Pruning inevitably damages plants. When done properly, however, the wounds will seal over quickly and completely. Proper pruning also reduces the risk of rot caused by invading microorganisms. Hence the importance of knowing where and how to prune.
Removing a branch near the trunk
When cutting off a branch near the trunk, it is important not to remove the branch bark ridge or the branch collar.
Flush or close cuts should be avoided, as should cuts too far out, which would leave a stub (the broken or cut base of a branch projecting from a tree trunk).
A stub prevents woundwood from growing fully over the pruning cut and provides an entry for microorganisms, fungi and insect pests.
The cut should be clean and straight, on a slightly oblique angle, at about the same angle to the trunk as the branch bark ridge. This sort of cut will allow woundwood to form around and gradually over the cut. It will also help keep rainwater from accumulating.
Special case: removing a large branch
Branches larger than 4 cm around should be removed in three stages to prevent them from tearing any of the trunk tissue as they come off.
- Make a cut on the underside of the branch, about 30 to 45 cm from the branch collar. Cut only one-third of the way through the branch.
- Make a second cut on the top side of the branch, about 5 cm farther out on the limb. The limb will fall when the two cuts meet.
- Remove the remaining stub, cutting it at the angle described above.
Trimming back a branch or twig
When trimming back a twig (3 cm or less in diameter) or a branch, directional pruning is always best. This encourages the pruned twig or branch to grow in a desirable direction.
To trim back a twig, cut it on about a 30° angle, a few millimetres above a lateral bud. Always cut a branch back to a side branch, being careful not to damage the branch bark ridge.
The bud or side branch acts as a sap drawer, redirecting the sap while discouraging water sprouts. In addition, the sap flow around the wound will cause it to seal over more quickly. The diameter of the sap drawer must be at least one-third that of the pruned branch, or it could dry out.
There is no need to apply any dressing (oil, paint, gum, etc.). Such products can even be harmful to plants, by creating conditions that encourage insect pests and disease. Because woody plants have their own defence systems against pathogens, it is best to leave pruning wounds exposed.