Thursday, May 11, 2017

Training last year's bark graft

    When grafting a vigorously growing tree with a bark graft I often produce a tree with 5 to 7 feet of new growth on the scion during the first summer. I achieve that kind of growth by meticulously  pruning to preserve a strong central leader. But by the end of the growing season, I usually find that I've created nothing but a tall, branchless tree. When the one-year-old graft breaks bud the next spring it seems like all the new growth is confined to the very top of the tree (photo above, right). How am I going to promote lateral branch formation with a tree like this?  All it takes is some careful directive pruning.

   In pruning this tree I start at the very top then work my way down.The photo at left shows the cluster of new shoots that have developed at the very top of the tree. If I were to leave all these shoots in place, I would quicky lose my central leader and the tree would be topped by a sprawling assembly of branches pointing in every direction but straight up. In addition, allowing the tree to grow freely at the very top of the tree will create a top-heavy tree that causes the tree to bend over under the weight of the foliage.

     My first pruning cuts were made to encourage the growth of a single new leader. Here's where I use the 2-foot rule in tree training. In the photo at right, you can see that I removed all the the new shoots in the area of the trunk two feet down from the apex of the shoot that I have choosen to become the new central leader.

   When pruning off all the lateral shoots that are directly competing with the new central leader, I was careful to leave all secondary buds in place (photo at left). A few of the secondary buds had started to push and that's OK. The just-emerging shoots from secondary buds won't be able to catch up with the strongly growing central leader. In addition, shoots that develop from secondary buds form lateral branches with wide crotch angles (a good thing). 

    After pruning the top of the tree using the two-foot rule, the top of my tree has a single central leader and has lost its bushing appearance (photo at right). My next pruning task was to work my way down the stem and thin out the dense array of lateral branches that I found growing there (photo at right). There is no way the tree could support that many lateral branches all within about 18 inches of trunk.

    I removed more than one-half of the lateral branches that had formed on this portion of the trunk. In pruning lateral branches, I was careful space out the remaining branches both up and down  and around the trunk (photo at left).  After pruning, the entire tree no longer appeared so top heavy with foliage
    Thinning out lateral branches near the top of the tree has an additional advantage. Buds lower down on the trunk will be stimulated to grow and form branches along the entire length of the last year's scion growth.

    Stepping back from the tree that I just pruned, I could see that the new shoots and foliage were now better distributed along the main trunk (photo at right). The ladder in the photo is 4 feet tall to give you a better idea of the size of the tree I was pruning. With lots of lateral shoots developing already this year, my single shoot graft should turn in a well bushed out tree by the end of its second growing season. Maybe by year three, I'll be producing a few nuts on this tree.