Monday, April 18, 2011

Pecan tree growth patterns

    Pruning pecan trees can be frustrating. Every spring when you go out to look at your young trees you find 2 to 3 limbs growing every which way but straight up. So you hack away at the tree hoping to create a tree with a strong central leader. The young tree pictured at left is typical--4 limbs all growing from the same general area. Two of the limbs look like they want to be the dominate central leader.
    To prune this tree, I would cut out one of the two upright growing limbs. Leave the limb on the southern side if possible. The second limb I'd remove is the right-hand branch because of its narrow crotch angle. I'd leave the obviously, less-vigorous left-hand branch alone.
    Pruning is made a lot easier if you come to understand why pecan trees grow the way they do. As your trees start to leaf out this spring, take a close look at the terminal growth (photo at right). Believe it or not, pecan has strong apical dominance. Notice how the very top of the tree has already developed new shoots while the buds further down the stem are just starting to pop. As the top of the tree grows, the leaves manufacture a plant hormone that sends a chemical message down the stem to suppress the growth of lower buds.
     Now take a closer look at the emerging new growth (photo at right). I count 4 new shoots all coming from the top 2 inches of last-year's wood.  Leave this cluster of new shoots to grow for the entire growing season and you will end up with the same pruning chore pictured at the beginning of this post, but only two feet higher in the tree.
     You can save a lot of pruning time by addressing this growth pattern early in the growing season. Once the new shoots have grown out about 6 inches, I prune the top to a single new shoot. The easiest way to do that is to locate the lowest shoot in the cluster of shoots and then cut off the stem just above that new shoot (see related post). This removes all the competing shoots above that point and you should be left with one 6 inch shoot that will grow to become your central leader.