Training and Pruning Plants, Trees and Shrubs
Although many gardeners imagine that pruning is performed only on trees and shrubs, any removal of shoots, branches, flowers or other parts from a growing plant amounts to pruning, and many of the same underlying principles apply. In this part of the site, I have followed convention, however, and these accounts relate only to the pruning of woody plants.
Continually pruning a young plant will dictate its overall shape as it matures. This operation is called training, and the process by which it is done is generally known as formative pruning. The choice of training method can have a considerable bearing on the plant’s productivity, and cordon or fan-trained fruit trees grown against walls are good examples of this. The need to train a plant into a chosen shape is, therefore, the first of the reasons for pruning. The routine pruning performed on it thereafter is usually called maintenance pruning, and this is done mainly to increase the production of leafy shoots (part of the reason for pruning or clipping hedges), or of flowers and fruits (the usual reason with ornamental and fruit plants). A further reason is to encourage overall vigour by removing overcrowded shoots and branches and letting light and air penetrate. Finally, pruning can actually improve the health of a plant when it involves removing either diseased parts, or any redundant or moribund tissues (like dead flowers) that are likely to provide disease-causing organisms with a foothold.
Using pruning to shape a plant makes use of the tact that taking off the end of a shoot, with its associated buds, stimulates those buds lower down to burst into life. This is why regular clipping of a hedge will thicken its overall growth. This important principle of pruning and training is based on disrupting a phenomenon called apical dominance, in which the growing buds at, and close to, the tip or apex of a shoot produce chemicals that inhibit the growth of those below them. Sometimes, simply bending the leading shoot from a vertical position towards the horizontal is enough to reduce apical dominance and stimulate flowering lower down.
Tools for pruning for most pruning tasks, a pair of secateurs (sometimes called primers) will be adequate although for thicker, tougher stems, loppers and a pruning saw are necessary. Hedge-clipping is achieved either with hand shears or powered trimmers.
How to prune
In order to follow pruning instructions you need to identity the main stem (known as the leader), the laterals (the side-shoots that arise from the main stem) and the sub-laterals (side-shoots that arise in turn from the laterals). When pruning fruit and blossom trees you may also need to recognise a spur, which is a short, stubby shoot on which flowers and fruit develop.
Always make pruning cuts immediately above a bud, leaf, flower, branch division or other actively growing structure; never in the middle of a length of shoot. This ensures that natural healing of the cut surface takes place swiftly. Always position the cut approximately 6mm (1/4in) above the bud or other growing part and sloping away from it. To control the direction of future growth, look at the way the buds lace. By cutting above outward-facing buds you will encourage shoots to grow out-wards, leaving a more open centre to the plant. By cutting above an upward-facing bud, you will encourage shoots to grow upwards, giving a narrower, more upright habit overall, but with a much greater likelihood of shoot congestion. Take special care when removing large branches from trees, especially from the main trunk. Never allow the saw cut to damage the swollen base or collar of the branch, for within this zone are the tissues that promote healing; and never apply wound-sealing compounds to the cut surfaces of pruning cuts.
When to prune
Flowering and/or fruiting shrubs, trees andfall into two groups: those that flower early in the year on wood produced during the previous season and those that flower after midsummer on wood produced during the current year. In order not to remove flower buds, pruning is performed after flowering. Those shrubs that flower on the older wood are pruned as soon as the flowers fade, and this usually involves little more than a general tidying up and removal of dead flowerheads. Plants that flower on the current season’s wood may be pruned at any time between late autumn and early spring, but the advantage of leaving the work until spring is that the old growth provides some protection overwinter.
The timing of pruning foris less critical but their ability to withstand hosts and cold winds needs to be taken into account. Any plant of borderline hardiness (and also many evergreens) are best pruned in the spring, although long growths that could be blown about and damaged in the wind may be removed in autumn.
There may be other factors to consider with particular species. Vigorous plants, such asand many hedges may need pruning twice a year, while trees such as willows and walnuts have a strong sap flow in spring and early summer so pruning cuts made at this time can weep badly and weaken the plant. Plums and related plants are prone to silver-leaf disease and as the spores of the causal fungus are produced in autumn and winter, pruning must be done in spring or summer.
