Down Garden Services

Indoor Plant Care Information for homeowners, garden centre personnel, and plantscape technicians.

Pruning

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 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.
If a shrub is growing unevenly logic would dictate that the excess growth should be removed, but this 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.

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 surgical 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 as overheating the blade 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.

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.

Pruning Shrubs

Timing is very important, especially with flowering shrubs as the future blooms can be removed.

A general rule of pruning is to prune just after flowering so the plant has time to grow new shoots that will flower in the following year. If the plant blooms before June the flowers are usually from buds produced the previous year, but if it blooms after June the flowers are usually on new growth produced in the current year. Forsythia is a good example where non-flowering is caused by inappropriate pruning, it is a vigorous grower and the temptation is to trim off all of the outer shoots (the sort of pruning done using a hedge trimmer). It blooms on the growth from the previous year and this removes all of the flowering buds, so the best way to keep it to a reasonable size is to remove complete branches from lower down in the plant. In the case of Forsythia the older branches tend to be 'pimpley' and there is usually different coloured or textured bark on older shoots of many shrubs.
This brings us to another rule for pruning shrubs. Choose one third of the oldest branches and prune them near to the base of the plant. This means that the whole bush is renewed every three years and it never grows to more than the height it can reach in this period. This is the method used for most shrubs, but as with any rule there will always be exceptions and Buddleja davidii is one such plant where all of the branches are cut back close to the base every year to keep a compact bush. Any vigorous, late-flowering shrub which blooms on growth produced in the current year can be cut back hard, eg. Fuchsia. All of the branches of colour-barked Dogwoods are removed close to the base to allow fresh shoots to be produced.

If the prunings are of a reasonable length they can be used as plant supports. Let them dry off for a few weeks otherwise some of them may take root. Good subjects for this are Dogwood and thinings from Willow, Birch or Beech.

Pruning Trees

Most gardens only have room to accommodate one or two trees, and even these have to be species which do not grow into large specimens. It is better to prune out some branches when they are small, than to wait until they are an obvious problem. This can save the expense of hiring a specialist contractor and keeps the tree in a naturalistic shape without ugly scars where large branches have been removed.
Stand back from the tree and decide the height where the canopy should begin, then remove any branches below this point. Always make a shallow cut underneath first to prevent a long tail breaking away pulling bark with it.
Now consider the canopy and thin out the branches to leave them evenly distributed, cutting close to the origin so that there are no snags left which will die back and could attract diseases such as Coral Spot. If further thinning is required, cut at a fork in a branch, removing the longest growth.
When removing large branches take off most of the outer growth first to reduce the weight, then cut the main stem about 30cm from the base. The final cut is made close to the origin, cutting underneath about half-way through, then from the top - there is usually a slightly raised collar on the trunk around the base of the branch which defines the line where the cut should be made. Pare off any frayed edges with a sharp knife. If the tree is prone to disease use a wound sealant which contains a fungicide.

  
Cut back to the natural 'collar' which will grow over the wound to seal it.

Keep standing away from the tree during the process and look over your work to pick the branches to remove. The canopy should be open without too many inward-growing branches or ones which rub against another. If possible catch hold of the target branch and shake it to see the space it is occupying, this will give a clue to how its absence will look.
Trees are usually pruned in late autumn or winter when the sap is down to prevent 'bleeding' from the cuts. Also pruning when the leaves are absent makes it easier to see what you are doing, but there are exceptions. Any of the stoned-fruit trees, eg. cherry, plumb, almond, peach, are prone to a disease called Silver Leaf which enters through wounds, so they are pruned in the summer when the sap not moving as much and there are fewer spores around. Although this is also when they are still carrying their fruit, removing some of it will improve the remainder and the branches would be missing the next year anyway.

