Pruning in landscaping and gardening is the practice of removing diseased, non-productive, or otherwise unwanted portions from a plant. The purpose of pruning is to shape the plant by controlling or directing plant growth, to maintain the health of the plant, or to increase the yield or quality of flowers and fruits. Proper pruning is as much a skill as it is an art, since badly pruned plants can become diseased or grow in undesirable ways.
Proponents of pruning often argue that it improves the health of the plant and makes sturdier structure, opponents believe that pruning harms plants' "natural" forms and leads to wounding which may become infected.
In general the smaller the wound (smaller the branch that is cut) the less harm to the tree. It is therefore better to formative prune the tree when juvenile than try to cut off large branches on a mature tree.
There are also inconsistencies pertaining to pruning. How you would prune a rose, shrub, hedge, fruit tree and an amenity tree may be different.
Consequences with incorrect pruning performed to large trees can be dangerous. If a shrub was incorrectly pruned and a piece broke off it may not do much damage. However if a tree next to the house was incorrectly pruned and a large branch fell from 50' it could be deadly.
Pruning Landscape and Amenity Trees
Branch structure and how they are attached to each other in trees falls into 3 categories. Collared unions, collarless unions and codominant unions. Each specific attachment has its own unique way of being cut so that the branch has less chance of regrowth from the cut area and best chance of sealing over and compartmentalising decay. This means that there are 3 types of cuts made, whether that be to remove a little branch coming of another or cutting a whole branch off back to the trunk. This term is often referred to by arborists as "target cutting".
Some of the terms used predominantly by arborists and what they entail:
Removal of dead and decaying branches from the tree to minimise the risk of damage to property/injury to people.
Crown – Canopy thinning
Increase light and reduce wind resistance by selective removal of branches throughout the canopy of the tree. This is a common practice which improves the tree's strength against adverse weather conditions as the wind can pass through the tree resulting in less "load" being placed on the tree. Generally performed on trees that do not have a dense impenetrable canopy as opening a 100% dense canopy up with holes for wind to enter can result in broken branches and uprooting.
Crown canopy lifting
Removal of lower branches. Increase clearance for property, people and vehicles.
Directional or Formative Pruning
Removal of appropriate branches to make the tree structurally sound whilst shaping it.
Selectively pruning a window of view in a tree.
Reducing the height and or spread of a tree by selectively cutting back to smaller branches.
A regular form of pruning where certain deciduous species are pruned back to pollard heads every year in the dormant period. This practice is commenced on juvenile trees so they can adapt to the harshness of the practice.
Types of pruning
Regardless of all the various names used for types of pruning there are only two basic cuts. 'One cuts back to an intermediate point, called heading back cut' and the other cuts back to some point of origin, called thinning out cut.
Removing a portion of a growing stem down to a set of desirable buds or side-branching stems. This is commonly performed in well trained plants for a variety of reasons, for example to stimulate growth of flowers, fruit or branches, as a preventative measure to wind and snow damage on long stems and branches, and finally to encourage growth of the stems in a desirable direction. Also commonly known as heading-back.
- Thinning: A more drastic form of pruning, a thinning out cut is the removal of an entire shoot, limb, or branch at its point of origin. This is usually employed to revitalize a plant by removing over-mature, weak, problematic, and excessive growths. When performed correctly, thinning encourages the formation of new growths that will more readily bear fruit and flowers. This is a common technique in pruning roses and for implifying and "opening-up" the branching of neglected trees, or for renewing shrubs with multiple branches.
- Topping: Topping is a very severe form of pruning which involves removing all branches and growths down to a few large branches or to the trunk of the tree. When performed correctly it is used on very young trees, and can be used to begin training younger trees for pollarding or for trellising to form an espalier.
- In orchards, fruit trees are often lopped to encourage regrowth and to maintain a smaller tree for ease of picking fruit. The pruning regime in orchards is more planned and the productivity of each tree is an important factor.
Deadheading is the act of removing spent flowers or flowerheads for aesthetics, to prolong bloom for up to several weeks or promote rebloom, or to prevent seeding.