How severely to prune
I mentioned earlier that the removal of apical buds stimulates others (usually called lateral or side-buds) to grow. Essentially therefore, the more of the main shoot that is removed, the greater will be the stimulation of the side shoots. And the greater the severity with which these, in turn, are cut back, the greater is the proliferation of shoots overall. The practical consequence is that severe (or, as it is usually called, hard) pruning should be used in order to encourage more growth from a plant that is growing feebly or is inherently weak. Conversely, a very strongly growing plant should, in general, be pruned lightly in order to contain its vigour.
Basic Pruning Methods
Annual renewal pruning
This is a very important pruning technique for plants that flower after midsummer. Either the whole plant is cut back to just above ground level in early spring, as with Buddlieja davidii, autumn-fruiting raspberries and some dogwoods (), or, and much more generally, only a proportion (usually the oldest one-third) of the stems is removed each season. The remaining stems are left unpruned or are lightly pruned (to less than half their length) and so the plant is entirely renewed every three years.
Light pruning or trimming after flowering
This is the most common pruning technique for those plants that flower before or shortly after midsummer. It is a more extensive version of dead-heading; the dead flowerheads are cut back well beyond the base of the flowers and some re-shaping of the plant is done at the same time. Hand shears may be used to trim lightly over bushy plants as the flowers fade; trim to below the base of the dead flowerheads but not more than a few centimetres into the older wood.
Overgrown and neglected trees and shrubs can often be rejuvenated by pruning and removing dead and diseased parts, overgrown and crossing branches and weak shoots. This stimulates new young growth although it is best to spread the task over three years, doing one-third of the pruning each year. Much of the benefit results from improved penetration of light and air to the centre of the plant.
Pruning for damage and disease control
If a part of a plant has simply been damaged (a branch broken by a gale, for instance), that damage won’t itself spread and it might be thought that no treatment is needed. Complications arise, however, if the broken tissues are then invaded by a disease-causing fungus, but the likelihood of this arising can be minimised if the wound is ‘cleaned up’ promptly. Branch stubs should be cut off, neatly, broken branches cut back to the basal collar and any damaged tissues cut back carefully to healthy wood or bark.
Understanding disease biology will also help to indicate the value of pruning as a control. For example, during the winter the rose black spot fungus survives in small lesions on the shoots. Hard pruning in the spring to remove these diseased shoots is of much greater value, therefore, than collecting diseased leaves. It is important, also, to recognise the difference between localised diseases and much more deep-seated or widespread problems. Most fungal cankers (like apple canker) are classic-examples of localised problems: there isn’t much infection beyond what can be seen, so if a branch bearing a canker is cut away neatly, there should be no further spread. Bacterial cankers (like those on plums and cherries) are often associated with extensive contamination of the tree, however, and so cutting out an individual lesion may have little overall effect.
Training and pruning notes for the main groups of garden plants
No training is needed with free-standing shrubs, although standards will need staking like young trees, but shrubs can be trained against a wall to form a more-or-less two-dimensional structure, simply by cutting away any shoots that point directly towards or away from the wall and then tying the main branches to the wall. Spur-pruning will also be necessary on many flowering wall shrubs: the side-shoots arising from the main framework should be cut back to within about 10cm (4in) of their bases each year to produce short flowering shoots or spurs.
Be guided especially by flowering time and always prune after flowering is complete. Remember that deadheading will generally encourage repeat flowering, either immediately or later in the season: cut back the dead flowerhead to just above the first leaf with a plump bud in its apex. Many flowering shrubs also benefit from three-year renewal pruning.
Most foliage shrubs perform reasonably well without special attention, but many will benefit from three year renewal pruning. Timing is less critical than for flowering plants, but spring is the best pruning time overall.
