The Essentials of Tree Pruning

Tree pruning is often not well-understood by home gardeners and trees can be damaged by poor pruning techniques. This month we asked Dr Greg Moore to give us some brief guidelines on the essentials of tree pruning.
The first thing to remember is that we only prune ornamental trees when we have to and then we do what we can to minimize the size of the wound. This is to reduce the risk of infection from disease or decay. Wounds on trees do not heal but grow over and our objective is to facilitate the growing over process as best we can.
When a limb is being removed from a tree, we look at the point at which the limb joins the main trunk. The swelling at the base of the branch is called the collar and it is important that pruning cuts are never made into the collar. Instead we cut to the outside of the collar. Often the collar is difficult to see. In these cases we use the branch bark ridge (BBR) as our guide. Every branch has a BBR and this can be seen by noting the change in the angle of the pattern on the bark of the branch compared to the pattern on the main trunk. We make the cut on the branch at the same angle as the BBR.
Another essential technique is to first make a cut on the underside of the branch that is being removed. This cut is made to prevent the bark ripping and tearing as the limb drops. Tearing can open wounds which make it easy for pathogens to enter the tree and hampers growing over.
In the past, gardeners were advised to prune the canopy of trees when they were transplanted to compensate for the loss of roots during the transplanting process. Today we understand that trees need as much foliage as possible to photosynthesise to facilitate the growth of new roots and pruning at transplanting is only recommended where water is the limiting factor. If you keep water up to the tree during the establishment phase, then you will get a much better result if you do not prune the canopy at all when you transplant.