Reasons for pruning
Trees may be pruned to improve health, safety and the aesthetics of the tree. The following are reasons for pruning:
Diseased, damaged or dead wood
Remove crossing branches or damaged wood
To improve the shape of the tree
Improve quality and production of flowers and fruit
Encourage new wood
Improve access and/or views under the canopy
Improve light levels and air circulation under and through the canopy
Eliminate structural weakness
Reduce the tree size
With small branches it is best to cut as close to the union as possible, without leaving stubs or damaging the adjoining branches.
With larger branches firstly look for a collar. A collar is the ‘swelling’ at the union of the trunk and a branch, which occurs on most species. If this can be seen make your final cut where the collar finishes on the branch, without leaving a stub or cutting into the collar. To provide a protective barrier against insect and disease attack, it is important not to remove or damage the branch collar region.
If a collar cannot be seen then look for the branch bark ridge. This is an area of tissue thinner than the collar between the trunk and the branch.
Correct cuts for pruning
If the branch is removed according to the above method, it gives the tree a better chance of healing the wound itself. This can be seen by ring of growth cells covering the wound from the outside in.
This formation can be a slow process, depending on the species, but the cells protect the tree against insect and disease attack, with entry via the wounded area.
Look for the collar of large branches
When pruning large branches, the correct pruning technique requires three separate cuts performed in the following sequence:
1. The under cut
This is made 1/3 of the way through the branch, to remove the heavy weight from the branch and it will prevent the bark tearing.
2. The top cut
This is made approximately 10 cm away from the under cut, and cut the entire way through the top of the branch. There is now a stub left.
3. The final cut
The stub should be removed and care must be taken not to leave a stub, or to cut too close to the trunk as shown in the diagram.
The healing process
Flush cuts should not be made because the cells responsible for healing over the wound are removed in the process of a flush cut.
Therefore the doughnut-shaped cells do not cover the wound, and the site becomes an easy access point for disease and insects.
Avoid flush cuts
Often branches are heavier than they appear, and you may often think the three cut pruning method is not necessary and more time consuming. It is on these occasions that you misjudge the weight of the branch, and the bark or branch fibers rip down the trunk before the cut is complete.
This scenario causes the same effects as a flush cut as there is often a large wound area, and the healing cells have been damaged or removed.
In the past wounds were treated with special paint or cavities were filled with cement. Presently wounds are not treated with chemicals because if pruned properly the tree is capable of healing itself.