Hedges

Cutting a hedge is multi-pruning to a uniform shape. The ideal profile of a formal hedge is to have a slightly outward slope or batter towards the bottom which allows more light to reach the lower branches - usually referred to as an A-shape. A hedge of this shape is also able to better withstand strong winds and a heavy snow-fall is shed more easily. As a new hedge grows it should be lightly trimmed to promote plenty of side-shoots and form a dense structure. To obtain a straight top, a string can be stretched along at the correct height - this is very useful on a slope or undulating ground where it can be difficult to judge. The recommended method of obtaining a uniform slope to the batter is by using a lath with a cross-piece which rests horizontally on top of the hedge - like a large angle gauge.
It is easier to achieve a level finish using an electric or petrol driven hedgecutter. The 'teeth' of the cutting bar should be angled slightly downwards so that it removes enough of the growth, otherwise the hedge has a tendency to expand each year.
When using an electrical hedgetrimmer the cable should be draped over the shoulder to keep it safer. There is a new type with a rotating blade and a clipping collector, but it can only cope with fine shoots and has to be used quite frequently.
Small-leaved plants make the neatest formal hedges and produce the best finish with frequent close cutting. Large-leaved species such as Prunus laurocerasus (Cherry Laurel) should be pruned to shape with secateurs for the best result otherwise the severed leaves develop a brown edge or die back completely. Griselinia litoralis (New Zealand Privet) may also be treated this way, but this could be a bit tedious for a long run of hedge.

Hedges can also be informal where they are made up of various species of shrubs which are pruned to a natural shape at different heights. Also by following the methods for pruning shrubs, flowering species can be used to full effect. To have a flowering formal hedge such as Escallonia it has to be allowed to produce quite long shoots which may look untidy - they are removed immediately after flowering to allow new shoots to develop for the following year.

The most controversial hedging plant is XCupressocyparis leylandii (Leyland Cypress) and its golden forms which are very fast-growing and can become very dominant. They can be kept to a reasonable height and form a dense hedge, but must be cut at least twice a year to remain tidy. It is important to stop the upward and outward growth when it has reached a height which can easily be reached for this regular cutting as they cannot be reduced beyond the green growth - they do not resprout from bare stems. The tops should be stopped about 30cm below the final height, then allowed to fill out the uneven spaces. It is possible to have a normal-sized hedge of these plants, but there is a gradual outward and upward spread.
Where a hedge has become too large, most species can be cut back very hard and they will produce new growth. To reduce the height cut down to about 30cm below the final height - this will work for Conifer hedges provided there is plenty of green growth remaining below this level. It is not possible to reduce the width of a Conifer hedge beyond the green growth, apart from Yew (Taxus baccata), which will regenerate from a stump. For most other hedging, reducing the width is carried out over a two year period, one side is cut back close to the underlying upright branches the first year. The following year when the first side has produced lots of new shoots, the process is repeated on the other side.

Always check around the base of the hedge for seedlings of Brambles, Ivy and tree species such as Ash, Sycamore and Elder which will take over the hedging plants, making it very untidy and may kill parts of it off. If this has occured prune out the weed species gradually, allowing the hedging plants to fill the spaces - it may take a few years to achieve if the interloper has been allowed to thrive.

Pruning Roses

Shrub roses require annual pruning to keep them compact and to promote new growth. For larger specimens two prunings are usual, the first in late autumn when most flowering has ended to reduce the height and prevent rocking by winter winds. The more accurate pruning is carried out in early spring, and recently this has been earlier than is mentioned in most gardening books due to the milder winters.
Any dead or diseased branches are removed then the remainder are cut back to an outward-facing bud - this can be quite small and is marked by a horizontal line left by an old leaf scar. Inward facing, and weak branches are usually removed to give a better shape and allow a good flow of air to prevent diseases. Recent thought is to leave the finer branches as although they are unlikely to carry flowers, their leaves produce valuable nutrients. Pick off any remaining leaves with Blackspot disease - pruning the stems hard back removes most of the lesions which might be on the bark.
A recent practice is to use a hedge trimmer to do the initial cutting back and tests have shown that without any further detailed pruning, flowering has been just as good if not better. This may work for a few years, but the bushes would become congested and may be more prone to disease.

Climbing roses grow to less than 3 metres and have to be trained to obtain the best show of flowers. Left untrained, branches grow upwards and produce a small number of blooms near to the top. To encourage more blooms the branches have to be trained horizontally along wires or on trellis. This changes the balance of the growth hormones causing lots of side shoots to grow and these will carry more flowers. Allow a number of branches to develop and bend them sideways when they are young and pliable, tying them in at different heights. Each year cut out some older branches at the base and tie in the new ones, to maintain a succession of growth. Older roses can be rejuvenated by cutting out the older main stems near to the base to force new ones to grow, do not remove all of them as the shock may be too great.

Rambling roses grow to more than 3 metres in height and are not usually pruned except to keep them within the required spread, but they can be treated in a similar way to climbers if a more controlled display is required.

Standard roses are not so common now, but are treated like bush roses, except they are on a stem with an elevated grafting point.

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