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Pruning Wisteria and some shrubs

Our Garden Design Forum has proved to be a very popular way in which gardeners can ask expert garden designers for advice and tips. This page contains some short articles from ourselves that have been sent to customers as part of our advisory service and that we feel should be an integral part of our Garden Design Forum. Where we have found articles by other professionals that we believe can help you, we have also included a link.


Page One - Pruning

  1. Pruning Wisteria

Pruning Wisteria

Planting wall shrubs and climbers

After preparing a planting hole 3ft (1m) square and 9in (23cm) deep, and adding organic material to a further 9in (23cm) of depth and to the soil removed, the plant should be planted 15-18in (40-50cm) away from the wall or fence and leant back towards it. This is done to ensure that the plants are not starved of moisture as is often the case when they are planted closer to a wall.
The foundations of walls absorb moisture and, like fences, deflect rain away from their bases; the 12in (30cm) of soil surface directly below the wall or fence can become very dry at any time but particularly in the spring and early summer, both critical times in plant establishment and growth.
We want, and expect, climbers and wall shrubs to reach substantial heights, but without constant moisture this is not possible. As the plant grows it will also gain stem girth at the base and if planted too close to the wall or fence this may be restricted or damaged.
In some cases it may not be possible to prepare a round or square hole because of paths or other obstructions in close proximity to the proposed planting position. In these cases the hole can be dug lengthways along the wall or fence until the recommended square yard (square metre) per plant is prepared. In some cases it may be possible to remove a paving slab or cut away the obstruction; even realigning the path might be worth consideration.
Should none of these alternatives be possible, then excavating under the obstruction and infilling with prepared soil may be possible but care should be taken not to cause subsidence.

Pruning

Possibly the question most asked by the gardener is how to prune a Wisteria to make it flower. Before this can be described fully, one or two points must be explained and possibly the most important is the selection of the right Wisteria plant in the first place.
Wisteria grow very easily from seed but regrettably the resulting flowering, often some eight years after planting, is very variable, not only in the time they take to flower but in size and, more importantly, colour. Plants raised in this way should be avoided, even though they appear less expensive than the alternative, more reliable, grafted varieties.
To add to the confusion, even the basic form, Wisteria sinensis, may be grown from seed to grafted, and the only way to be sure is to purchase a grafted named variety or to ask the supplier which propagation method was used, if he does not know, do not buy.
Next the growing aspect: it is important that Wisteria is given a south or west facing position, for without it the shoots will not ripen and flower buds will not be formed.
You may have a newly planted Wisteria, say up to one or two years old, or a well established Wisteria, planted some years ago but never pruned and somewhat out of control - a very daunting pruning task. Although the two ages require different pruning, the aim in both is to achieve a vine like shoot formation on which the flower buds will form over the are allowed for its total maximum growth.

Pruning a newly planted wisteria

In the late mid to late spring following planting (which should have been, most importantly, carried out as recommended in Chapter 1) pruning can start - or, more rightly, training can begin. A formation of horizontal shoots at regular intervals growing out from a central upright main shoot is the aim.
Even though it may seem harsh and it will appear that the height of the plant just purchased is being cut away, in early to mid spring of the year following planting the main shoot is cut back to within 18in (50cm) of ground level. Should the plant have more than one main shoot then choose the strongest and remove the remainder completely. If the main shoot is not 18in (50cm) tall then just tip it, removing the terminal bud, but in all cases cutting it is important to prevent it from becoming dormant and shy of growing.
Normally when the plant is supplied it will have at least a 3ft (1m) bamboo cane supplied with it, which should be replaced with a 6-8ft (2-2.5m) one, and this should be tied to the horizontal support wires with soft fillis twine using a figure of eight knot (see Chapter 3).
In the spring and summer following the first cutting back at least one strong upright shoot will develop and as it grows it should be tied to the cane. If more than one develops the strongest is chosen and the others removed. By early summer the chosen shoot will have reached 6-12in (15-30cm) above the first training wire and is stopped at a bud 3-6in (8-15cm) higher than the wire. If it has not reached the first wire, pruning is best left until the spring of the following year.
From below the point at which the shoot is pruned a number of shoots will emerge. The first of these is tied vertically to the upright bamboo cane. The next two are tied left and right along the first horizontal training wires, and any surplus shortened back to 12in (30cm) in summer and then in winter reduced again to two buds or 2-3in (5-8cm) from the point of origin.
Should side shoots be formed off the selected horizontal shoots, these also should be shortened back to 2-3in (5-8cm) in the summer and winter; it is from these shortened back shoots (spurs) that the first flower buds will form for display in future years.
Depending on the weather and soil conditions the stopping of the central upright shoot may be required again once it reaches the next wire, and the resulting shoots should be tied in and trained as for the first wire.
In year two the plant is allowed to grow on until it reaches 6-12in (15-30cm) above the next wire, when the process is repeated. By now it may have gained enough root development to reach a number of the wire levels, and at each it is stopped and trained as before.
As the side shoots grow along the horizontal wires they are tied in and any surplus shoots on the main or side shoots are cut back in summer to 12in (30cm) from their point of origin, and reduced further in the winter to two buds or 2in (5cm).
In year three the same procedure is followed, shortening back the main shoot when it reaches the upper wires or possibly the full height required. The side horizontal shoots are tied in and any surplus pruned as before.
The main framework has now been formed and only the horizontal side shoots will require further training and tying in.
Normally from year four onwards the Wisteria will be in flower, but without the training suggested it could be at least eight years and often longer before it comes into flower.
Routine training and pruning can now start and will be covered after the explanation of the pruning for an out of control Wisteria.
Always tie the shoots of the Wisteria to a bamboo cane or wires using soft three-ply fillis twine and the figure of eight knot described in Chapter 3.

