Pruning Principles
By Brian Marshall
Pruning is a key element in caring for the trees and shrubs in a landscape. If done well, it can improve the health and longevity of plants and the overall appearance of your garden. If done incorrectly, trees and shrubs can be forever ruined.
Proper pruning is not an exact science, but pruning approaches and techniques are derived from an understanding of horticulture. Knowledge about the specific growth habits and needs of the plants being pruned, along with a good eye for balance and symmetry, will go a long way toward yielding outstanding pruning results.
Following are general principles of pruning, on which the many ‘rules’ of pruning are built. Learn these concepts first — then it will be easier to apply specific rules and techniques for best results.
1. Safety first and always. Pruning employs sharp and sometimes dangerous tools. It can require getting into awkward and hazardous positions. Know your capabilities and limits.
Just because you own a chain saw or other power equipment doesn’t mean you have the capability to cut heavy or overhead branches. Pruning of large trees or at heights should normally be left up to trained professionals with bucket trucks and climbing equipment. Do not prune near electrical or utility wires.
Make sure to use appropriate protective gear for whatever pruning tasks you undertake – safety goggles, ear protectors, work gloves, sturdy shoes, and even a hard hat when working overhead.
2. Prune with a purpose. If selected, positioned, and planted properly, there are many trees and shrubs that will need very little pruning. That means the call for pruning is not automatic, and should not be undertaken unless there is a specific reason to do so.
Yet, there are many good motivations for pruning, such as to a) remove hazards like dead or low limbs, b) remove diseased limbs and tissue, c) remove problem, crossing and weak limbs and suckers, d) train plant growth for optimal shape, e) restrict growth, f) maintain plant health and vigor, g) enhance flower, fruit and foliage quality, h) encourage air circulation, i) improve shape and overall appearance, and j) renewal, renovation and rejuvenation.
So, before you start, choose your purpose or purposes for pruning, and you will more likely accomplish your objectives.
3. Understand each plant’s essentials. Some of the important plant qualities to understand before pruning are a) growth habit and peak growing seasons, b) bloom and flower bud formation seasons, c) blooming from this year’s new growth or from buds formed on last year’s growth, d) new leaf/needle growth along older branches or only from branch tips, e) secondary blooms after deadheading, or not.
Successful pruning needs to work with the natural habit of the woody plant, not against it. It’s very difficult to successfully turn a tree into shrub form if the plant’s natural habit is to grow like a tree. The typical result is a severely weakened plant that never again looks right – and then it dies.
Bud formation (location and timing) defines many of the nuances of how plants grow their leaves or needles and how and when they flower. A common reason novice pruners complain that their shrubs didn’t bloom as well as in the past is because they either pruned at the wrong time or they cut off the flowering buds that had already formed last year.
4. Work with a plan. Know what you plan to cut before you start. That can mean the type of branches and shoots to cut, how much, at what type of branch junction, and even which specific branches. It is important to consciously identify how much plant material will be removed and what the plant will look like when you are done.
With your plan in mind, work logically, methodically, and relatively slowly. Make sure the branch you are cutting is the one planned. If you are unsure of a cut, it is better to remove a branch in smaller sections to see the effect. It is always possible to cut more off with another cut, but once cut it is impossible to put a branch back. As you progress, pause often and step back to check the overall effect on the tree or shrub. Adjust the plan and approach as needed based on the observations you make.
Consider the order in which pruning cuts are made, especially on very dense and severely overgrown plants. Starting with dead, diseased or broken limbs (which need to be removed in any case) can enable your plan to begin taking shape quickly and reveal other pruning cuts that are needed. Next, remove crossing, damaged, weak and other problem branches, along with competing main stems, suckers and water sprouts; this often accomplishes most of the interior thinning required. Finish by making any desired training and other corrective cuts for current shaping and for the desired future growth profile.
When restoring overgrown plants to a previous (and natural) shape and size, it is crucial to both understand the plant essentials (Principle #3) and to follow a plan. In many instances, the amount of wood and plant tissue that must be cut out to fully restore a severely overgrown plant is more than can be safely removed in one pruning episode, so the plan needs to be created and implemented over several growing seasons.
5. Use proper and well-maintained tools. Pruning is surgery, so the tools chosen to make cuts need to be precision instruments and kept very sharp. While there can be a need for power chain saws to cut large branches, most pruning work is properly performed with only manual pruners, loppers, and pruning saws.
Unless you are maintaining a large, formal hedge, there is no reason to use power hedge trimmers. Even then, it is better to use scissor-action, manual hedge shears, because power trimmers rip and tear plant tissue and twigs, which is damaging to the plant.