Training and support
Newly-planted trees are usually top heavy and likely to be rocked by the wind, so support in the form of a tree slake will help their roots to establish more quickly. A typical tree stake is 5cm (2in) in diameter with 2m (6-1/2ft) above ground and 75cm (2-1/2ft) below; these stakes are still very popular, although more recent research has shown that shorter ones, with only 75cm (2-1/2ft) above ground allow the tree to flex and so develop greater wind tolerance. Stakes are best positioned at planting time when there will be less damage to the roots. Place the stake on the side of the stem facing the prevailing wind so the tree is blown away from, not on to it, and secure it with an adjustable tree tie with a buffer between the bark and the stake.
When tree branches overhang buildings or other types of obstacle and for the wholesale reduction in size of trees that have grown too large for their site I urge gardeners to use a tree surgeon, preferably affiliated to a recognised professional body. Not only do tree surgeons have the necessary practical experience, but they will also have insurance protection in the event of any mishaps. The complete removal of unwanted trees is also generally a matter for a professional. Apart from the difficulty and danger of felling the tree itself, the stump must be dug up, ground down or winched out, the latter two requiring expensive equipment.
Suckers are produced by trees and shrubs where the chosen variety has been grafted on to a different rootstock. Suckers should always be removed, for they will invariably draw nutrient away from the grafted variety, but they should be pulled, not cut away, if the result isn’t merely to be the stimulation of yet more suckers.
Remember that care in choosing varieties of trees and shrubs and simple routine attention (such as rubbing off buds or leaf clusters that arise on the bark of standard specimens) will very often obviate the necessity for any remedial pruning later.
All of the above relates to the pruning of the above ground parts of trees and shrubs but there will be a few occasions when root pruning is desirable. Usually the need only arises when a plant has been chosen inappropriately for a site and, for various reasons, it is undesirable completely to remove and replace it. Root pruning is most commonly used with apples, pears or a few types of ornamental trees but should never be done on plums or other Prunus species, willows or poplars as they will respond by excessive production of suckers. Root pruning is achieved by carefully digging a circular trench in autumn approximately 45cm (18in) deep and at a radius from the trunk determined by allowing about 12cm (5in) for every 1cm (1/2in) of trunk diameter. The fine roots should be left intact and the thickest roots severed. After the operation is complete and the trench refilled, the plant will almost certainly require the added support of a slake.
Training and pruning
Training is usually only required with climbing and rambling roses, which may be treated in the same way as other(below ). Large shrub roses will benefit from tripod or similar stout supports. Most types of rose, however, do require rather careful pruning and, for the best results, you should use one of eight techniques appropriate to the various rose groups. The task is best done in the spring and the only autumn pruning I do is to remove long whippy shoots to prevent the plants being rocked by winter winds. Rambler roses are the only group to require summer pruning although, of course, deadheading should be done throughout summer to prolong flowering.
Although a few common climbers like ivy and Boston ivy (tricuspidata) are self-clinging and therefore require no additional support, most climbers need tying and training. Twining climbers, like wisteria, grasp supports by wrapping their entire stems around them and growing upwards. These are most successful, therefore, where the principal supports are vertical.
Climbers such as clematis and grape vines have tendrils which are much more effectively supported by horizontal wires. Trellises, if strong enough, having both vertical and horizontal elements, are useful for both twiners and tendril climbers.
Climbing roses are grapplers that rely on backward-facing spines, a rather crude system, and although to some extent they may be twisted around vertical supports (as with pillar roses) they also need to be tied securely to their supports to prevent them from becoming tangled.
Walls offer the best support for climbers and all except self-clinging types need horizontal wires fixed 20-25cm (8-10in) apart. Use 2mm diameter, plastic-coated wire that can be tensioned without snapping and attach it to looped vine eyes, screwed into wall plugs. For large climbers, stronger wires with straining bolts may be needed, although very heavy plants like established wisterias are best secured with individual vine eves.
Trellis can be an attractive feature in its own right but its strength depends on the thickness of wood and method of construction, so be sure to choose a type appropriate to your plant. It may be made free-standing but if it is being attached to a wall, fix it first to 2.5cm (1 in) battens so that air can circulate behind it. Trellis may also be used as a top to increase the height of fences or walls, as screening and as an in-filling in arches and other structures.
