Tuesday, April 5, 2011

Bark graft maintenance

    Early spring is a good time to look over last year's bark grafts. In the photo at right, you can see that two grafts were applied to this tree last year but only one of the two took off and grew. We left the aluminum foil and plastic bag (applied at the time of grafting) on the tree to protect the graft union over the summer. You can also see a strong wooden stake attached to the tree used to support the graft and prevent wind breakage.
     First step is to remove all wrappings. When I removed the foil, the failed scion just fell off the tree (there was no callous formation to hold it in place). You can clearly see callous tissue formed at the top of the stock where the scion was inserted under the bark (photo at left).
    My second step in maintaining this graft is to trim the top of the stock. If you look carefully, you'll see a distinctive swelling in the stock's bark that runs at a diagonal from scion to the opposite side of the tree--about 1.5 inches down the trunk. To enhance the healing process, I'll  cut the corner off the stock just above that swelling.
    To find the exact angle and location to trim the stock, take your knife and peel back some of the bark on the side of the tree opposite the graft. You'll find that the tree has formed a natural barrier to wall off the wound you created in grafting. Above the barrier the bark will be dark and even decaying. Below the barrier the bark is alive and tan in color. In the photo at right, I'm using a hand saw to cut away the dead wood above the barrier. Note the tan, living bark below the cut. Also note that I'm cutting just above the diagonal swelling in the bark.
     By trimming the stock at the precise location the tree is trying to seal off the wound, you will enhance the healing process and reduce the time needed to keep the graft supported with a wooden stake.
  The final step in early spring maintenance is to prune the tree. Remove some of the lower limbs to force more of the tree's energy into the scion (note the fresh pruning wound below the graft union). Next, prune the scion so you'll have a nice central leader tree.