Keep your pruners and loppers sharp and clean for good results. Most manual tools can be taken apart, sharpened with a blade tool and reassembled easily, so there is no reason to let them become dull. Use safety precautions when sharpening, including securely gripping the blade in a table vice, wearing gloves and eye protection (Principle #1). Clean and disinfect your tools at the end of every use to keep them in good working order and to prevent spreading diseases during future pruning efforts.
6. Prune for the benefit of the plant. It may be most convenient to prune your trees and shrubs around your personal schedule, but the best horticultural results are created when pruning times are chosen by what is best for plant health and vigor, and by what will cause the least damage to the plants.
There are certain types of pruning that can be performed at any time, such as removing dead or diseased limbs. In reality, you can usually prune other branches throughout the year without killing the tree or shrub. However, repeated pruning during the wrong season can damage or weaken the plant’s structure.
There are some exceptions, but a good time to prune many plants is during their dormant period in late winter before spring growth begins. But as soon as the new growth emerges, it becomes one of the worst times to prune, because the food and energy stored in the branches is pruned away before the new leaves can begin generating new food and energy.
Many plant species have very specific times that are best for pruning that will match up with growth periods and bud formation. To prune these plants during the wrong season may interrupt their natural growth habit and may prevent them from flowering and fruiting in following years. Pruning too late in the summer or early fall can trigger late growth that does not have enough time to harden off before winter leading to winter burn and other cold weather damage.
7. Prune the correct amount. A general rule-of-thumb is not to cut out more than one-third of the plant material, whether you are thinning, removing branches, or removing multi-stemmed shrub stalks. But that can be way too much or way too little depending on the plant species and the type of pruning you are doing. To cut out one-third of a large tree could be extremely harmful, and to only cut out one-third may not accomplish complete rejuvenation if that’s the goal.
Keeping the one-third rule in mind is useful in preventing going too far during any pruning effort. For badly overgrown shrubs, this limit helps plan the pruning effort and to decide if pruning goals should be spread out over several growing seasons. Pruning the correct amount is also a reminder that it is better to remove branches with several sequential cuts to ensure that too much material is not removed.
8. Make good cuts. A good, clean cut is made with a sharp blade (pruners or loppers) in the right place at the correct angle, creating the least damage to plant tissue that can be readily healed by the plant itself. A typical branch cut is located either at its base (trunk or lateral branch), or at an intersecting lateral branch, or just above a lateral bud. Cut back to the branch collar when cutting to the base. When cutting to an intersecting branch, the branch remaining should best be at a 45 degree angle to, and half as large in diameter as, the branch removed. Cuts should be made about ½ inch above the intersecting branch or last bud, and at a 45 degree angle in the direction of the remaining branch or last bud.
The least damage is created by using proper and well-maintained tools (Principle #5). Furthermore, it is important to use a correctly sized tool for the branch being cut. Trying to cut too large of a branch for the size of the tool often results in the blades being twisted, thereby crushing the bark at the cut and making it harder for the wound to heal.
When removing large branches with a saw (hand saw or chainsaw), it is important to undercut first, followed by a top cut, so that the bark beneath the branch doesn’t strip or tear off when it falls. A third, clean cut is made at the branch collar around the base of the branch. Cutting at the outside edge of the collar rather than flush at the trunk or down the branch will allow the wound to heal and to seal off the old branch tissue.
9. Pruning does not stand alone. Proper pruning is an important component of tree and shrub care, but it is not alone sufficient to maintain thriving plants. Of course, trees and shrubs also need adequate water and nutrients, the proper amount of sunlight, care of the soil and roots, plus protection from the elements (e.g., winter cold, wind and sun). That means scheduled pruning needs to be integrated into the overall seasonal care regimen designed for the overall health and longevity of each plant.
10. Pruning is not a one-time event. Pruning should begin when a tree or shrub is first planted, although the only cuts then should be broken, diseased, or damaged branches. Over time, selected training cuts will encourage vigorous growth and an appealing natural shape. Also over a number of years, the lowest branches on young trees can be removed to raise the canopy, while maintaining a strong structure.
Even after a major pruning, it is important to anticipate additional work during the following growing seasons. Sometimes that will be stage 2 of a multi-year effort, or sometimes it will be cleaning up new growth that was unanticipated at the time of the pruning. In all cases, the need for pruning should be evaluated on a regular, ongoing basis, so that only a modest amount of pruning will be needed in any given growing season.
