Friday, October 19, 2012

Common tree training mistakes

    A couple of weeks ago, I visited an orchard of young pecan trees growing in SE Missouri. The owner was obviously proud of his trees and was excited by smattering of nuts produced by the trees. However excited he was by the performance of his trees, I was even more thrilled to find a single location to photograph all the common mistakes growers make in training young trees.  
    I've talked at length about training young trees in previous posts. Almost all of the mistakes growers make in training young trees are related to a lack of appreciation for a pecan tree's natural growth patterns. Lets look at some examples.

     In training a young tree, developing a strong central trunk and wide angled lateral branches is critical for supporting a heavy crop of nuts. Here's a tree with no obvious central leader and several narrow angled branches (photo at right). The branch pattern seen in the photo developed a long time ago--all the way back to when this tree was a recently planted nursery tree. As growth began that very first spring, 3 to 5 buds near the terminal of the tree broke all at once and started growing. From the looks of the branch structure, even some secondary buds broke at the same time. This common bud break pattern is the reason summer pruning is so important for developing a central leader tree. Pruning the terminal of a young tree to a single growing shoot shortly after bud break is critical for defining and keeping a dominate central leader.

     Allowing a tree to develop two major leaders is another common mistake (photo at left). The narrow angled crotch between the two forks of the tree is inherently weak and subject to breakage. Sure, correcting this problem is easy--just use a chainsaw to remove one on the two leaders. However, waiting to correct this problem until this point in a tree's life will result in removing one half of the canopy and 1/2 of next year's nut crop.
    The photo at right is an example of what happens when a tree gets over-pruned. Growers are often in a hurry to 'push' a tree taller--it makes it easier to mow around. But pruning too much can cause the tree to grow in unexpected ways. In this case, the sudden exposure of the trunk to full sun has caused epicormic sprouting along the lower portion of the trunk.  If trunk sprouts had not developed on this tree, the southwest side of the trunk may have become scalded by the summer sun. Sun scald has the potential to kill the trunk's cambium on the exposed side of the tree and slow trunk diameter growth. 
     Lower limbs need to be removed slowly, over time. My rule of thumb is to never remove more than two lower limbs per year.
    For detailed instructions for training young trees including "directive pruning" and the "two foot rule" read through my blog series starting here.