Monday, April 11, 2011

Anatomy of a Bark Graft

    Ever stop to think about how truly amazing the process of grafting is? A seedling tree accepts a scion then pushes it to grow a whole new tree crown. I've been grafting for over 30 years but I still stop to marvel when buds start to push on a newly placed scion.
    Recently, I cut down a tree that had been bark grafted five years ago. I wanted to learn a little about the anatomy of a successful graft. After cutting the graft union from the rest of the tree, I used a band saw to slice open the wood. The photo at left shows what the band saw revealed.
     You can immediately see the top of the original stock tree (marked A) that had been trimmed at an angle to promote healing. Also, note the top of the original scion buried under years of wood growth (marked B). This cross section of a graft clearly demonstrates that trees never really heal their wounds, they just grow new wood over the damaged tissue.
    In any orchard of grafted pecan trees, it is usually pretty easy to see a change in bark texture associated with the graft union. Genetic differences between rootstock and scion are also noticeable in the wood. You can see a clear line (marked C) across this tree's trunk that marks the change from rootstock to scion cultivar. Note the line runs nearly straight across the tree at a point where the top of the stock meets the bottom of the scion. The strong dip in the line (marked D) is actually part of the original scion that was slipped under the bark during the grafting process.