There are many free-standing supports like archways, pergolas, pillars and tripods that provide an opportunity for training climbers. But choose a climber with vigour appropriate to the size of support; many arches and obelisks are only strong enough for the less rampant types. Train the stems so they are almost horizontal to encourage flowering all along their length.
The same basic pruning principles relating flowering time to pruning apply to climbers as well as shrubs, and if climbers are thought of as long thin shrubs, their pruning will seem much more logical. Clematis, which many gardeners find confusing, illustrate this well. They can be divided into three main groups for pruning purposes, depending on when they flower:
Clematis that flower early in the year on wood produced the previous season. Prune immediately after flowering by cutting back all weak and dead stems to just above a bud.
Clematis that flower on wood from the previous season but in early summer, rather later than the Group 1 types. Prune in early spring by cutting out any dead or weak stems and cut back remaining shoots by about 30cm (12in), cutting to just above a pair of plump buds.
Clematis that flower later in the summer on the current year’s wood. Prune hard in early spring to remove the previous season’s growth, cutting back to just above a pair of plump buds about 75cm (30in) abovelevel.
Training and pruning
To reach their full potential, fruit trees must be trained and pruned from a young age and I have subdivided the descriptions here according to fruit type, as each requires rather different treatment.
Apples and pears
The easiest way to grow apples or pears is as a freestanding bush. No support is necessary other than a tree stake and only winter pruning is required. It is simplest to start with a one-year-old tree (called a maiden). During the first winter after planting, cut back the single shoot to a healthy bud at about 60-90cm (2-3ft) above soil level. This will result in several upright shoots being produced over the next year.
The second winter, cut out the middle shoot to give the tree an open centre. The four strongest shoots remaining should be cut back by about half their length. Remember, always cut to an outward-facing bud to maintain the open centre. Remove any other long shoots and also cut back laterals to about three buds.
In the third and subsequent winters, maintenance pruning takes over from formative pruning and the trees should be pruned in winter by cutting back the side-shoots on each branch to two or three buds above the base and shortening the leading shoots on each branch by up to one-half. The less you need to cut back established trees, the better.
Growing apples or pears as cordons can save space but requires summer as well as winter pruning. Set up a system of horizontal wires between firmly braced posts, spacing the wires 60cm (2ft) apart to a height of 2m (6-1/4ft). Plant a maiden tree with a supporting cane at an angle of 45 degrees and tie both tree and cane to the support wires. Prune all side-shoots longer than 10cm (4in) to a point just above the third bud from their bases. Thereafter, every year in late summer, cut side-shoots longer than 20-25cm (8-10in), and growing directly from the main stem, at a point just above the third leaf above the basal cluster. At the same time, cut shoots arising from the side-shoots at a point just above the first leaf beyond the basal cluster. Prune established cordons in late summer by cutting back all the side-shoots longer than 20cm (8in) to a point three leaves above the base. Also cut back any small shoots arising from the side-shoots to one leaf above the basal cluster. Once the leading shoot has reached its allotted length. Treat it in exactly the same way as the side-shoots.
Pears especially are very successful when grown as espaliers. An espalier consists of a central stem bearing tiers of paired horizontal branches, trained flat against a wall or support wires. After planting an unfeathered maiden in winter, cut it back to about 40cm (16in) above soil level, just above three plump buds. The top-most of these buds will grow to become the central stem, and the two below will develop as the two lowest branches.
In summer, tie the top shoot in to a vertical cane, and the two lower ones to canes placed at angles of 45 degrees. Then, in late autumn, carefully lower the two branches so they are horizontal, and tie them into support wires. If one is weak, cut it back by about a third to an upward-racing bud. Otherwise, do not prune. At the same time, in order to create the next tier, prune back the central stem to about 45cm (1-1/2ft) above the lower branches, again just above three strong buds. Cut back any other shoots to three buds. In the following summers, as before, tie in the side branches at first at an angle of 45 degrees, and then in late autumn lower them to the horizontal. Continue this system of summer and autumn pruning until the required number of tiers has been formed, at which point the central leader should be cut back in summer to check further growth. The arms of the espalier are then maintained in a similar way to a cordon in order to encourage fruiting.
