Organic Gardening Tips and Methods Ornamental Trees (Part 8, Section 1) Pruning and Training Correct pruning and training helps to maintain a trees health and vigour, regulate its shape and size, and in some instances, improve ornamental qualities, it is important to prune young trees correctly to develop a strong framework of evenly spaced branches. The degree of pruning and training depends on the type of tree and desired effect, relatively little is required to produce a well-balanced tree whereas creating a pleached avenue with interwoven branches demands considerably more work and expertise. When to Prune; Most deciduous trees are best pruned when dormant in late autumn or winter, they may be pruned at other times, except in late winter or early spring when many trees “bleed” (exude sap) if cut; Maples (Acer), Horse chestnuts (Aesculus), Birches (Betula), Walnuts (Juglans), and Cherries (Prunus) all “bleed” extensively, even towards the end of their dormant season, prune these in mid-late summer after the new growth has matured. Evergreens need little or no pruning except for the removal of dead or diseased branches in late-summer. The Principals of Pruning; Always wear strong, protective gloves when pruning. The first stage is to remove any dead, diseased, or damaged wood on the tree, and to cut out any weak or straggly shoots, then assess the remaining framework and decide which branches should be pruned back or removed for well balanced-growth. Take care not to impair the natural growth habit of a tree by pruning unless aiming to produce a certain shape or form, such as an espalier, hard pruning stimulates vigorous growth whereas light pruning produces only a limited growth, it is important to make pruning cuts accurately to minimize damage to the tree. If cutting back a stem, cut just above a healthy bud, pair of buds, or side shoot pointing in the required direction of growth, for example, if thinning out congested stems, cut back to a bud or shoot that is growing outwards, so it will not rub against another stem as it grows, cut neither too far from the bud, which leaves a stub that provides an entry point for disease, nor too close to the bud which could damage the bud itself. When pruning trees with opposite buds, make a straight cut with secateurs directly above a pair of buds, for trees with alternative buds, make a slopping cut 3-5mm (1/8-1/4in) above the/a bud so that the base of the cut is just level with the top of the bud, on the opposite side of the stem. If pruning a branch completely back, cut just outside of the branch collar; the slight swelling on the branch where it joins the trunk, this is where the callus is formed that will eventually cover the wound. Never cut flush with the main stem as this damages the trees natural protective zone, making it more vulnerable to disease. The branch collar on dead branches may extend some way along the branch, but it is still important to make any cut outside of it (the collar). Removing a Branch; If removing whole branches of less than 2.5cm (1in) in diameter, make a single cut with a pruning saw or secateurs, for branches thicker than this, first remove the bulk of the weight; partially undercut the branch atleast 30cm (12in/1ft) from the trunk, then a little further out saw through from above, if no undercut is made, the branch may break off in mid-cut ripping the bark back to the trunk, so making the tree vulnerable to infection. To remove the remaining stub, undercut it just outside the branch collar, then cut through from above. If you find it difficult to locate the branch collar, cut through the stub at a short distance from trunk, making the cut so that it slopes outwards away from the tree. If the angle between the branch and tree is very acute, it may be easier to cut through the stub from beneath. Do not apply a wound paint or dressing, as there is no clear evidence that they speed-up the healing process or prevent (and/or guard against) disease. Formative Pruning; Young trees benefit from formative pruning to ensure that they develop a strong, well balanced framework of evenly spaced branches. At its simplest, this involves the removal of dead, damaged, and diseased wood, as well as any weak or crossing branches/shoots. Formative pruning may also be used to determine the trees shape as it grows, for example; a young feathered tree may be pruned over several years to form a standard, or trained against a wall as an espalier, the extent of pruning depends on both; the type of tree selected and the required shape when mature, as with all types of pruning, care should be taken not to spoil the trees natural growth characteristics. It is particularly important to prune young tropical trees as their growth is very rapid and the girth of both the main stem and branches develops extremely quickly, provided that they