Tuesday, January 8, 2013

Pruning a neglected pecan tree

    A lot of pecan growers have read this blog and learned pruning basics. Along the way, I've introduced you to some important concepts for tree training including the 2 foot rule and directive pruning. These methods are designed to be used on young trees and if followed diligently will result in a well balanced, central-leader pecan tree.
    However, all too often, young pecan trees don't receive the necessary intensive training and end up with multiple leaders and numerous narrow angled branch connections. Grafted trees are especially prone to developing poor tree structure because of the tree's natural tendency to produce multiple growing points on terminals. Recently,  a grower in Georgia set me this photo (at right) of a 'Sumner' tree that he inherited when buying a pecan orchard.  His question was simple--"How should I prune this tree to a central leader?".  The simple answer is--"Not all at once". Since trees are three dimensional objects, it is a little difficult to illustrate how this tree should be pruned using two dimensional photographs. However, I'll try my best and hopefully, I'll convey some general pruning guidelines.

    The first step in pruning this tree is to decide which limb should become the central leader. This tree has 4 major limbs all trying to compete for the role of central leader. In the photo at left, the yellow arrow points to the limb I would leave unpruned and the limb I will encourage to become more dominate by pruning the other 3 major limbs. There is one thing to notice about the limb I have chosen to become the central leader. Above the arrow, all the side shoots that radiate off this limb have fairly good branch angles. That bodes well for the future strength of this tree.
    This tree is just starting into its nut production years so I don't want to cut more than one third of the canopy out of the tree in a single year. I'll start by making a heading back cut on each of the other major limbs. This allows the central leader full access to sunshine and will stimulate it to become more dominate. On the other hand, heading back cuts will slow the growth of the other major limbs and force them into more secondary positions. The first heading back cut is shown at right. I'd cut the upward growing portion of the limb back to the point of an outward growing branch. The cut line is marked by a red slash in the photo at right.
    Moving to the other side of the tree, my second cut is shown at left.  Note that I've chosen to prune this limb at the point were it starts to turn upward and strongly compete with the central leader. Again the cut is made to an outward growing shoot and is marked by a red slash.
   My third and final cut is a little difficult to see because its on the back side of the tree.  However, this heading back cut is made just like the other two. The limb is pruned to an outward growing side shoot, removing the portion of the limb that was in direct competition with the central leader (photo at right).  All three heading back cuts are shown by red slashes in this photo. That's plenty of wood to remove in a single year. Ultimately, pruning this tree so it will develop a single strong trunk will be a multi-year project.
     You will find that the limbs that you head back will develop epicormic sprouts near the pruning cut. These sprouts will grow straight upwards trying to take advantage of suddenly available sunlight. You'll need to prune off these sprouts until such time as the central leader grows large enough to start shading them out (1-3 years depending on tree growth rate). Once the central leader starts to dominate, I'd remove the lowest  major limb entirely all the way back to the trunk (photo at left). Over the next, 3-8 years, I'd work my way up the trunk removing the other two narrow-angled branches at 2-3 year intervals.
   Here are three basic principles to remember in pruning young, nut-bearing pecan trees.
  1. never prune more than 1/3 of the canopy out of a tree.
  2. use heading back cuts to slow the growth of side limbs and direct their growth outwards.
  3. remove lower limbs over time. Cut only one major limb every 2-3 years. Your goal should be to develop a tree with 8 to 10 feet of clear trunk.