How to prune shrubs and trees
Ornamental shrubs and trees by no means all require pruning; certainly not regularly. A number profit from it, however, even though they may survive without it. Pruning ornamentals is simply a matter of assisting them to appear at their best.
Whether to prune or not to prune depends to a great extent on the nature, performance and growth characteristics of individual species and specimens. The subject is not difficult to understand.
Pruning before flowering Many shrubs flower during the second half of summer and after. These should be pruned early to allow time enough for the production of the maximum amount of new growth which should bear flowers of the best quality. However, not all shrubs which flower late need pruning—hibiscus, for example.
Among those shrubs that flower in late summer are Buddleia davidii, hypericums, deciduous ceanothus, Spiraea x bumalda, perovskias, Ceratostigma willmottianum, Leycesteria formosa, Hydrangea paniculata grandiflora, hardy fuchsias, and Potentilla fruticosa in its many varietiesThe buddleia, perovskia and cerato stigma should be cut hard back in spring, to encourage as much new growth as possible (in any case, buddleias will become large and ungainly if left alone, even though they will survive). Treat deciduous ceanothus and the taller hypericums in this way, too, if necessary though they do not demand it. Leycesteria may be required to grow very tall; if it is cut back in spring, it will do so. Hydrangea paniculata grandiflora will grow particularly vigorously and flower profusely if cut hard back in spring.
Spiraea x bumalda will soon make a probably undesirable thicket if it is not relieved of some of its older wood and its young growths shortened in March
And, while Potentilla fruticosa rarely requires much attention, March is also the time for any pruning that may be needed. Hardy fuchsias—F. magellanica riccartonii, for example—when cut back in spring, thrust up strong new growth to bear fine flowers in late summer. The old stems, tied together at their tops, as the year wanes, will give some protection to the crowns against winter weather. Left unpruned, fuchsias flower a little sooner, but in time can attain somewhat unmanageable proportions.
Pruning after flowering Early-flowering shrubs on the whole require to be pruned after they have flowered. This allows new flowering wood a chance to arise and mature in readiness for another year's display. It also allows existing unflowered wood scope for full development, so that it may also flower, probably the following year. The point is that many shrubs flower on one-year-old and older wood. Sufficient of this must be promoted and encouraged to ensure regular and worthwhile crops of flowers.
The growths to cut away are, conveniently enough, those that have just flowered. This, basically, makes much of the pruning of this kind of shrub self-explanatory.
Forsythia is a good example of an early-flowering shrub calling for pruning after it has bloomed. If the job is done before the leaves have fully developed, flowered wood is more easily seen and removed and the risk of severing the growths that will flower the following year is reduced. Forsythia is a shrub which is better for minimal pruning, otherwise it may well throw up much non-flowering, leafy growth. Removal of spent growth, only, therefore suits it very well as a general rule.
Kerria japonica flowers on the early side and the flowered growth is best cut away when the blooms have faded. Spiraea arguta and S. thunbergii repay similar attention. Philadelphus, or mock orange, flowers in early summer, so does weigela or diervilla. These shrubs also need pruning after they have finished flowering. They soon make unproductive thickets if the older growths are not cut away. Kept clear of spent wood, they will remain in good form, producing ample new growth which will flower when it ripens.
Syringas (lilacs) require the removal of spent flowerheads when at last the petals have all browned and shrivelled. The buds below the flowerheads should not be damaged; new flowering growth will be produced from these. Thin, twiggy growth, can be cut away at the same time. Brooms (cytisus), too, respond by producing new growth if they have their old shoots with developing seedpods removed. This pruning helps to ensure that there need be little or no cutting back into old wood as the plants mature, because brooms respond poorly to this.
It should also be remembered that there are plenty of shrubs which do not require any pruning at all, even though they flower in the spring and summer period. The viburnums, which flower in spring and summer are examples. The winter-flowering species and hybrids also need little attention.
A number of evergreens flower during the first half of the year. Berberis stenophylla is one, well-known for its sprays of golden-orange flowers and as an excellent hedging shrub. Berberis darwinii, with miniature holly-like leaves, produces its orange flowers in April and May. This, too, makes a good specimen shrub and hedging plant. Both these evergreens may be pruned after they have flowered, though when they are grown as individual specimens, such attention is not essential. Indeed, left unpruned, full pleasure can be taken from their annual crop of handsome dark fruits. When they are used for hedging purposes, however, the need for control does arise.
No pruning needed Mahonia aquifolium and Mahonia japonica are two very showy, early-flowering evergreens which need no pruning at all. Nor does the evergreen Garrya elliptica, whose silver catkins are so handsome during February, although it is better for removal of its dead catkins. If necessary, light trimming is permissible in May. However, those familiar with garrya's excellence for indoor decoration may have trimmed away some of the growth while its catkins were at their best.
Deciduous, winter-flowering shrubs such as daphne, chimonanthus and hamamelis, call for no pruning, though chimonanthus when grown against a wall will. Laterals will require to be shortened after flowering is over.
