Tuesday, May 17, 2011

Bark grafting

   When you live in an area were native pecan trees are plentiful, young trees seem to pop up everywhere. This is the case on my farm. I've been mowing around volunteer trees allowing them to grow to a point where I don't need to bend over to graft them (I can graft much faster standing up). I  let the seedling trees grow 5 to 10 feet tall (1.5 to 2 inches in diameter) before using a bark graft to establish my chosen cultivar. There are several variations in bark grafting but I've become comfortable making my version of the modified rind graft.
    All bark grafting methods are similar. The scion is inserted between between the bark and wood on one side of the stock. The key to successful bark grafting is to make certain that cambium on the scion is placed in direct contact with cambium of the stock.

    To start the modified rind graft, cut off at least 1/2 of the stock leaving a stump less that 4 inches in diameter (for faster healing I prefer trees in the 1.5 to 2.5 inch diameter range) (photo at left). 
     Next, inspect the stump and look for the "flat" side of the stem. On the flat side, make a downward incision with your knife cutting trough the bark around 3 inches long.(photo at left)
   Now it is time to carve the scion into a shape that will fit under the bark and maximize cambial contact. I start by making a deep cut, removing about 2/3rds the thickness of the scion, This cut is about 2.5 inches long and features a pronounced shoulder at the top of the cut.(photo above)

   I turn the scion over and make a shallow cut into the wood of the back side of the deep cut. This cut is not made parallel to the deep cut but angled to one side. When finished, I have a thin piece of bark adjacent to the deep cut on one side and a much thicker strip on the other. The cut on the back side of the scion should start just below the shoulder of the deep cut and should give the scion a wedge shape when completed. (photo above)

     Next I make a third cut perpendicular to the deep cut along the thick bark strip edge(photo left). I make this cut  just deep enough to expose the cambium and I make certain to leave a strip of bark between the backside cut and the perpendicular cut. At this point my scion has triangular shape in cross section.  I complete scion preparation by making a chisel point on the end of the bud stick (photo above). This final cut should be made on back side of the scion. 

   Now I'm ready to insert the scion into the stock. I use my grafting knife to gently pull the stock’s bark away from the wood on the left side of the bark slit. Inserting the scion between the bark and the wood of the stock, I tap the scion down into the stock until the shoulder of the deep cut fits snugly against the upper side of the stock.  The deep cut should be facing the wood, while the shallow cut should be covered by the raised bark flap and perpendicular cut should fit snugly against the bark slit. (photo at left)
    I secure the graft union with staples (use a 5/16 staple from a light duty staple gun such as Arrow model JT21). It is important  staple down the bark firmly against the scion and to be sure that all air pockets are removed. (Photo at left)
    Like all the grafting methods I use,  I cover the graft union with aluminum foil and a plastic bag. And finally,  I attach a bird perch stick to the stock with black electrical tape  to prevent the birds from breaking out the scion. (photo at left)
    See related posts on maintaining a bark graft one year after grafting and the anatomy of a successful bark graft.