Pruning an out of control and overgrown Wisteria

A Wisteria may have become overgrown from neglect, apprehension of causing damage or the sheer size of the problem. With the right approach the plant can be brought back into full flower production and generally have its appearance improved, while at the same time bringing it under control and reducing the work required in the following years.
At the first inspection there will appear to be a maze of intertwining shoots that form no real pattern and first task is to identify the ones that will form the main framework. Ideally this will be one major central shoot but ore often two or even three have to be selected due to the lack of previous pruning and training. Care needs to be taken to locate any dead or partially damaged shoots that have been strangulated by the intertwining shoots or bad tying-in, and these are not always clearly visible at first sight.
As the pruning progresses, training wires, if non-existent or in poor condition, will need to be provided or replaced (see Chapter 3).
Starting at ground level and working upwards, the main shoot or shoots are tied to a 6-8ft (2-2.5m) cane, which in turn is tied to the support wire. In some cases this may be of a temporary nature until the pruning is complete. As suitable side shoots growing off the vertical shoot are located, they are tied out on to the horizontal wires. This may entail lifting, lowering or bending some to fill a particular position.
Any surplus side shoots are cut back to 12in (30cm) of their origin in the summer and further reduced to 2in (5cm) in winter. The process continues until the full height of the plant is reached. The selected side shoots are also trained and tied out until they cover as much of the area as required.
In some cases the pruned Wisteria may not cover the same area that it did before pruning but it will quickly make up any deficit in the following spring and summer as new side growths are formed.
A great quantity of surplus shoots will be removed but the pruner should not be alarmed.
The work can be carried out in late summer and autumn but as long as there are no hard frosts it can also be done in winter, and often this is the best time as the shoots to be retained or removed are more clearly seen.
The Wisteria is now ready to receive routine annual pruning.

Routine annual Wisteria pruning

From the main stems and horizontal side shoots, through spring and summer, numerous side shoots (tendrils) will grow and it is the shortening back of all of these, each year, that produces the flower buds for future years.
Therefore the more shortening, the more flowers, but it takes upwards of two years for the remaining buds to form into flower buds. As the shortening is practised every year, 'flowering spurs' are formed, and care must be taken to ensure that these are not damaged in any way.
The pruning or shortening is best carried out in two stages, first reducing them to 12in (30cm) long in midsummer or late summer, and then finally to 2-3in (5-8cm) or two to three buds in winter at any time as long as the weather is not too cold. It should then be done annually.

Wiring the walls or fences

The best way to support a wisteria is to provide it with wires.
To achieve this first use 4in. long screwed vine eyes. Wherever used they should not be more than 6ft apart and always in a straight line. In houses older than 1950 it may be necessary to secure into the bricks. After this time most mortar courses can support the vine eye.
Place the first line 18in from ground level with additional wires every 18in or so. Supplying wires at 18in spacing until the top of the wall is reached. With Wisteria insure any wire above a door or window is 18in above it.
The wire can be galvanised or plastic coated. It should be thick enough to take the weight of the plant but also flexible to work with. Hardware shops and farm supply outlets are possibly the best places to find both wire and vine eyes.

