Managing Light in the Orchard, The First Step

This is really a talk about pruning of apple trees. No subject draws more cultural comment or creates more uncertainty as to just what is right and what is inappropriate.

As we increase the density and investment risk of our orchards in Ontario there is less room for bad decisions when pruning. These decisions can be related to when pruning is carried out, who is qualified to do it, how much can we afford to spend on it, and what should the resulting product look like. We cannot afford to forget other cultural practices and how they relate to pruning. Trees where heavy pruning is done this winter will require much less nitrogen than usual.

My take on winter so far is that it's been relatively friendly in terms of minimum temperatures and number of good working days with the clippers in hand. Cold has been steady but not severe as far as apple culture goes.

The more southerly production areas can normally spread the risk of timing over the entire winter. Many will start with more mature trees and trees with less value before Christmas. Normally, the results are okay. The problem lies with the volume of work to be done. Typically, the pruning job can last for months unless there is a small army of pruners involved.

At this latitude, the desired tree shape is a narrow pyramid or cone. In other words, narrow at the top and gently flaring at the bottom. This basic shape will vary somewhat with density. As we know, light is the fuel that drives the whole fruit production process in the orchard, however, it's only free to the top of the tree. How it gets distributed throughout the canopy will largely determine the value of the crop.

I am always amazed at how quickly a tree can loose its ability to produce quality fruit in the most economically desirable part of the tree canopy. The objective of every pruning program should be to create an even distribution and density of quality fruit buds within the managed canopy. This is only possible when light is able to reach all zones of the canopy on a more or less structured and uniform basis.

One of the keys to doing an effective pruning job is to be able to visualize what a tree would look like if left alone. Trees left unpruned for a year quickly loose their ability to efficiently colour the bulk of the crop. When pruning is not done for two or three successive seasons, yields drop dramatically as quality fruit buds become hard to find.

Many times, a tree can look entirely different when one or two large and intrusive limbs are taken from the upper canopy. These limbs when left look like trees growing within the tree canopy. The temptation can be to leave them because they sometimes have great looking fruit buds. Granted, you do gain quality yield in that area of the canopy but sacrifice too much to get it. These branches will effectively prevent you from producing any sort of quality in two or three times the volume of space under that branch. Train yourself to recognize those branches "trees" growing in the tree canopy and eliminate them with a dormant cut.

Publication 814 " Pruning and Training of Apple Trees" has been revised for Ontario. It includes detailed information on all of the popular and world class training systems that we are now familiar with. Included also is an appendix describing some of the traits of a number of cultivars including many of the new and highly talked about ones. On the next page is a photo (Figure 1) of a mature spindle on a size controlling root system. The upper middle canopy of this tree is requiring attention. Tree-like growth in the top of the tree will shade out a large % of canopy in the middle and lower portions of the tree.

Figure 1. Mature spindle requires attention to the upper canopy.

Figure 2. A spindle pruned for better light penetration into the canopy. The top of the tree has had a good thinning. Without this pruning process in the dormant season, fruit colour and bud size through the lower part of the canopy will diminish rapidly.

Related Links

• Training and Pruning Apple Trees, OMAFRA Publicatin 814