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 controling 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, both gardeners and orchardists, often argue that it improves the health of the plant and makes sturdier structure, often referred to as the scaffold; opponents believe that pruning harms plants' "natural" forms.
Types of pruning
From the least to the most severe forms of pruning:
- Pinching: Removing new buds or growth of herbaceous plants in order to control growth. This is the least damaging method for pruning and is the first opportunity to control the plant, encouraging bushiness or height in a plant by removing its terminal growth or lateral growths, respectively. For instance, pinching off the terminal buds of herbaceous plants, such as chrysanthemums encourages denser growth and more profuse or delayed flowering.
- Dead Heading: A form of pruning used on small to medium flowering shrubs to remove spent flowers. This is a common method used on Roses. The practice of "deadheading" is also a type of pinch pruning: it removes spent flowers before they begin to set seed, to concentrate a plant's energy on continued flower production, for the current year or the following year, as when lilacs are dead-headed after flowering.
- Shearing: A form of pruning employed on hedges or topiary, in which most of the growing points are tipped back, to produce artificially dense growth. Shearing in general is a more indiscriminate form of pruning, where the plant is simply cut to shape, however plants that have been trained to be sheared generally produce buds and on the "surfaces" where they are to be sheared. It is commonly performed with hedge trimmers.
- Cutting-back: 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 which involves removing entire branches. 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 simplifying and "opening-up" the branching of neglected trees, or for renewing shrubs with multiple branches like Forsythia or Spirea.
- Heading: Heading 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 performmed correctly, heading can be used to begin training younger trees for pollarding. When heading a tree down to a stump, the technique is called coppicing. When heading is performed incorrectly or on old trees, the result is at best a non-aesthetically pleasing tree crown or, at worst, the death of the tree.
Technique
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 an infection.
Time period
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 instea d. 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.