Thursday, June 13, 2013

Answering pruning questions

   Training young pecan trees is one of the most popular series of posts on this blog.  Many pecan growers have used my directive pruning techniques and had excellent results. But, all your pruning questions have not been answered. Recently, I've received photos from a couple of pecan growers seeking additional pruning advice. Rather than just respond to each grower individually, I've decided to share those photos on this blog so everyone can benefit from additional pruning examples.
    I received a photo of a young pecan trees with the simple question--" How should I prune this tree?" (photo above, right).
    At some point in the past, the top of this tree had been pruned off leaving a 2 inch stump and no strong central leader. Currently, this tree needs more training than actual pruning. First, I'd start by cutting off the stump at the top (cut marked in blue). Next, I'd drive a wooden or steel post next to this tree. With the stake in place, I would tie the uppermost branch to the stake, holding it in an upright position and forcing it to become my central leader (the future tree trunk).
    If you look carefully at this upper branch, you will note that side shoots are starting to develop (see area in the red oval above). Here's where you practice the 2-foot rule by removing all side shoots along the upper 2 feet of the central leader.
   The final step in training this tree is to slow the growth of the lower side shoots. I simply pinch out the growing point from each shoot using my fingers.  This should push more of the tree's growth energy into the central leader yet maintain a healthy level of foliage on the tree.
   The next pruning question concerned choosing a central leader. Proving that I'm not the only one that can use a computer to label things in a photo, this grower asked- "I believe the central leader should be 'A' but the other shoots marked 'B' and 'C' are out growing the assumed central leader. Should 'B' and 'C'  eliminated or pruned back?" (photo above).
    The quick answer is: 'B' and 'C' are leaves and not competing shoots. Don't prune them. The reason they are taller than the terminal of the central leader is because these leaves are older than the leaves at the terminal and thus more fully expanded. (By the way, I love the deer cage).
    This confusion between what is a leaf and what is a shoot gives me the opportunity to give a breif lesson in pecan botany. Pecan trees create what are known as pinnately compound leaves (photo at right). Each leaf is made up of 9 to 17 leaflets attached to a stem-like rachis. The base of the rachis is also known as the leaf's petiole. An axillary bud is found just above the connection of petiole and stem. Each fall, the tree sheds entire leaves including all leaflets and rachii.  The only thing left behind will be axillary buds and a heart shaped leaf scar below each bud.
    In training a young tree, you should keep your eyes on the axillary buds developing on the central leader. By early summer, stalked buds often form on a vigorously growing central leader.  The photo at right was taken this morning and a stalked bud has already formed (inside yellow oval). Allowing a stalked bud to develop into a branch creates all kinds of tree structural problems. Pinch off these stalked buds as soon as you see them. Not only will you prevent future tree branch angle problems but you will further stimulate the growth of the central leader.