Monday, April 30, 2012

Bark grafts uncovered

    When I was out grafting trees last weekend, I also took the time to unwrap several bark grafts that I made last year. Its always interesting to see what's under the foil and how well the graft has calloused over (photo at right). A graft that has made strong top growth usually means you'll find a well knitted graft union.
      Here's a photo (at left) of a graft that didn't callous as well as the one pictured above. Even though the graft was successful,  the stock tree didn't provide enough energy to force the rapid expansion of the scion. Without fast scion growth,  the quick covering over of the wound made by grafting is impossible.  Grafts made late in the grafting season tend to to grow slower (like the one in the photo) than grafts made as soon as the bark slips in the spring.
     In contrast, a fast growing scion can nearly heal over a grafting wound in a single growing season (photo at right). Notice that callous tissue has formed all around the cut surface of the stock, leaving only a small circle of stump yet to cover. Here's a tree that will be producing nuts two years after grafting.
     When uncovering a graft, I often find a colony of ants tending their eggs in the warm, moist environment provided by that aluminum foil and plastic bag (photo at left). Ants usually don't interfere with callous formation, but they can enhance the decay of the stock stump. Once exposed to the sun, the ants will disappear.
   A technique for limiting ant nesting is to remove all wraps in August (in the year of grafting) and painting the graft union white. White latex house paint will protect the graft union from sun scald while eliminating the protected environment ants need for nesting.
     As always, make sure to support all bark grafts with a sturdy stake until the grafting wound is completely covered by new wood growth.