Tuesday, January 29, 2013

Dormant pruning pecan trees

    Many folks that have grown grafted pecan trees become frustrated by the seemingly unruly growth habits of their trees (photo at right). That's why I have developed some simple rules for training young trees that can help you get your trees off to a good start. Sometimes, however, pecan trees seem to just get ahead of your best pruning efforts. That's when I receive photos of trees in my Email accompanied with cries for pruning advice.
   With the spring like weather we had yesterday, I decided to prune a couple of trees and photograph the cuts I made. The first thing you will notice about pruning pecan trees is that every cultivar seems to have it own growth form. So I photo-graphed the pruning of a Jayhawk tree (spreading growth habit) and a Faith tree (upright growth habit).

     Lets start with the Jayhawk tree (photo at left). The first thing you will notice should be that my efforts at directive summer pruning has created a fairly well balanced Jayhawk tree that doesn't require a lot of corrective pruning during the dormant season. However, I have two objectives for pruning at this time of year: Remove a lower limb and remove any branches that are obviously heading in the wrong direction. To illustrate my pruning cuts, I've created side-by-side photos that represent "before" (left side photo) and "after" (right side) shots of the same pruning cuts. Hopefully, these photos will help demystify the art of pecan tree pruning.
     Here's the lower portion of the Jayhawk tree (photo at right). The red arrow points to the lower limb I plan on cutting out. I used a  pruning saw to remove the limb, cutting just outside of the branch collar. In pruning out lower limbs, don't get in a hurry. Remove only one or two lower limbs per year. Take too many lower limbs off at one time and you will end up with a sunburned trunk and massive cambial death on the southwest side of the tree.

  Next, I looked over the side limbs for possible corrective cuts. In the photo at left, the red arrow is pointing to a portion of a side branch that is pointing straight upward. This upward-growing shoot is directly competing with side limbs trying to grow outwards just above. To encourage the outward growth of the side limbs, I made a "bench cut" by removing the upward growing portion of the limb, cutting back to a outward growing side shoot.

    As a tree grows larger, it becomes more difficult to see where you need to make summer pruning cuts. Near the top of the Jayhawk tree, I discovered a side limb trying to outgrow the central leader. This happens frequently when a side limb points due south (towards the sun) just like the limb in the photo (above, right). I should have pruned this limb last summer to direct its growth outward but didn't notice the problem until this winter. I used a pole pruner to make another bench cut. The red arrow points to the limb that needs pruning while the red circle highlights the resulting bench cut.

    My final cut on the Jayhawk tree was to preserve the central leader. At the top of the tree I had two shoots growing straight up. Using the pole pruner I removed one of  the shoots (red arrow, photo at left). There will come a time when my Jayhawk tree grows too tall for pruning the central leader. Once the tree is out of my reach with a 16 foot pole pruner, I'm done trying to maintain a single central leader. Twenty feet of single trunk is good enough!

    Now let's look at the before and after photos of the Jayhawk tree (photo a right). This tree was fairly well balanced before I started and didn't need a lot of pruning. Look carefully and you should note that the central leader is better defined in the "after" photo. That is exactly what I was after when I picked up my pruning tools.

    The next tree I pruned was a Faith tree (photo at left). In the photo, note that the side limbs want to grow upwards instead of outwards. In approaching this tree, I had the same two pruning objectives as before: Start removing lower limbs and remove any branches that are obviously heading in the wrong direction. There is one more thing I like to keep in mind while pruning during the dormant season. I try to take off as little wood as possible because dormant pruning can force vigorous regrowth often in awkward and unexpected directions. This wild regrowth can become an even greater pruning headache.
    I started at looking over the lower limbs (photo at right). The first thing I noticed was that one of the lower limbs was growing strongly upwards (red arrow). Rather than taking the entire limb off all the way back the the trunk, I made a bench cut to outward growing side shoots.

   After making the bench cut, I still needed to remove a lower limb. On the left side of the tree I noticed that I had a limb directly above one of my lowest limbs. I removed the low limb (red arrow) knowing that the upper limb (green arrow) will fill out that side of the tree.

    The upward growing tendency of this Faith pecan tree meant that I spent a lot more time on this tree making bench cuts. In the photo at right, I removed a strongly upward growing shoot (red arrow) by cutting back to some outward growing side shoots. I made many more bench cuts within the canopy of this tree to encourage the growth of the central leader.

    As you can see from the before and after photos (at left), the Faith tree had much more wood removed than did the Jayhawk tree. The removal of just one lower limb and a bench cut on the other low limb opened up the tree considerably. Although not perfect, I hope you can see that the central leader is better defined after pruning that it was before.    
    Don't expect to correct all your trees problems during a single pruning session. The tree will continue to grow and you will need to keep removing lower limbs and pruning limbs growing in wrong directions. Pruning pecan trees is a process that requires patience and a good eye for tree structure. Developing the well-balanced, strong trunk of a mature pecan tree will take years.