are/have been pruned correctly during the first few years after planting, they may then be left to grow naturally. Most other evergreens on the other hand, will develop naturally into well-shaped specimens with little or no attention; pruning is usually restricted to the removal of dead, diseased, damaged, or crossing stems, and badly placed laterals. The formative pruning of ornamental garden trees depends on the type of tree bought or required; feathered trees have a single, central-leader and laterals along the whole length of the stem. Central-leader standards have a clear length of stem at the base, while Branched-head standards also have a clear stem but have their central-leader removed to encourage the formation of vigorous lateral branches, as commonly seen in many Japanese Cherries (Prunus). Feathered Trees; Feathered trees may either be simply pruned to enhance their natural shape or more extensively pruned to train them into standards, this process also happens/occurs naturally sometimes. Although many feathered trees retain their lower branches, these die back in some species and the tree ultimately becomes a central-leader standard, other trees may also lose their central-leader dominance and so become branched-head standards. Early training is straight forward, however, regardless of the eventual habit of the tree, first remove any competing shoots to leave a single main leader, and then take out any small, weak and poorly placed laterals so that the framework of the branches around the main stem is evenly spaced and well balanced. Central-Leader Standards; Feathered whips may be pruned over two to three years (2-3yrs) to form a standard; a technique called “feathering” is often used as it also channels food to the main stem which thickens and becomes sturdier. Initially, prune a feathered whip to remove any competing leaders or weak laterals, then, on the lowest-third of the tree, cut back all the feathers to the main stem, on the middle-third, reduce the feathers by about half, leave the top-third un-pruned, but remove any vigorous upright shoots that might form a competing leader. In late autumn or early winter, cut back the pruned laterals flush with the main stem, repeat the procedure over the next/following two to three years (2-3yrs) to form a tree approximately 1.8m (6ft) of clear stem. Branched-Head Standards; To form a branched-head standard, train the tree initially as a central-leader standard to achieve the desired length of clear stem, then, in mid to late autumn, cut back the leader to a strong, healthy bud or shoot to leave a framework of four or five strong, well-placed lateral branches, at this stage, also remove any crossing or congested laterals and any that spoil the balance of the branch framework. In subsequent years, prune the tree as much as necessary to keep the crown well-balanced and with an open centre, remove any vigorous, vertical shoots that may grow into a new leader and cut back any feathers to the main stem as soon as possible. Some branched-head standards can be formed by top-working (or top grafting) as for weeping-standards. Weeping-Standards; A weeping-standard is formed by grafting one or two scions of a weeping cultivar onto a stock-plant with a clear stem of about 1.8m (6ft), this is known as top-working (or top-grafting), a technique that is commonly used for fruit trees, but also for weeping ash (Fraxinus excelsior “Pendula”), the Kilmarnock willow (Salix caprea “Kilmarnock”), and a large number of other weeping ornamental trees. Young pendulous branches start to develop once the grafts have taken (successfully joined). Pruning is best restricted to the removal of crossing or vertical branches as well as any that spoil the overall symmetry of the framework, although upwards-growing branches are usually removed, leave some semi-upright stems to develop naturally as they often grow downwards later and produce tiers of weeping branches, if growth appears on the main stem, rub or pinch them out as soon as they appear. Espalier and Fan-Trained trees; The aim of both espalier and fan-training is to form a symmetrical, attractive network of branches in a single plane by pruning and training a young tree over several years. These techniques are occasionally used for growing ornamental trees against fences or walls, but they are more commonly associated with growing fruit trees. Pruning times vary according to the selected species, for example; Magnolia grandiflora, which flowers from mid to late summer, should be pruned at the start of the growth in spring, while the spring-flowering Acacia dealbata should be pruned directly after flowering. Note; All information given coincides with the guidelines of the Royal Horticultural Society (RHS).
Posted on: Sun, 07 Sep 2014 19:16:28 +0000
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