Indoor Plant Care
Information for homeowners,
garden centre personnel,
and plantscape technicians.
Shrubs Trees Hedges Roses
Pruning a tree or shrub is carried out to improve the shape, encourage better flowering or restrict the size. The majority of trees and shrubs which are planted in the average garden soon outgrow their allotted space if they are not controlled in some way. When planting they are usually placed too close to each other and even smaller specimens soon become overcrowded as many of them in their natural habitat would grow to fill an area the size of some gardens, so to have a variety of shrubs some can be removed to make room, but usually they are pruned. To maintain a roughly natural look it has to be done carefully and preferably started before the plants become overgrown. Anticipating where branches are likely to end up and removing them at an early stage will produce a better looking plant, reduce the size of the scars and the chances of disease entering.
There is a great mystique about 'the correct way to prune' and many people approach it with trepidation. By following a few basic rules the desired effect can be achieved, but there is more to it than chopping off the unwanted limbs at random.
The equipment required is not extensive for most tasks; secateurs and loppers will usually suffice. A good pair of gloves is recommended and for very thorny specimens such as Pyracantha welding gauntlets, which are made from split cowhide, are inexpensive and effective - also when feeding prunings into a shredder. For thicker branches a pruning saw fits into narrow spaces and the cutting action which usually works on the pull stroke, is very effective
The growth of plants is affected by a number of factors - the obvious ones being nutrients, light and water. As well as increasing or decreasing the amount of nutrients applied to a plant the growth rate of a tree or shrub can be altered by the removal of branches or roots at particular times. If the branches are pruned in summer when they are producing food, then less will be available for storage to grow shoots the following year. This explains the choice of summer or winter pruning of fruit trees - to keep cordons in check they are pruned in the summer. When some of the top-growth is removed the roots which nourished it are still in place so the plant can soon replace it. This is used to advantage when pollarding or coppicing a tree. The vigorous regrowth is not always desirable, particularly when training fruit trees. In the winter the roots of a tree can be pruned to prevent stored starch being taken back up to produce unwanted growth. Another technique which used to be popular is ring-barking where a section of the bark is removed, thus preventing the descent of sap for storage in the roots.
The growth of plants is controlled by the release of special chemicals or hormones, which affect the rate of cell division and elongation. For example if light is restricted to one side of the plant the cells on the opposite side of the stem receive more of the growth hormone promoting division, bending the top, and therefore the leaves, towards the light.
There is also an influence known as apical bud dominance. In this case the apical or topmost bud is producing lots of auxins to allow it to grow and some of it is carried down in the sap where it suppresses growth in buds lower down the stem. If the apical bud is removed this influence ends and the lateral shoots begin to grow. This is an important factor to remember when pruning as it can be used to promote the required growth when training a shrub or tree.
Sometimes when a tree or shrub has become overgrown the bottom will be bare so some new branches might be desirable. There is a technique known as 'notching' which can be used to encourage new growth. The apical buds will be inhibiting such growth with auxins which flow down in the sap. By cutting a notch in the bark above a dormant bud it should break into growth. A dormant bud is usually where a leaf once grew so making a v-shaped cut a few millimetres above the bud will interupt the decending hormone - it must not be more than a third of the circumference of the stem, but usually it is much less.
When the new growth develops the upper branches can be reduced as they could block light and the new branch may not grow well. If a tree or shrub is growing unevenly logic would dictate that the excess growth should be removed, but the removal of the apical bud will cause the smaller shoots further down the pruned branch to burst into growth. By pruning out some of the shoots on the shorter side their apical dominance is removed, so more growth is promoted. There are probably reasons why there is unbalanced growth such as a lack of light or exposure to the wind so there may always be a tendency for the imbalance to occur.
Notch above a dormant bud.
After a few weeks the bud breaks.
A way to reduce the growth of branches is a technique called 'nicking' where a similar cut is made in the bark below the point where it emerges from the trunk. This interrupts the flow of growth hormones up from the bottom of the plant.
Hygiene is an important consideration and any tools used should be disinfected after pruning infected material or before pruning plants such as fruit trees which are prone to disease. This can be done by swabbing the blades with methylated spirit or by playing a flame over them - a cigarette lighter is handy for this. Do not use a strong flame such as a blowtorch close to the blade as overheating it will remove its 'temper' and it will not keep its sharp edge.
On trees which are prone to disease any cut larger than the capacity of loppers, requiring a saw, should have ragged edges trimmed smooth and treated with a wound sealing compound. It contains fungicides which should fend off an attack until the plant starts to heal over the scar naturally. It should be applied within a few minutes as the spores of diseases can be in the air or raindrops.
As well as controlling vigour or changing the shape of a shrub or tree, pruning can be done to improve the health of the plant by allowing better airflow. Also developing fruiting or flowering spurs is achieved by careful pruning.
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