Pruning Apple and Pear Trees
The principles and practice ofare put to the test with tree fruits more than with flowering shrubs or hedges. The latter need to be restrained and shaped but a few ill-considered cuts – even pruning skipped for a year – will not result in lasting harm. The fruit tree is less amenable to the casual approach. To persuade it to produce regular crops from an early age it must be ‘built’ into a fruit production unit -often of unnatural shape – and every piece of growth must be assessed for its ability to increase fruiting potential.
The year after budding or grafting, the scion bud sends up a ‘wand’ of growth, and this first-year tree is known as a ‘maiden’. These can be purchased by the gardener who wishes to carry out the critical first phase of training which is to secure the basic framework of branches. Alternatively this is done by the nurseryman, and the gardener buys a two- or three-year-old tree at a correspondingly increased price.
The continuing aim of fruit-tree pruning – especially of apples and pears – is to keep the tree balanced in shape, and balanced in the proportions of old and young wood. ‘Cutting back’ is too simple a definition of pruning to apply to tree fruits. Such an arbitrary approach will only serve to delay and reduce the yield of fruit. An unpruned tree, if it is on dwarfing stock, will fruit early in its life and keep bearing. But – and this is why we prune – it will soon become crowded with growths, unhealthy, and bear small (if numerous) fruits irregularly.
So the gardener seeks a compromise by building a tree of manageable shape in the early years, and thereafter by selective pruning maintaining the same proportions while it grows bigger.
An important qualification is that different varieties have different natural growth habits which lend themselves to one form of training and pruning rather than another once the framework is established.
Winter pruning of apples and pears can be tackled after leaf fall and is better done early in the winter than late. Similarly a young tree is best planted and cut back in early winter. Summer pruning, which helps to control vigour and exposes ripening fruit to sunlight, is carried out in the height of the season.
We have seen that a tree may be purchased as a ‘maiden’ or as a two or three-year-old. The maiden comes as a single ‘wand’ of growth which must be cut back after planting. A bush tree is the only-sensible shape for the modern garden and this means cutting back to leave a stem of about 75 cm (2 ft 6 in), using a sharp pocket knife, or equally sharp secateurs.
From below this cut in the following spring the growth buds will extend as shoots, the strongest just below the cut, the others in descending order of vigour. The top three shoots are retained as prospective branches of the tree. Ideally, these branches should emerge at a wide angle from the stem, but it so happens that the topmost bud always emerges at a narrow angle and grows up almost vertically. However, the next bud down makes a better angle, so a way has been devised of rejecting the unsuitable top bud. Before the buds break, a small piece of wood is nicked out just below the top bud. So, diverting most of the sap energy to buds below. The following winter the stub above the new top shoot is cleanly cut away. If any of the three top buds is close to its neighbour, it is best cut out and allow another lower one the space to grow.
We have reached the stage at which three shoots – framework branches – have been secured, either in the nursery before purchase or by the gardener. In the winter following their extension each of the three is cut back about two-thirds. If possible choose a point above an outward-facing bud and always cut at a slight slope away from the bud.
From below this cut at least two shoots can be expected to extend from each parent branch. So the following winter there are six more branches (six is a good number), which this time are cut back by half their length. One more year’s development gives an ‘adult’ tree with an optimum of twelve branches spaced evenly all round with none growing into the centre.
THE AIM OF SUBSEQUENT PRUNING
After this, hard pruning ceases and attention is directed towards keeping a balance between old and young wood. It is important to recognise by looking at the winter buds whether they will make growth shoots orand fruit. Growth buds are slim and pressed tightly to the stem, while fruit buds are fatter and stand more away from the stem.
Look at a branch in winter that has been growing (and been pruned) for three years. The top section will be bearing mainly growth buds, the middle section mainly fruit buds, and the oldest section will have groups of fruit buds called spurs. With the renewal pruning method to be described shortly this type of branch is kept for several years until replaced by a younger cropping unit. As well as vigorous and potentially useful laterals from the main branches, short and weak growths will also appear. Invariably these should be pruned hard back -by at least two-thirds – for they have no future as replacement branches. It is a safe rule of thumb to prune weak growth hard, and strong growth lightly once the tree framework has been formed. Any attempt to control vigorous growth by hard pruning will be met by an even more vigorous response by the tree. On the other hand there is a chance that stronger growth will result from the hard cutting-back of a weak shoot.
The following section deals specifically with apple-tree pruning. Just as a number of trained tree shapes have become accepted as distinct forms (bush, dwarf pyramid, cordon etc), so a number of pruning methods have been developed to deal with certain training systems or with certain varieties. Essentially these can be narrowed down to two: established spur pruning and renewal pruning. The latter is the more natural approach with a bush tree. However, variety has an influence on choice, and the firm favourite Cox’s Orange Pippin has growth that lends itself to spur pruning.