Pruning knives

A good quality pruning knife will be required, to remove thin weak shoots as well as to pare, or smooth off, the edges of pruning cuts that are larger in diameter than your thumb. This is done to assist the healing process and seal the cuts by aiding the production of a layer of new tissue by the growth cells in the cambium layer just below the bark. Once formed, this growth barrier can keep out infections such as canker on Apples and Pears, silver leaf on Cherries and Plums and fireblight on Cotoneasters.
In addition, Heal and Seal pruning compound should be applied to protect the cut from attack by fungus diseases such as coral spot. Whereas some would argue that this is no longer required, I believe it is particularly important on slower growing ornamental trees, shrubs and climbers.

Secateurs

For larger cuts, Secateurs will be required and these come in two types; parrot bill, where the upper, sharpened cutting blade cuts down across the lower, unsharpened, anvil blade; and anvil, where the thinner, sharpened upper blade cuts down on to the lower, thicker and wider, unsharpened anvil blade.
It is said by some that the normally more expensive parrot bill type makes a better cleaner cut and prevents bruising of the stem, but I have found that if both types are well maintained and kept sharp, there is little difference, except for the higher price of the parrot bill type.
However, the following rules apply to both types to ensure a good clean cut and prevent damage to the Secateurs. Firstly the upper, sharpened blade should always be on the top or front side of the cut so that the cut is made smoothly downwards or forwards and with the minimum of sideways movement. Secondly it is important never to attempt to cut material that is too thick; never try to cut shoots thicker than can be fitted between the blades when fully open and never nibble or attempt to cut a branch in stages from different sides. Also, never force the cut by placing sideways pressure on the Secateurs, as this is a major cause of permanent damage to both types of Secateurs.

Long-handled loppers

Should the shoots be too thick for Secateurs it will be necessary to use a pair of long-handled loppers, which have more leverage. These also come in two types, parrot and anvil, and the same rules of use apply as for Secateurs.

Folding saws

As an alternative to loppers, and in some cases Secateurs, my choice is to use a folding pruning saw; I find that with its 6-9in (15-23cm) blade it not only cuts the larger material and does it very cleanly, but because of its narrow and short blade it can reach into difficult confined spaces.
As it cuts on both strokes, backward and forward, care must be taken, as always, to prevent accidents from the very sharp teeth.
A good sharp folding saw can make as clean a cut as the best Secateurs.

Bow saw

There may be times when the folding saw is not adequate for the job, and then a bow saw will be needed. Although it can sometimes be difficult to position due to its size, it is useful for the removal of larger branches, particularly on trees.

Chain saw

I advise strongly against using a chain saw, for not only can it be very dangerous when used by an untrained operator in confined spaces, but if used indiscriminately it can cause a great deal of damage to the tree or shrub being 'pruned'.

Sharpening of pruning tools

All tools should be kept clean and sharp, and if a lot of work is carried out in the garden each year, replacement tools, in particular Secateurs, may be necessary. The sharpening of knives and Secateurs is best done using a household or workshop chisel sharpening stone, which can be purchased from most DIY stores. It will normally have hard and soft sides and will be 4-5in (10-12cm) long, 1in (3cm) wide and ½in (1cm) thick. Before use it should be moistened with water or a small amount of household oil. The cutting edge of the blade is drawn, three or four times, slowly and firmly over the stone at an angle of 25-35°, ensuring that the bevelled edge of the blade is facing down on to the sharpening stone. To finish off, one pass is made over the stone on the reverse side to remove any 'burr' - the small pieces of metal that may have formed.
If this sharpening process is carried out with a new knife or Secateurs, the soft or smoother side of the stone is used. Sharpening should then be repeated at regular intervals during use.
Should the knife or Secateurs have been neglected, three or four passes over the hard or rough side may be best, finishing off with two or three passes over the soft or smoother side, plus the reverse pass. If more than this is required it is probably best to purchase a new tool.
Loppers do not normally require sharpening, but from time to time passing the hard or rough side of the sharpening stone over the leading edge of the cutting blade may be of assistance and will help with the final cleanness of the cut.
Saw blades are best replaced as necessary, as to have them sharpened could cost as much, even if you could find somebody to do it.

