The Art and Science of Pruning

N. Jordan Franklin,
Consumer Horticulture Agent & Master Gardener Coordinator,
Clemson University Cooperative Extension Service

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Pruning trees and shrubs is an art and a science. From an artistic perspective, a discerning eye is needed to evaluate a plant, then determine what (if anything) must be done to achieve the desired appearance. From a scientific perspective, knowing the when, where, and how of pruning a plant is equally, if not more, important. However, it isn't necessary for a gardener to be an artist or a scientist to achieve quality results.

It could be argued the art of pruning begins before a plant is ever placed into the ground. Following a "Right Plant, Right Place'" approach to choosing plants for the landscape helps many gardeners avoid unnecessary and laborious pruning tasks. Why create a problem, when it could be avoided altogether? In using a "Right Plant, Right Place" approach, the gardener should consider the site in which the plant will be placed, and then choose the plant best suited for the space. Considerations for the mature size of the plant helps to prevent plants from overgrowing their space, getting too close to structures, covering windows, obstructing sidewalks, etc.

The art of pruning can also be found in the natural form of a plant. When gardeners become familiar with the natural form of the plants in their landscape, they are better equipped to understand how the plant should look. Individual tastes and desires factor into whether a gardener chooses to create a hedge or topiary with their garden plants. A finely-manicured hedge or topiary is more work than most gardeners have the time or patience to achieve. However, allowing plants to maintain their natural form and restricting pruning to only structural and emergency pruning will produce an attractive and low-maintenance landscape.

When considering the science of pruning, it's important to contemplate how pruning affects the plant. In essence, the activity of pruning causes damage and stress to the plant. In many instances, pruning is necessary to improve the health and productivity of a plant in the long term. However, a gardener should take all steps necessary to minimize the damage and stress to the plant when possible. A stressed plant is more susceptible to insect and disease attack, as well as drought and cold damage.

The science involved with properly pruned plants can be categorized into the "3 Ts of Pruning": Tools, Timing, and Technique. Purchasing quality tools is an important first step. When it comes to pruning tools, cheaper is not always better. Look for sturdy tools made from quality materials. Every gardener should have 3 essential pruning tools in their arsenal: hand pruners, pruning loppers, and a pruning saw. Hand pruners are used to cut branches ½ inch or smaller. Pruning loppers are for pruning branches between ½ and 1 ½ inch. When choosing pruners and loppers, purchase by-pass pruners which means that one blade "passes by" the other blade, similar to the cutting action of a pair of scissors. This type of pruner provides a more precise cut than do traditional anvil-type pruners. Finally, a quality pruning saw is needed for branches larger than 1 ½ inch. A gardener's individual style will determine whether shears (manual, gas, or electric), a chainsaw, and/or a pole saw are also needed.

Timing is the next "T" of pruning. There are general guidelines that gardeners can use to determine when to prune their trees and shrubs. When a plant is grown for its flower production, pruning time is based on when the plant flowers.

Plants that flower in the spring (prior to May) should be pruned immediately after flowering because most of these shrubs produce the following year's blooms during the summer. Pruning spring-blooming shrubs during the summer will result in cutting off many of the flower buds for the following spring.

Plants that flower in the summer (after May) should be pruned during late winter or early spring because they typically bloom on new growth. However, there are exceptions to this rule. Examples include oakleaf hydrangea, magnolia, and gardenia which bloom in June. These plants produce blooms on mature wood. Pruning them in late winter or early spring would remove many of the summer's blooms. Therefore, prune them immediately after flowering in June. For additional information on pruning hydrangea, see HGIC 1096, Pruning Hydrangeas.

In the case of plants not grown for their flowers, these can be pruned during late winter to early summer, as there is no concern for removing flower buds. No plants should be pruned from late summer to early winter. Pruning during this time can encourage flushes of new growth, which are unable to harden off appropriately and can be damaged by below freezing temperatures in early winter.

The final "T" of pruning is technique. Pruning technique is a subject worthy of its own dedicated writing, as there are many nuances of different techniques and the different plants on which those techniques are employed. However, when considering a pruning technique, there is a logical starting sequence for pruning any tree or shrub.

  1. Prune dead, diseased, and damaged wood at any time. Negligence in removing these problems could expose the plant to further attack by disease or insects. Depending on the situation, dead and damaged wood could cause a hazard to property and people with the risk of dead branches breaking free from a large shrub or tree and falling to the ground or onto structures below.
  2. Remove crossing branches that rub against each other. Removing one of these crossing branches helps to protect the plant from damage as the branches continually rub together when the wind blows through the canopy. This rubbing action results in bark being stripped from the contact area, and makes it necessary for the plant to expend resources on damage repair. Additionally, if crossing branches aren't corrected early on, the branches may fuse together creating a weak spot in the plant that is susceptible to future wind or ice damage.
  3. Remove old wood. Old wood is considered to be wood older than the current season's new growth. Older wood in a plant can often be damaged or generally unproductive from a fruiting or flowering standpoint. Removing older branches or canes can encourage new growth to rejuvenate the appearance of a neglected, older shrub. Furthermore, removing old wood opens the plant up to improved air circulation and light exposure within the plant interior.

Once these three types of pruning cuts have been completed, take a moment to evaluate the plant. It is possible that these pruning tasks have accomplished the pruning goals for the plant.

If further pruning is necessary, remember these guidelines for general pruning.

  • Less is more. Just like getting a haircut, more plant material can be removed, but it's never possible to put it back on once it's been cut off. Remove small amounts of plant material at a time. Then, step back from the plant to evaluate and plan the next cuts.
  • Never remove more than one-third of the plant at one time. Removing more than one-third of the plant can stress the plant beyond its ability to recover and withstand other possible stresses such as insect and disease attack or environmental stresses including drought or extreme cold.
  • Make pruning cuts just above a node or back to either a lateral branch or the main trunk of a plant. A pruning cut just above a node should be at a 45-degree angle, but take care not to leave a stub or damage the node. Pruning back to a lateral branch or the main trunk of a plant makes for a neater appearance, opens the canopy of the plant, and allows the plant to heal wounds more efficiently.

For additional information on pruning trees and shrubs, visit our HGIC fact sheets: HGIC 1053, Pruning Shrubs, and HGIC 1003, Pruning Trees.