RENEWAL PRUNING OF APPLE TREES
Renewal pruning suits most bush apple trees. In its simplest form the method involves the winter pruning of some new growth and shoots that have carried fruit. Leading lateral branches are left unpruned in order to develop fruit buds along their length. When they are brought down near the ground by the weight of fruit it is time to replace them. For this purpose a sub-lateral, upward growing and suitably positioned, has been kept lightly pruned. The old branch is cut cleanly away at its junction with the replacement leader.
Shoots are not pruned until after they have borne fruit, but once this has occurred (on two-year-old wood) the shoot is ready to be renewed. This is done by cutting it back to within two buds of the main branch. Renewal of fruiting wood is the aim of the system. Young shoots arising directly (that is, not associated with wood that has borne fruit) are nearly all left unpruned in order to make fruiting wood the following year. But a minority are cut hard back to two buds. Temper this cutting back according to tree vigour. If the tree is vigorous leave a number of these shoots unpruned each year. Hard pruning of nearly all new shoots is the rule on weaker-growing trees.
This ‘staggering’ of shoot pruning helps to overcome the tendency known as biennial bearing – heavy crop one year, none the next.
ESTABLISHED SPUR PRUNING
In contrast to the renewal method, fruit-bearing wood is left to develop a fruiting spur system with established spur pruning, instead of being replaced after fruiting. Each new shoot is cut back according to its vigour: to four or five buds if vigorous, to one or two if weak. In future years growth shoots from this spur are treated similarly, with the result that a group of spurs consisting almost entirely of fruit buds is built up. Clearly some shoots must be treated differently, and the leading shoots on branches are only lightly pruned by the removal of the top inch or two. And a minority of shoots of medium vigour are not spurred back until they have fruited.
Vary the number of spurred and unpruned shoots according to tree vigour, spurring weak growth and sparing the strongest. Spur systems get crowded after a few years and themselves need pruning. Thin out up to half of the clusters to allow space for fruit development and light for ripening.
Summer pruning is carried out about a month before a variety is picked — usually from mid to late summer – and at such a time there should be little if any regrowth from the cut shoots. Its result is to expose fruit and wood to the beneficial effect of light and air: it can reduce pest or disease incidence and will give a “check” to vigour. Weakly growing trees should not be summer pruned. So shorten new shoots to 8 cm (3 in), wherever this will expose ripening fruit.
REJUVENATING AN OLD TREE
Old apple and pear trees are often found in a neglected state, and fit at first sight only for grubbing out. However, with remedial pruning over a period of years such trees can be given a new lease of life. Neglect and abuse may have resulted in one of two ways. Where no pruning has taken place for years the tree will be overgrown with worn-out fruiting spur systems. The other possibility is that the tree has been ‘hacked’ instead of pruned so that it is a mass of congested shoots and quite fruitless.
In the first case, a procedure known as de-horning is adopted. This is drastic pruning and involves cutting out one or two branches each year as close to the crotch of the tree as need be. Initially remove branches that crowd the centre, and later thin out the periphery if necessary. Aim to reduce overall height by cutting to a point where a lower branch can take over. Cut cleanly at these junctions, making sure that the wound is properly sealed. If there are not many branches to be removed but spur clusters are crowded on old wood, thin out these clusters by half over a period of some four winters.
A tree that has been hacked to resemble a pollarded willow again needs whole branches cut out before shoot thinning is tackled on the remainder. The aim should be to encourage a new framework of well-placed branches by selecting some of the best-placed shoots to be new leaders and tipping them. Leave enough of the others as laterals which will make fruit buds if left unpruned. Cut out at their base very lengthy, vigorous vertical-growing ‘watershoots’ from old wood.
Fruit spurs form more easily and abundantly on pears than on apples, so that they are well suited to be trained in shapes such as cordon or espalier and pruned by the established spur system. Bush trees can also be formed without any trouble, along the lines described for apples. With pears it is generally easier to achieve the ideal ‘goblet’ shape with an open centre.
To form a low-growing bush from a maiden tree, allow three well-spaced shoots to develop after cutting back, then double the number by pruning each to two buds. Treat further growth on established-spur-principles described below.
Summer pruning is of more benefit to pears than apples, and is most important on trees trained to special shapes. The method is to reduce weaker side shoots to four leaves and stronger ones to six leaves. This is followed up by winter spur pruning back to two buds. As with apples, a minority of shoots can be left unpruned for a year to ensure a succession of fruit buds.
Leaders need to be cut back by a third in winter (with most apple varieties they are just tipped). Thick spur clusters soon develop on pears and need to be thinned progressively.
