Pruning, which has several definitions, involves removing plant parts to improve the health, landscape effect or value of the plant.
In nature, pruning involves the removal or reduction of certain parts of the plant that are no longer effective or are no longer of use to the plant. It is done to supply additional energy for the development of flowers, fruits and limbs that remain. Every plant eventually is pruned in some manner through the loss of branches and leaves. A plant growing naturally assumes the shape that allows it to make the best use of light in each location and climate.
Human pruning is the selective removal of plant parts to achieve a specific goal. Any pruning you perform should be for a definite reason and should remove no more than necessary to achieve your objective. Often people fail to realize that many trees and shrubs require little pruning to thrive and achieve good form.
How Woody Plants Grow
To understand the best pruning methods for woody plants, you must understand how they grow. The portion of the trunk or branch that can actively grow consists of a small layer, just inside the bark called the cambium.
When you are pruning, you leave a wound that consists mostly of the main woody part that cannot grow and therefore cannot heal itself. Healing must start from the edge of the wound, where the cut came across the cambium. The cambium grows over the wound from the outside in with a special kind of growth called callus.
Because of this pattern, larger wounds take far longer to heal than smaller ones and remain vulnerable to infection longer. Your pruning choices should take this into account and minimize the size of the cuts you make. In practice, this means not only selecting the smallest possible branches to cut. Another thing to remember is that terminal buds (buds at the end of a branch or stem) suppress the growth of buds lower on the branch.
Thus, pruning that removes the terminal bud allows remaining buds to grow. Therefore, pruning larger branches at the end often releases many dormant buds lower on the branch, resulting in a mass of new shoots.
The spot from which leaves, buds and lateral shoots arise is called the node. The space on the stem between nodes is the internode. This arrangement is easy to see on young shoots but becomes obscure on older branches.
Pruning also removes carbohydrate reserves stored in wood, as well as foliage, which produces additional carbohydrates through photosynthesis. Removing these food sources reduces the plants ability to support its root system, which may dieback if you remove too many branches and shoots. A tree may require several years to recover from severe pruning and the resulting stress makes it more vulnerable to pests, diseases and environmental extremes.
When to Prune
Pruning can be done at any time of the year; however, recommended times vary with different plants. Contrary to popular belief, pruning at the wrong time of the year does not kill plants, but continual bad pruning results in damaged weakened plants. Try pruning when there is the least chance of damage.
In general, the best time to prune most plants is during late winter or early spring before growth begins. There are exceptions to this rule but the above is the best idea to keep in mind, the least desirable time is immediately after new growth develops in the spring. A great amount of food stored in roots and stems is used in developing new growth. This food should be replaced by new foliage before its removed, if not, considerable dwarfing of the plant may occur, a common problem encountered in pruning.
It’s also advisable to limit the amount of pruning done late in the summer as new growth may be encouraged in some plants. This growth may not have enough time to harden off before cold weather arrives resulting in cold damage. Prune plants damaged by storms, vandalism or ones with dead limbs as soon as possible to avoid additional insect and disease problems that may develop.
Knowing and practicing proper pruning techniques is very important, but equally important is using the correct tools. Equipment can be limited to a few items if the proper ones are selected. Make sure to select tools that will do the job, keep a sharp edge and are relatively easy to sharpen and handle. Some of the most commonly used pruning tools are shown in this section below.
Good equipment that is properly cared for will do a better job and lasts longer. Store equipment in a dry room, keep it sharp and in good operating condition. When pruning diseased plants, disinfect all shears and saw blades after each cut to prevent spreading disease to healthy plants. Use alcohol or bleach to disinfect equipment between each cut when pruning diseased plants. Mix at the rate of one-part bleach to nine parts water. At the end of the day, oil pruning equipment to avoid rusting.
There are many types of hand pruning shears. Most of them are designed for cutting stems up to ½ inch in diameter. Attempting to cut larger branches risks making a poor cut and/or running the sheers.
Two common styles of hand shears are the scissor action and the anvil cut; we recommend using scissor blades because they make cleaner, closer cuts.
Lopping shears (loppers) have long handles that are operated by both hands. Even the least expensive loppers can cut material ½ inch in diameter. Better ones can slice through branches of 2 inches or more, depending on the plant species (i.e. oak branches are tougher than ash tree) and condition (i.e. dead wood is tougher than live wood until decay sets in).
Pole pruners usually have a cutter with one hooked blade above and a cutting blade beneath, similar to a large pair of lopping shears. The cutter is on a pole and is operated by pulling a rope downward. Poles can be made of several materials and can either be in sections that fit together or that telescope. Wooden poles are sturdy but heavy, while aluminum poles are light but can conduct electricity if they touch an overhead electrical wire.
Fiberglass or some type of plastic compound is probably the best pole material. Poles can be fitted with saws, but these are usually very frustrating to use. Use of pole pruners can be dangerous, material overhead can fall on the operator, the user should exercise caution and wear head and eye protection.
Hedge sheers are mainly used for shearing plants into hedges or formal shapes. The most common type is manually operated; however, if large areas of hedges are involved, power-driven shears may be more practical.