Making the pruning cut

Whenever possible, cutting to above a bud is recommended. Buds are normally the raised points along a plant's shoots where the new side shoots, leaves and flowers will be produced. They may be arranged opposite each other or alternatively along the length of the shoot, normally at regular intervals. They contain all the plant's potential for producing new side shoots, foliage and flowers in the spring, summer and autumn following pruning, so care is needed to avoid damaging them.
When the plant is, say, more than three years old, the buds may be harder to see, having become camouflaged by the bark. But even if they cannot be seen, they are still there in a dormant state and once pruning has been carried out they will be induced to grow and produce new growth. When pruning, a calculated guess may have to be made as to their position.
If the buds can be seen, the cut should be made above and within ¼in (5mm) of the bud. If the cut is not made cleanly or at the right angle, there is always the chance of dieback; this is caused by rain entering through the pruning cut and inducing rotting, which can spread and cause further damage. Alternatively it can be caused by the pruning cut being made too high above a bud so that plant foods in the form of sugars are not used and all the surplus food above the bud will rot. Once the fungi have a hold, they spread down the stem in search of more food and start to kill the plant tissue in order to obtain food in a form they can use. With some species of shrubs, in particular Acers (Maples), coral spot fungus may gain a hold under these conditions, as will cankers of various trees in the Malus (Apple) family.
So a clean cut is made with a sharp pruning tool at an angle sloping away from the bud to ensure the run-off of rain, and just far enough above the bud to avoid it being cut or crushed. If the cut is larger in diameter than your thumb, it should be pared off (the edges of the cut trimmed) with a sharp knife and painted with Heal and Seal to prevent the entering of diseases.

Tree-pruning hygiene

To prevent the build-up of over wintering pests and diseases the application of a winter tar oil wash is good garden practice, to eliminate the eggs and spores of the pests and diseases that attack and spoil fruit. The wash also improves the appearance of the bark of trees or bushes by making it shine and for this reason it is very effective when used on ornamental trees as well as fruiting varieties.
The directions on the product should be closely followed and health and safety requirements complied with.
Personally I am not in favour of shredding pruned shoots, as there is always a risk of spreading pest and disease infestation, nor do I like to use the shredded material for soil mulching or improvement, for the reason stated in Chapter 2. All pruning material should always be removed and burnt as soon as possible.

Removing large shoots and branches

If a large shoot is to be removed using a saw, folding or bow, it is good practice to make the first cut 2ft (60cm) away from the intended final cut, so removing some of the weight. To help make a clean final cut, approximately a third of the diameter of the shoot is cut with the saw from the underside upwards. A cut is then started from the top, ensuring it is in line with the lower one, and the remainder of the cut made.

Geographical differences in pruning times

Throughout the following text, reference is made to the timing of pruning, based on the southern and central area of the United Kingdom. For those gardening in the southwest, the work can often be brought forward by seven to ten days. In the north, Northern Ireland or Scotland, it may need to be delayed for a week or two, but in all areas, account should be taken of weather conditions, and if in doubt wait until the weather improves.

Tying materials

It seems that whenever industry produces a new or waste product that might be used as a tying material, particularly if it is coloured green, it is offered to gardeners without any tests being done or consideration being given to the damage it may do to a plant by strangulation.
With the possible exception of perennials, all plants require ties that can expand, can be adjusted or will rot within a year to prevent damage.

Recommended soft tying materials

  • Three-ply fillis string (untreated)
  • Raffia, although this is more expensive than fillis string
  • Small and large adjustable rubber or flexible straps, ensuring the size is adequate for the tree and that all are supplied and fitted with a buffer to avoid rubbing between the tree and stake; whenever possible, purchase the straps loose rather than pre-packed, as they are often cheaper.

Tying materials to avoid at all costs

  • Polypropylene string
  • Binding twine
  • Wire
  • Plastic tying material that does not stretch as the plant grows
  • Rubber and plastic ties of the interlocking chain type
  • Fillis and other soft strings and twines that are treated with creosote or green tannalized to prevent rotting.
  • Modern tights and stockings produced from material that does not rot.
  • Figure of eight knot

Over the years I have tried a number of different knots and ways of attaching plants, other than trees, to their supports, but the safest and most effective way has always proved to be the figure-of-eight knot where the fillis string is looped around the cane, support wire of individual anchorage point, crossed over itself, looped around the front of the plant and secured and tied with a reef knot, allowing just enough slack to prevent restriction and strangulation.
If the plant is being attached to horizontal or vertical wires or to canes, slipping will be reduced by making a second loop around the wire or cane.
These ties are intended to rot and need replacing from time to time, so regular checks should be made to ensure that the plant is secure and is not being damaged by movement caused by the weather.

© Copyright Brian Davis

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