctly, all you should see is the V shaped bark strip on the scion peeking out from the slit in the stock's bark (photo at right). 

     From the side, it looks like I have a nice tight fit between scion and stock (above), but look from above the graft and you'll see gaping holes between bark and scion (photo at left).
    To form the bark up tight around the scion, I use a light duty staple gun with 5/16 inch staples. The staples are inserted vertically right along each edge of the scion (photo at right). These staples force the bark to bend inward ensuring the the bark of the stock is contacting the cambium exposed on the edge of the arrowhead.

   Now let's check from above. Once the staples are inserted the bark is nice a tight and all the air gaps have been eliminated (photo at left).

   I use staples to force the stock's bark to conform to the scion. However, these staples to not hold the scion in place. Touch the scion the wrong way and the stick will pop out away from the stock. To secure the scion in place, I use grafting tape to wrap the entire graft union (photo above right).

    I finish up the arrowhead graft just like all the other grafting methods I use for pecans (photo at right). I cover the graft union in aluminum foil to block out the sun. I then cover the graft with a plastic bag and add a spot of school glue to the top of the scion to preserve moisture. And finally, I never forget to tape on a bird perch to prevent bird damage.