The general rule to pruning is to always cut in a location where growth will occur, whether the cut is next to a bud or another branch. Cutting a branch beyond where growth will occur effectively kills all portions of that branch back to the closest branch, bud, or dormant bud clusters, leaving a stub of dead wood. The withered stub will eventually rot away and fall off. Prior to that, however, it will prevent the plant from forming a callus over the cut surface, which will in turn invite insects and infection. All cuts should be relatively smooth since this will aid in healing.
Also, the pruning cut should not be too large when compared to the growing point. For instance, a large cut on a 20 cm trunk down to a 15 cm branch should be fine, but the same cut to the trunk down to a 1 cm twig or bud is considerably less ideal and should be avoided if possible.
Pruning to bud
A correct pruning cut will allow for quick healing and promote vigorous growth from the closest bud to the cut. The cut should be close enough to the bud to reduce the size of the stub of dead wood that will form from the cut, but far enough away to prevent the bud from being adversely affected by the cut though desiccation. Cutting too close to the bud (under-cutting) sometimes results in the death of the bud, which results in a scenario similar to cutting too far away from the bud (over-cutting). In general, a correct cut should be angled at a moderate 35-45 degree slant such that its lowest point is situated on the same level as the tip of the growth bud. This technique is usually applied when pinching or when cutting-back.
Pruning to a main branch
The pruning cut should occur slightly away from and follow the branch collar. When cutting away branches growing directly from the roots, the cut should be flush and level to the ground. This technique is usually applied when thinning or to remove larger dead or damaged branches.
When using pruning shears or loppers to remove a branch back to a main branch, the "hook" portion of the shears should always face away from the main branch. This ensures that the blade will not leave a protruding stub and the hook will not damage the branch collar or parts of the main branch.
Large heavy branches
Depending on the weight of the branch, the first cut should be a notch on the underside of the branch about a third to half of the way through. The bulk of the branch should then be removed with a follow-through cut slightly above the first cut, thus leaving a limb stub. The purpose of this is to stop the weight of the branch from tearing the bark of the tree from the underside, which would normally occur if the removal was done with one cut. The limb stub ensures that any cracking of the wood resulting from the branch separation is limited to the portion of the wood to be removed.
The branch collar should then be located, and can be identified by the strip of rough bark running down from the topside of the branch at its junction with the stem. The cut for removing the limb stub should be just outside the branch collar, leaving a small bump. The bump and the branch collar should not be removed since this action can reduce healing time, which could result in a major infection.
Pruning small branches can be done at any time of year. Large branches, with more than 5-10% of the plant's crown, can be pruned either during dormancy in winter, or, for species where winter frost can harm a recently-pruned plant, in mid summer just after flowering. Autumn should be avoided, as the spores of disease and decay fungi are abundant at this time of year.
Some woody plants that tend to bleed profusely from cuts, such as maples, or which callous over slowly, such as magnolias, are better pruned in summer or at the onset of dormancy instead. Woody plants that flower early in the season, on spurs that form on wood that has matured the year before, such as apples, should be pruned right after flowering, as later pruning will sacrifice flowers the following season. Forsythia, azaleas and lilacs all fall into this category.
Fruit tree pruning
Pruning fruit trees is a technique that is employed by gardeners to control growth, remove dead or diseased wood or stimulate the formation of flowers and fruit buds. The most economical pruning is done early in the season, when buds begin to break, and one can pinch off the soft tissue with one's fingers (hence the expression "nipped in the bud"). Many home fruit growers make the mistake of planting a tree, then neglecting it until it begins to bear. But careful attention to pruning and training young trees will ultimately determine their productivity and longevity. Good pruning and training will also prevent later injury from weak crotches that break under snow or fruit load.
To obtain a better understanding of how to prune plants properly, it is useful to have some underlying knowledge of how pruning works, and how it affects the way in which plants grow.
Plants form new tissue in an area called the meristem, located near the tips of roots and shoots, where active cell division takes place. Meristem growth is aimed at ensuring that leaves are quickly elevated into sunlight, and that roots are able to penetrate deeply into the soil. Once adequate height and length is achieved by the stems and roots, they will begin to thicken to give support to the plant. On the shoots, these growing tips of the plant are known as apical buds. The apical meristem (or tip) produces the growth hormone auxin, which not only promotes cell division, but also diffuses downwards and inhibits the development of lateral bud growth which would otherwise compete with the apical tip for light and nutrients. Removing the apical tip and its suppressive hormone allows the lower dormant lateral buds to develop, and the buds between the leaf stalk and stem produce new shoots which compete to become the lead growth.