Plums, cherries, peaches and apricots
A maiden plum tree is best planted in late autumn, but should not be pruned until bud-break in early spring. Then cut back the leader to just above four or five plump buds at the required height, allowing for a stem of about 90cm (3ft) for a bush and 1.4m for a half-standard. Any laterals should be cut back to about 7.5cm (3in). They will eventually be removed but for the time being help to strengthen the main stem.
The following summer, pinch back any new growth on the laterals, leaving no more than four or five leaves. By early spring of the second year, several strong new shoots will have developed. Choose four that are well-spaced and wide-angled to form permanent branches. Cut each back by one-half to two-thirds to an outward-facing bud. Remove all laterals.
In the spring of the third year choose up to eight strong outward-growing secondary branches to form a balanced framework. Cut the new growth on all of these back by between one-half and two-thirds, always cutting to just above outward-facing buds. At the same time, prune back laterals on the inside of the tree to about 10cm (4in), but leave laterals on the outside unpruned. Thereafter, pruning should be kept to an absolute minimum and the tree allowed to settle down to crop.
To train a fan, early in the first summer after planting a well leathered maiden (a young, untrained tree with several side-branches), cut out the main shoot at a point just above a pair of strong side-branches about 30cm (12in) above soil level. Tie these ‘arms’ on to diagonal canes attached to the main support wires. The following spring, cut back the two arms to points above a bud about 30cm (12in) from the main stem. Cut back shoots arising from the arms to three or four buds from their bases. The following spring, further shoots will have elongated from the arms. Two should be selected above and two below each of the initial shoots, tied in and shortened as before. Other shoots should be cut back to their bases. On a large wall, more arms can be created the following year, but stop once the allotted space is covered. Thereafter, annual maintenance pruning is required in spring. First cut out any shoots growing directly towards or away from the wall then, on each blossom-bearing side shoot, pinch out some of the leafy buds to leave one at the tip. One at the base and one in the middle. In early summer, pinch back each side-shoot to a point just above six leaves from the base. In late summer, cut back each fruited side-shoot to its junction with the new side-shoot and then tie in this new shoot.
Figs are best grown as fans, trained initially as for plums. Thereafter, the pruning is dictated by the fact that, in cool climates, the fruit won’t reach harvesting size within one season. The most important fruits are the pea-sized ones that appear in late summer at the tips of young shoots. If they survive the winter they should ripen by late summer or early autumn the following year. A second crop develops on new shoots in spring but fails to ripen, and should be removed in late autumn.
In early summer, pinch back to about five leaves from the base all of the young shoots growing out of the ribs of the fan. These shoots will harden and produce embryo fruits in late summer. In midsummer, some old and unfruitful wood may be thinned out to let in more sunlight to ripen the fruit.
I find it best to do the majority of the pruning in spring, leaving on the old wood to give protection in winter. So, in spring, cut back to 2.5cm (1in) about half of the shoots that have borne fruit, in order to encourage new growth. The shoots that remain should be about 25-30cm (10-12in) apart, and should be tied in. Any other unwanted shoots should be removed completely and you should remove any shoots growing directly towards or away from the wall.
Soft Fruit Training
The woody soft fruits are divided loosely into cane fruits (raspberries, blackberries and their relatives), bush fruit (gooseberries and currants) and the climbing grapevines and kiwi Fruit. The bush fruits need no support but training is necessary. Cut out some shoots at an early stage to prevent overcrowding, the aim being to create a goblet-shaped plant with a fairly hollow central structure.
The best support for cane fruits is a system of horizontal wires between braced vertical posts. I use round, rustic, tannalised wooden posts, 3.5m (1-1/4ft) apart and sunk 45-60cm (18in-2ft) into the soil leaving a height of 1.8m (5ft 9in) above. Use plastic-coated 10-gauge or 3mm (1/16in) diameter wire. It can be twisted two or three times around each post or attached to bolts screwed through each post then pulled taut by hand. The wires are most usefully positioned at 60cm (2ft) above soil level. Individual canes should be tied to the wires with soft, degradable string in a figure-of-eight pattern.