SPECIAL TREE SHAPES
By definition these trees are dwarf and pyramidal in shape. Dwarfness comes from the rootstock, and the best ones for this form of tree will be recommended by the nursery. In contrast to an open-centred bush tree, the central leader must be retained to serve as the ‘spinal column’ of the pyramid. If a maiden is planted and then cut back in the normal way, the top buds must be stimulated into strong growth. The top one will be vigorous enough, but the next three or four can be encouraged by nicking out a small piece of bark above each one.
In the early winter of the following year these shoots are pruned back by half, cutting to a bud on the underside so that the shoots tend to grow out at a wide angle. Continue to winter prune the central leader so that it maintains vigorous vertical growth and keep the extension growth of the other main branches in proportion so that the shape continues to resemble a Christmas tree. As the leaders extend, tiers of side shoots will develop. Once the lowest side shoots have borne fruit all side shoots are summer pruned and spurred back in winter as described earlier for apples and pears. A pattern develops of tiers of laterals with sub-laterals.
Once the central leader has reached the maximum height desired, the relatively hard winter pruning of leaders ceases.
As with other restricted tree forms, trees to be grown as cordons should be on a dwarfing rootstock and of an amenable variety. Ask your nurseryman for suitable varieties. The various cordon shapes and espalier trees require a supporting framework of posts and wire, which is best set up before the row is planted. Wires can also be fixed directly to a garden wall. There is little point in choosing a space-saving tree form unless several are planted, and this makes economical use of the posts and wire. These must be stout and durable, and wood posts -though the best looking – will need replacing one day. Angle-iron or old piping is probably the best and needs to be sunk deeply or buried in concrete. Concrete posts will also serve, though they tend to be bulky. Use strong wire and intermediate supports every 90 cm (3 ft) or so. Wires at 60, 90, 120 and 150 cm (2, 3, 4, and 5 ft) from the ground provide a good supporting system.
Best known of the variations on the cordon theme is the oblique cordon, and this is considered the best for the average garden. More space is required by the single U-cordon, which itself can be compounded into a double U-cordon.
The oblique cordon begins life as a single stem and remains thus throughout its cropping life. To form such a cordon of your own, start with a maiden tree and plant it close to the wire at an angle of 45° to the ground. Allow 90 cm (3 ft) between each tree and plant so that the graft union (visible as a swelling just above themark on the stem) faces the ground. This is done because the base of the tree will be under pressure and the union might split if facing upwards. With each cordon a bamboo cane is required, tied to the wire at a 45° angle, to which the maiden tree is secured with soft string.
The leading growth is allowed to extend each year, and cane and cordon are lowered by about 5° when the top wire is reached. This procedure reduces vigour and leads to plentiful fruit-bud formation. Summer pruning is the main treatment for a cordon. It begins the summer after planting when shoots are shortened back to four or five leaves in mid-summer. In winter they are spurred back further. Thus spur systems develop on the lowest part of the stem and extend upwards each year. By the time most of the cordon is clothed with fruit spurs it is time to practise spur thinning on the oldest.
As always, use discretion in pruning according to tree vigour, cutting back thin weak shoots harder than average and very strong ones less hard. This is a simple and rewarding way to grow apples or pears in a small garden.
To make a single U-cordon, the maiden tree is cut back to about 30 cm (1 ft) and two resulting shoots are allowed to extend in opposite directions, then tied to canes on a wire 30 cm (1 ft) above ground. After about 15 cm (6 in) of growth has been tied to the canes the shoots are turned upwards and tied to upright canes. In winter they are pruned by about one-third. In successive winters they are just tipped, while all side shoots are summer and winter pruned to make spurs. Skill is exercised in keeping both arms of the U at the same height, and there is twice the work in the double U-cordon.
This horizontally spreading shape requires around 4.5 m (15 ft) of wall or post-and-wire space per tree. The system is built up in tiers, tapering to the top. A maiden is cut back to about 45 cm (18 in), to a bud above a pair lying opposite each other. The terminal bud and the two below are allowed to grow, the terminal being tied to a vertical cane on the wire-supporting framework, the two opposite shoots to canes at an angle of about 45° from the leader in order not to weaken them by making them horizontal at once. They are lowered to the bottom wire at the end of the first growing season, but if one is weaker it is only partially lowered. The vertical leader is winter pruned back to about 60 cm (2 ft).
During the next growing season, two more suitably placed opposite shoots on the vertical leader are chosen as the second tier of the espalier, and other shoots in the same region are pinched hard back while young. In this and future years all side shoots from the tiered branches are summer pruned according to vigour, and spurred back in winter.
The formation of each tier follows the same pattern as the first; namely, supporting the opposing shoots first at 45° then lowering them to the horizontal while keeping a balance for vigour.