Thursday, May 12, 2016

Coppicing before re-grafting a large pecan tree

    Last year, I placed 9 bark grafts in a large tree in an effort to change a seedling tree into tree that would produce large, high-quality nuts (photo at right). Today, I spent nearly 90 minutes up in a hydraulic lift moving from graft to graft, trimming each graft union, and removing new sprouts growing on the trunk and main scaffold limbs. I can't imagine how long this task would take if I had to use a step ladder to access these graft unions.
    The hazards associated with grafting, pruning, and training a top-worked tree from the top steps of a ladder are obvious. No tree is worth broken bones and a extended recovery period. If you would like to graft a seedling tree that has grown too large for conventional grafting methods or you end up changing your mind on a previously grafted tree, consider coppicing the tree at ground level.    
   The practice of coppicing works pretty well for trees that have not grown over 10 inches in trunk diameter. Out in our pecan breeding plot, I've been removing trees that produce poor quality or scab susceptible pecans. As a result I have produced dozens of coppiced trees. The photo at left shows the current size of many trees in the breeding plot compared to a tree that was cut at ground level  a couple of years ago.

     In the two years since cutting the tree at ground level the tree has sprouted multiple stems from the stump (photo at right). The tallest sprouts have already grown to over seven feet in height. These fast growing shoots make excellent sites for bark grafting, and I can even make the graft with two feet firmly on the ground.

    Take a close look at the sprouts growing from the coppiced tree (photo at left). The sprouts are all growing from around the outside edge of the stump. These sprouts actually arise from epicormic buds buried under the bark of the stump.
    Before grafting this tree, I trimmed off all but the most vigorous sprout. Using my chain saw I cut off all competing sprouts at the same height as the stump (photo at right). The white wood in the photo reveals the location of the removed sprouts. The dark (stained) wood is the original tree stump.

    Once all competing sprouts are removed I have what looks to be the perfect tree for bark grafting (photo at left).  But be forewarned. The stump will produce additional sprouts this coming summer and I'll need to add stump-sprout removal to my list of summer pruning tasks.

     I usually recommend leaving a couple of lower limbs below a bark graft. However, this sprout had grown so rapidly that the lowest limbs were all above my preferred graft height. I figured that this tree had already survived coppicing, so a brutal cut for placing a bark graft couldn't hurt. I placed the graft at a comfortable height for both grafting and for summer training of the sprouted scion. Judging from the vigor of the stump sprout, this scion should make at least 4 to 5 feet of new growth this summer. I'll need to watch this tree carefully. Summer pruning to ensure a central leader and careful tying to a strong stake will be critical for graft success.