Pruning is a means of maintaining tree vigour, improving structural soundness, and enhancing live-ability. Pruning is the process of removing dead branches and stems, removing branches that are structurally unsound or will in the future cause structural problems, and taking into consider- ation overhead wires, buildings, vehicle and pedestrian traffic and thereby making it easier for people and the tree to live in harmony.
Most deciduous ornamental trees (poplar maple, elm, willow) should be given a through pruning every three years and minor “touch up” pruning annually. A through pruning involves removing dead limbs, crossing branches (or branches that will cross in the future), overhead line clearance (when safe to do so), pruning limbs off roofs. Most large trees can be pruned any time of year. Exceptions to this are birches and maples which will bleed sap unless pruned while in leaf. A further exception to this rule are northern elm trees which may not be pruned between April 13 and July 31. This is to help prevent the spread of Dutch Elm Disease. If possible avoid fall pruning as many types of decay fungus spores are present at this time. A “touch up” pruning involves the removal of suckering growth, and dead and diseased wood.
Fruit trees often need an annual pruning and are typically pruned before leafing out in the spring. Prune to control top growth, and let light into the centre of the tree. Ideally fruit trees are pruned to a low and wide form. This eases picking and maximizes light penetration. Proper disinfecting of pruning tools is an important part of pruning of fruit trees as many diseases may be spread by contaminated saws and clippers.
Coniferous trees (spruce, pine, fir, cedar, juniper) do not take well to pruning and should be allowed to maintain their natural shape. When growth starts in the spring, up to two- thirds of the new growth may be safely removed to control growth. Coniferous trees don’t regrow cut branches, and needles only remain on a tree for about five years. The natural pyramid form of spruce and fir tree is destroyed by top removal in any attempts to control vertical growth.
Positioning of Pruning Cut
Formerly people were encouraged to remove a tree limb by making the pruning cut flush with the tree bark and in many cases this is OK. Flush cuts can possibly cause structural damage to the tree, and sometimes do not close properly thus providing an opportunity for infection and decay to infect the tree.
The current method often advised is to locate a pruning cut is at the point at which a tree limb is naturally lost. Look at the point of attachment of a branch and a main stem meet. There is usually a swelling, particularly on smaller branches. This swelling is called the “branch collar”. When using clippers or a handsaw, pruning cuts should be made directly outside of this swelling (ie. towards the end of the branch). Larger branches may not show signs of this swelling, but on the bark of the tree there is an line defined by an area of raised bark centred in the branch crotch. A pruning cut to remove a larger limb should be made on branch close to but not cutting in to the trunk, and parallel to the line created by the raised bark.
When cutting with a chainsaw, the position of the cut is a point mid-way between the branch collar and the branch bark ridge. The cut is made by starting at the top of the branch collar and cutting straight down. Sometimes a cut is made under the limb first to prevent bark stripping when the limb falls.
Some Basic Rules of Pruning
1. Remove dead and diseased wood.
2. Remove structurally unsound wood (crossing and rubbing branches.)
3. Remove less than one third of the foliage bearing wood.
4. Try to avoid cuts greater than 15 cm in diameter.
5. Never leave a stub that is incapable of further growth (ie. no branches or buds.)
6. When making a “stubbing cut” to control lateral growth, cut back to a branch at least one-third the diameter of the branch removed.
7. When removing a dead top, cut back to a limb that can assume the role of a new growing top.
8. You do not usually want to not top a tree to control height.
9. Target pruning cuts to the branch collar.
10. Pruning paint may only be effective in prevent desiccation of large pruning wounds.