Manipulating this natural response to damage (known as the principle of apical dominance) by processes such as pruning (as well as coppicing and pollarding) allows the horticulturist to determine the shape, size and productivity of many fruiting trees and bushes. The main aim when pruning fruit trees is usually to obtain a decent crop of fruit rather than a tree with an abundance of lush yet unproductive foliage. Unpruned trees tend to produce large crops of small, worthless fruit often damaged by pests and diseases, and much of the crop is out of reach at the top of the tree. Branches can become broken by the weight of the crop, and the cropping may become biennial (that is, only bearing fruit every other year). Overpruned trees on the other hand tend to produce light crops of large, flavourless fruit that does not store well. Pruning is therefore carried out to achieve a balance between shoot growth and fruit production.
Formative pruning of bush trees
Formative pruning of apple (Malus pumila) and pear (Pyrus communis) trees (the pome fruits; the stone fruits such as cherries, plums, gages, etc., have different requirements and should not be pruned during the dormant months) should be carried out during the dormant winter months between November and March (or June and September in the southern hemisphere) and during the early years of the tree's life to develop a strong framework capable of bearing the weight of the crops that will be borne in later years. This involves hard pruning, although in later years pruning will be lighter and carried out to encourage fruiting.
A maiden whip (that is, a one year old tree with no side shoots) should be pruned to a bud with two buds below it at about 80 cm from the ground immediately after planting to produce primary branches during the first growing season. A feathered maiden (that is, a one year old tree with several side branches) should have its main stem pruned back to three or four strong shoots at 80 cm from the ground. Side shoots should be shortened by two thirds of their length to an upward or outward facing bud. Lower shoots should be removed flush with the stem.
Remove any lower shoots and prune between three and five of the best placed shoots by half to an upwards or outwards facing bud to form what will become the tree's main structural branches. Remove any inwards facing shoots.
Prune the leading shoots of branches selected to extend the framework by half to a bud facing in the desired direction. Select four good laterals to fill the framework and shorten these by a half. Prune any remaining laterals to four buds to form fruiting spurs.
The tree will have begun to fruit and only limited formative pruning is now required. Shorten leaders by one third and prune laterals not required to extend the framework to four buds.
Five year and onwards
The tree is considered to be established and should be annually pruned as described in
Pruning the cropping tree
Before pruning it is important to distinguish between spur bearing and tip bearing varieties. The former, which is the most common type, bear most of their fruit on older wood, and include apples such as Cox's Orange Pippin, James Grieve and Sunset, and pears such as Conference, Doyenne du Commice and Williams Bon Chretien. Tip bearers on the other hand produce most of their fruit buds at the tips of slender shoots grown the previous summer, and include the apples Worcester Pearmain and Irish Peach, and the pears such as Jargonelle and Josephine de Malines. There are basically three types of pruning that are applied once the main shape of the tree has been established. These are:
Spur pruning:Spur bearing varieties form spurs naturally, but spur growth can also be induced.
Renewal pruning: This also depends on the tendency of many apple and pear trees to form flower buds on unpruned two year old laterals. It is a technique best utilised for the strong laterals on the outer part of the tree where there is room for such growth. Pruning long neglected fruit trees is a task that should be undertaken over a lengthy period, with not more than one third of the branches that require removal being taken each year.
Regulatory pruning: This is carried out on the tree as a whole, and is aimed at keeping the tree and its environment healthy, eg, by keeping the centre open so that air can circulate, removing dead or diseased wood, preventing branches from becoming over crowded (branches should be roughly 50 cm apart and spurs not less than 25 cm apart along the branch framework), and preventing any branches from crossing.
Pruning of tip bearers
Tip bearers should be pruned lightly in winter using the regulatory system (see above). any maiden shoots less than 25 cm in length should be left untouched as they have fruit buds at their tips. Longer shoots are spur pruned to prevent over-crowding and to stimulate the production of more short tip bearing shoots the following year. Branch leaders are 'tipped', removing the top three or four buds to a bud facing in the desired direction to make them branch out and so produce more tip bearing shoots.