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 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 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. Flush cuts have be shown to cause
structural damage to the tree, and do not close properly thus
providing an opportunity for infection and decay to infect the
tree.
The
current method 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.
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.
Do 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. Paints do not prevent decay or stop sap
flow.