The simplest training method is the Scottish stool system where the canes are allowed to emerge as a group from each stool and tied in a fan-pattern to the wires, any excess canes being cut out.
Blackberries and their hybrids have long flexible canes and, to cope with them. I favour the fan-training system which gives the highest yield although it is rather time-consuming. It is best employed on the single bay system where the new canes that will bear next season’s fruit are tied up through the centre and then out along either side and over the top of the old canes that bear the current year’s crop.
The canes of summer-fruiting raspberries, blackberries and all the hybrid berries should be pruned to soil level once the fruit has been picked, and the new canes then tied in. Cut or pull any canes emerging too far from the support wires and limit the number of new canes to eight or nine per metre (yard). Autumn-fruiting raspberry canes must be left until late winter and then pruned to soil level.
After planting, cut back all shoots to just above two buds from the base. At the end of the first fruiting season, when the number of branches on the new plant should have at least doubled, cut back one or two to just above two buds from the base, and also cut out any weak shoots, cutting back to their junction with the parent branch.
In the second year, and in each subsequent year, cut back the oldest one-quarter or one-third of the shoots to just above the base, as well as any that are hanging very close to the ground. Also cut out any weak or damaged shoots. This may be done at any time between the ripening of the fruit and midwinter; some gardeners choose to do it when they are harvesting the crop.
Red and White Currants and Gooseberries
Training and pruning
All three fruits are grown most conveniently as free-standing bushes, or as cordons against horizontal wires. Bach method entails different training but essentially similar pruning.
With a bush, the aim is to produce a goblet-shaped plant with an open centre. In the first winter after planting, cut out any branches at the centre of the bush, and cut back the remaining branches by about one-third, to just above a bud. In the following winter, repeat the cutting back process; by now there should be eight to ten branches, which is the maximum number required. About six weeks after midsummer in every subsequent year, cut back the leading shoots of each branch by about one-third, and any side-shoots on them to just above six leaf-clusters from their base. And every winter, cut back the leading shoots of each branch again by a third, and all side-shoots to two buds from their base. Also remove any branches that grow up from the middle of the plant, and any suckers from below soil level. Occasionally you may need to train a new branch to replace one that is damaged.
Think of a cordon as one, two or three branches (single, double or triple cordons) trained vertically against a support; and remember that the pruning is essentially similar to that of a branch growing normally on a bush. In winter, after planting, select the strongest vertical branch(es) to tie in to the support wires, and cut out the remainder. About six weeks after midsummer in the following year, cut back all side-shoots to just above the sixth leaf-cluster from their bases, but leave the leading shoot untouched. In winter cut the side-shoots back again, to two buds from the base, and cut the leader back by approximately one-third. Continue this process until the leader reaches the top of the wires; from then on treat it in the same way as the side-shoots.
Grapevines / Kiwi Fruits
Training and pruning
Immediately after planting in early winter, cut the main stem down to about 60-75cm (2 – 2-1/2ft) above soil level, cutting to just above a bud. Support the stem, or ‘rod’, by tying it to a vertical cane. During the first summer, allow it to grow up to the topmost wire, and then pinch out its top. The strongest of the side-shoots should be tied in to the wires on either side of the rod, and pinched out just beyond five leaves from their base. Any other existing side-shoots should be pinched out altogether. In the following winter, cut back the rod by about half, and cut back the side-shoots to about 2-5cm (1-2in) from their bases. During the second summer new side-shoots will grow out from these stubs: only one strong one should be allowed to develop and tied in to the support wires; weaker ones should be pinched out. In winter two years after planting, again cut back the rod. Which will gradually be approaching the top of the wall, and cut back the side-shoots to leave 2-5cm (1-2in) stubs.
Pinch out the laterals in summer at three leaves beyond the first flower-cluster in the first year, the second in the second year, and the third thereafter. Every winter the side-shoots should be cut back to leave short stubs; and when the rod has reached the top of the wires it should be treated like a side-shoot and cut back to the same point each year. Always remember that grapevines and kiwi fruits are big vigorous plants and if you are negligent in their pruning they will very soon become an unruly, unfruitful tangle.