Evergreen escallonias, flowering in summer, need no regular pruning; any which may become necessary should be done when flowering is over. Evergreen ceanothus, with the exception of those that flower late, come in the same category, particularly when they are grown on walls.
Magnolias, in general, evergreen or deciduous, need no pruning. As far as Hydrangea macrophylla varieties (the mophead hydrangeas) are concerned, congested old wood and spindly shoots should be cut away in spring, though regular pruning is unnecessary. Faded flowerheads should be allowed to remain on the plants during the winter in order to afford some protection to the young growth buds. Cut the dead heads away in spring.
The general run of relatively non‑flowering evergreens, including conifers, grow away very satisfactorily without the need for pruning, but should it become necessary to reduce their height, this should be done in early May. Where such evergreens are used as hedges, light clipping from early to late summer may be done; conifers, however, should be trimmed in early May or August. Rhododendrons need not be pruned unless in time they become straggly. The fairly hard cutting back likely to be necessary under such circumstances should be done in April or May. This will result in the loss of blossom for a season or two, but recovery will follow. If it is practicable the seed pods of rhododendrons should be removed after the flowers have fallen, breaking them away carefully in order not to damage the buds behind them.
Trimming and pinching Lavender, santolina and the evergreen greyish‑ leaved senecios, do not require pruning so much as being kept in good shape. To this end lavender and santolina should have spent flower-stems removed after the flowers have faded and then receive a mere trim over in spring in order to keep them compact. If this is not done, lavenders in particular will straggle, making it difficult to restore the bushes to good condition. Avoid cutting back into old wood.
The removal of awkwardly placed branches in spring, will assist Senecio laxifolius, for example, to maintain a good shape. Mere pinching of soft growth tips during summer is an easy means of eliminating wayward shoots and encouraging bushiness. Hebes respond well to April pruning, should they need to be brought back under control. Pruning at this time is often necessary, in any case, to remove frost-damaged shoots. Summer trimming keeps these shrubs compact.
Heathers (ericas and callunas) will thrive very well, left quite naturally, unpruned. On the other hand, those that flower in summer can be trimmed over in spring; the winter and spring-flowering kinds may be attended to after the flowers have faded. It must be emphasized that such pruning is not essential, even though it tends to improve appearances and may be convenient in individual cases.
Pruning for bark effects A number of shrubs and trees bear particularly brilliant bark if they are encouraged to throw up plenty of new wood. Examples are certain dogwoods such as Comas alba sibirica—vividly red—and willows such as Salix vitellina britzensis—glowing orange. Hard spring pruning is necessary to induce these to produce the maximum amount of young wood with the brightest bark. Rubus giraldianus is one of the showiest of the brambles with `whitewashed' stems. The strongest and most spectacular canes arise from healthy plants which have been cut back annually after flowering.
Wall shrubs and climbers Many shrubs lend themselves to being trained against walls, as well as making good freestanding specimens. Examples include Cotoneaster lactea and pyracanthas, both evergreen, grown for their colorful autumn and winter fruits. Prune these lightly during summer, in order to encourage them to grow as required.
Chaenomeles (cydonia, japonica or flowering quince) is a deciduous shrub which responds well to wall culture. It needs to be spurred back when grown in this way. Cut away laterals after flowering, and then pinch out the tips of resultant young growths during summer. Alternatively, leave the plant unpruned until early autumn, then shorten the lateral shoots well back. Keep forward-pointing growths (breastwood) cut back or pinched back as they develop.
Wisteria is a climber which requires to be spurred back, not only to encour
age flowering, but to curtail the long whippy growths which are characteristic and freely produced at the expense of flowering growth. The end of July is the time when, if practicable, all side growths made during the current year should be reduced to about 15cm (6in) in length. A further shortening to 25cm (1-2in) may take place in November.
Hydrangea petiolaris, an excellent climber for north walls, conveniently requires no pruning at all. The hederas, or ivies, also self-clinging, can strictly speaking, be left alone too. But clipping them over in spring will keep them tidy and encourage the production of fresh young growth. The summer-flowering fragrant white Jasminum officinale, needs no pruning either, though it may be thinned in spring, if necessary. Old, neglected plants may need more drastic treatment. Thin the growths of winter jasmine after flowering, if necessary. Honeysuckle can be left alone, but thin in spring, if necessary, too.
Clematis pruning is straightforward enough if given a little thought and if basic facts about the genus are noted.
The small-flowered species can be left alone, though if the late flowering kinds among them grow too vigorously, hard pruning in February will correct matters. After flowering is the time to attend to the early flowering kinds, should they become a little out of hand.
Splitting the large-flowered varieties into their groups: varieties belonging to the jackmanii and viticella groups require hard cutting back to the lowest pair of healthy buds on each stem, every February, just as the buds begin to show green. Flowers are prolific on their new growth of the current year. Clematis in the florida, lanuginosa and patens groups need no pruning at all to all intents and purposes, after the initial cutting back in February after planting. The may, however, need a little pruning in February, where growth definitely appears dead. And should growth ever become beyond control, then they should be cut back hard in February.