Pruning saw, both rigid and folding, are very useful for cutting larger branches that are too large for hand shears; tree saws are available for removing large tree branches. Pruning saws usually cut on the pull stroke and are preferred over a carpenter’s saw because they cut faster and easier. Saws are only good to use where no obstructions exist for at least a foot or more above the area to be cut.
Gas powered and electrical chain saws come in a variety of sizes. They are best suited for removing trees and cutting firewood but can also be used to prune live plant material. Only professional arborists should use power saws for pruning up in trees because of safety concerns.
Each cut area of a plant or tree is considered a type of wound, much has been written about the advantages and disadvantages of using a wound dressing on large cuts. Traditionally, would dressing or pruning is used only on cuts larger than an inch in diameter, however, scientists have found that wound dressings are strictly cosmetic and have little to do with preventing insect or disease damage to the wounded area. Pruning paint may slow down the healing process, but in general, wound dressings are not recommended or necessary.
Correct Pruning Cuts
To encourage rapid healing of wounds, make all cuts clean and smooth. This requires good, sharp, pruning equipment. Avoid tearing the bark when removing large branches, the following provides some specifics on pruning techniques.
To properly prune you must first understand the arrangement of the buds on the twigs or branches. As mentioned before, buds are the part of the plant that turns into a flower, leaf or shoot. They are arranged either as alternating opposite, directly opposite or in a spiral (a bunch of buds at the same place around the twig.
The position of the last pair of buds will always determine the direction in which the new shoot will grow. Buds on top of the twig will probably grow upward at an angle and to the side on which it is directed. In most instances it's advisable to cut back each stem to a bud or branch. Selected buds that point to the outside of the plant are more desirable than buds pointing to the inside. By cutting an outside bud, the new shoots will grow outward and not inward towards the plant.
When cutting back to an intersecting (lateral) branch, choose a branch that forms an angle of no more than 45 degrees with the branch to be removed. Also, the branch that you cut back to should have a diameter of at least half that of the branch to be removed. Make slanting cuts when removing limbs that grow upward; this prevents water from collecting in the cut and expedites healing.
To “open” a woody plant, prune out some of the center growth and cut back to the buds that point outward. In shortening a branch or twig, cut it back to a side branch and make the ½ inch above the bud. If the cut is too close to the bud, the bud usually dies. If the cut is too far from the bud, the wood above the bud usually dies, causing dead tips on the end of the branches.
When the pruning cut is made, the bud or buds nearest to the cut usually produce the new growing point. When a terminal bud is removed, the nearest side buds grow much more than they normally would and the bud nearest the pruning cut becomes the new terminal bud. If more side branching is desired, remove the tip of all limbs.
The strength and vigor of the new shoot is often directly proportioned to the amount the stem is pruned back since the roots are not reduced. For example, if a deciduous shrub is pruned to 1 foot from the ground, the new growth will be vigorous with only a few flowers the first year. However, if only the tips of the old growth are removed, most of the previous branches are still there and new growth is shorter and less vigorous. Flowers will be more plentiful although smaller. This, if a larger number of small flowers and fruits are desired, prune lightly. If fewer, but high-quality blooms or fruits are wanted in succeeding years, prune extensively.
Cutting Thick and Heavy Branches
Thick and heavy branches should be removed flush to the collar at the base of the branch, not flush with the trunk. The collar is an area of tissue of the branch that is chemically protected. In the natural decay of a dead branch, when the decay advances down the branch it meets the internal protected area of the collar. Here the branch falls away; this is the natural shedding process when all goes according to nature’s plan. If the collar is removed, the protective zone is removed, causing a serious trunk wound. Wood-decay fungi can then easily infect the trunk. If the pruned branch is living, removing the collar at the base still causes injury.
When cutting the branches more than 1 ½ inches in diameter, use a three-part cut. The first step is to saw an undercut from the bottom of the branch about 6 to 12 inches out of the trunk and about one third of the way through the branch. Make a second cut from the top, about 3 inches further from the undercut, until the branch falls away. The resulting stub can then be cut back to the collar of the branch. If there is danger of the branch damaging other limbs or objects on the ground, it should be properly roped and supported, then carefully lowered to the ground.
Topping vs. Thinning
All too often trees are topped to reduce size or to rejuvenate growth. In either case, topping is not a recommended practice; in fact, some refer to it as the “Texas Chainsaw Massacre.” Topping is the process where a tree is cut back to a few large branches. After 2 to 3 months, regrowth on a topped tree is vigorous, bushy and upright. Topping seriously affects the tree’s structure and appearance. The weekly attached regrowth can break off during severe wind or rainstorms. Topping may also shorten the life of a tree by making it susceptible to attack by insect and disease.
Thinning is a better means of reducing the size of a tree or rejuvenating growth. In contrast to topping, thinning removes unwanted branches by cutting them back to their point of origin. Thinning conforms to the tree’s natural branching habitat and results in a more open tree, emphasizing the branches’ internal structure. Thinning also strengthens the tree by forcing diameter growth of the remaining branches.