Ornamental trees For all practical purposes, ornamental trees call for no regular pruning at all. Dead, diseased or unwanted wood may arise from time to time, however, and this will have to be removed as with shrubs. Deciduous trees, in the main, should be pruned during the dormant season, avoiding periods of hard frost. But flowering cherries and plums should, wherever possible, receive any necessary pruning after flowering, in order to avoid any problems with gumming and possible infection from silver leaf disease.
Flowering, ornamental trees may at times produce too much growth and leaf at the expense of blossom. This may be due to incorrect feeding, but if the problem is not solved by a change of feed then root-pruning may provide the answer. This involves digging a trench in winter halfway round the tree—about lm (3ft) from the trunk—severing the main roots, and refilling the trench. The circle should be completed the following winter. It is not often necessary to resort to this method in as far as ornamentals are concerned.
Conifers grown as specimens do not need pruning, but any remedial treatment or absolutely necessary cutting back should be done in early May.
General winter pruning This pruning, in general, should aim at keeping shrubs and trees in reasonable shape, keeping branch systems simple and open, and where appropriate, aiming at producing an adequate supply of young healthy wood. During the dormant period, however, most deciduous specimens may need major overhaul, particularly if they have been neglected. Some shrubs are best pruned in winter, when pruning becomes necessary, deciduous berberis, for example. Deciduous cotoneasters can also be brought back under control, where such action is called for, in wintertime, preferably in February.
Pruning principles Cuts should be clean and made back to a joint or growing point, or flush to a main stem, so as to leave no snags and stumps. Failure to do this will almost certainly lead to dead snags. With no developing bud to draw up sap, the wood dries and dies. Shrubs to be cut down should be cut right down.
Before making cuts, particularly those that are a little awkward, it pays to decide sensibly the best direction for saw or secateurs, for example. Snags and stumps are very much more likely to arise where there has been crude and hasty cutting. Neither is necessary. Undercut large branches before making main cuts. They will fall cleanly, without stripping the bark.
Pruning must always be purposeful, directed towards maintaining uncluttered and healthy specimens ; bearing in mind, of course, that some specimens are twiggy by nature. Pruning should not be mere snipping. It should be borne in mind that many shrubs and trees (as indicated above) thrive well enough if they are left entirely alone. Pruning just for the sake of it is a very unsound practice.
You should never attempt to reduce a specimen to a convenient shape, unless it is a hedging plant. Proper balance and natural appearance are paramount. And, while by skilful pruning larger-growing specimens may be kept within bounds in confined spaces, it is nearly always better to have chosen, in the first place, shrubs or trees of suitable proportions.
All pruning is a matter of doing what is obviously best for individual shrubs and trees, according to their natural habit.
Tools for the job Light to medium pruning may be done easily enough with secateurs. There are many different makes. It may be wise to have two pairs, one for lighter work and the other for heavier tasks. It is important to choose a pair which you can use comfortably. There are different styles, sizes and weights, and if work is to be done skilfully and easily, secateurs must fit the hand properly and be used without tedium and strain.
Cuts should always be made in the same plane as the secateur blades. Twisting will result in mangling cuts and straining the tool. Making sloping cuts for the purpose of shedding rain is wise, but cuts must still be made in the same plane as the secateur blades. Cuts should not, of course, be so sloping as to slice wood away from behind a bud or growing point, thus allowing it to dry out.
Secateurs as opposed to shears, should be used for pruning or shaping certain hedges, where practicable. Examples include the larger-foliaged chamaecyparis varieties and the thujas. Cherry laurels and other large-leaved evergreens should be pruned rather than clipped, otherwise the cut leaves will turn brown and die, and look unsightly.
There are several powered trimmers, driven from the electric mains, portable generators, petrol engines, batteries, by flexible drive, and by power take-off units from motor mowers or cultivators.
Loppers, both short-arm and long, are useful. Short-arm loppers or pruners enable tougher cuts to be made with efficiency and speed where it is impracticable to use secateurs. Both anvil-cut
and scissor-action kinds are available. Blades are short and very strong. Long arm loppers, their blades operated by long arms, a form of remote control, enable distant and more inaccessible cuts to be made.
There is a fair range of pruning saws, both single-sided and double-sided. Especially useful is the Grecian pruning saw, short-handled or long. It is curved and pointed and cuts on the back-stroke, making awkward cuts very easy.
Pruning knives were once widely used, but have largely been superseded by secateurs for general pruning. Some craftsmen, however, still use them, particularly in nurseries. They are still useful to have on hand for general purposes, and are still the best instrument for the all-important job of paring smooth the edges of large pruning cuts, especially those made by the saw. They should be used carefully; cuts are best made away from the user.
For the sake of efficiency and safety all pruning tools should be kept in good working order, sharp, clean and well-oiled.
White lead paint, bitumastic paint and proprietary tree-healing compounds should be used for sealing large cuts, to ensure that they heal rapidly.