Avoiding Pruning Pitfalls

This article serves as a foundation regarding pruning woody landscape trees and shrubs. As with all pruning, there is nuisance depending on the particular goals, and plant material. Certainly with pruning there are scientific techniques and principles to keep in mind, while also keeping in mind the art component of pruning that can be hard to explain and comes with experience and practice. My hope is that you learn some important principles to keep in mind with all pruning, and avoid some common mistakes. As always, reach out to your local Cooperative Extension office for further guidance on pruning based on your particular situation if you have further questions. 

Timing of Pruning

One of the critical pieces of information needed to prune correctly is knowing the proper timing of when it is best to prune. Generally, the ideal time to prune plants is when they are dormant. This reduces shock, and enables the plant to heal itself more efficiently. There are exceptions to this rule though, namely the first question that must be asked is what plant material are you pruning?

Woody Flowering Plants: Old Wood vs. New Wood

Most woody flowering plants can be classified into two primary groups. The first group blooms and sets flower buds primarily on the previous year’s growth. This is called blooming on “old wood” or stems and vegetative material that was created the previous year. Generally this group blooms in the fall, or early spring. The second group of flowering plants in the landscape bloom primarily on current year’s growth or in other words, the current year’s vegetative/stem structures. Generally this group blooms from late spring through fall. Why does this matter? Well, if pruned at the wrong time, flowers can easily be cut off for the year resulting in no flowers for an entire year!

Examples of “old wood” blooming plants include bigleaf hydrangea (Hydrangea macrophylla), which bloom primarily in the summer. Pruning should be completed on this plant prior to the fall, ideally right after blooming to ensure that future flower buds that are borne in the fall of the year on stems are not impacted. Pruning in the fall could result in Hydrangea macrophylla not blooming the following year due to the removal of flower buds on older growth. Other examples of “old wood” plants include forsythia, oakleaf hydrangea, some varieties of azaleas (traditional spring blooming varieties bloom on old wood unlike Encore azaleas and other cultivars that bloom on old and new wood alike).

Types of “new wood” blooming plants include panicle hydrangea (Hydrangea paniculata) which blooms exclusively on new wood that is formed in the spring. These plants can generally withstand pruning in the fall or winter of the year because that wood would not be the current year’s growth, or newly created stem/flower bud tissue. The best time of year to prune would be after blooming which would be fall or winter time. Pruning in the early spring could result in the removal of current year’s growth and the loss of flowering for that season. Other examples of “new wood plants” include rose-of-sharon, crape myrtles, and abelia just to name a few.

If you are curious about bloom timing for your particular plant, utilize the NCSU Extension Gardner Plant Toolbox to learn more.

Other timing considerations…

It is critically important to not prune too early in the plant’s cycle if regular maintenance cuts are being made. Cutting too early in the growing season or even at the later parts of the fall season can spur new branch development that could be damaged by winter weather. Typically in the mountains of WNC, dormant season pruning should be made starting in January or February after warm weather declines and well before spring begins in late March.

Types of Pruning

Regenerative pruning– pruning that is done to cut old wood to within a couple inches of the ground. This is done to encourage cane, or stem development which in turn can increase flowering/fruiting. Blueberries, edgeworthia, and azalea are just some examples of plants where this practice is commonly done. Be sure to rejuvenate plants only when they are older and are well-established.

Regenerative pruning on Knockout Rose.
Photo credit: General Pruning Techniques Factsheet- B. Fair

Heading back (shearing)– reduces length of stem or branch without regard to position or presence of lateral branch. This cut is typically made of shrubbery like boxwoods, hollies, arborvitae that can tolerate shearing to encourage canopy density through lateral bud stimulation. 

Heading back or shearing of a yew shrub.
Photo credit: General Pruning Techniques Factsheet- B. Fair

Thinning/Reduction– thinning cuts that reduce the length of the branch back to a lateral branch of equal or smaller size. These cuts are typically done to reduce canopy density for various reasons. This can help with structural balance within trees (especially fruiting/flowering trees) as well as increasing air circulation within the canopy itself.

Thinning/reduction cuts shown on an arborvitae.
Photo credit: General Pruning Techniques Factsheets- B. Fair

Removal of dead/diseased wood– this is done exactly like it sounds…removing deadwood from a tree is a relatively straightforward type of pruning that can be done year-round. It can be important to remove deadwood for renewing canopy density of trees and shrubs and revitalizing overall growth. Be sure to keep the branch collar intact with any removal cuts made! This is how the tree/shrub can heal itself properly after the cut is made. Removing deadwood can also be part of culturally preventing diseases and pests from establishing themselves on the plants you are trying to protect.

Pruning diseased or dead wood at the proper branch angle (red) without impacting bark ridge (yellow).
Photo credit: General Pruning Techniques Factsheet- B. Fair

Techniques of Pruning

3-cut method

When cutting things below 1” in diameter, one can cut fairly easily with just a single cut. However, on larger limbs it could be warranted to practice what is called the 3-cut method of pruning. In this process, one first makes an undercut 3-4” above where the desired cut will be made. A second cut is done from the top of the limb 5-6” from where the final cut will be made. The last cut is the final cut which should be around 45 degrees when completed with the goal of not leaving a stub, but also not cutting into the branch collar to allow for healing.

To Paint or Not to Paint…DON’T

Wound painting is an antiquated and outdated practice that creates more problems and does not heal pruning cuts at all. In fact wounding paints/wax products can trap moisture thereby resulting in rot, and can inhibit natural compartmentalization and healing. There is no scientific evidence that suggests that it helps a plant by adding wound paint, latex or wax products to close over a pruning wound. Certain fungicide products can be added to pruning surfaces to aide in healing and prevent disease establishment in certain situations but for the most part are not necessary. 

Tools of Pruning

Bypass handshears– designed to cut small branches up to about ½” diameter; passes a curved blade past an anvil.

Anvil handshears– designed to cut small branches up to about ½” diameter; has a straight blade sharpening on both sides that cuts against a flat anvil blade. Generally less common and tends to pinch cambial tissue making it less desirable to use when compared to bypass blades.

Bypass/anvil lopers- (see above for differences between anvil and bypass); used to prune branches up to 1” in diameter.

Bypass/anvil shears– (see above for differences between anvil and bypass); used to cut multiple small branches with a singular cut rather than having to cut one small branch at a time using handshears.

Handsaw– used to prune branches ½” or larger (can be used to cut larger branches); can also use pole saw which is a handsaw with a 6’ or longer extension used for cutting in tree canopies.

Chainsaw– used to prune branches larger than ½”; must use appropriate PPE and have appropriate training to be able to properly use this tool.

Importance of Sterilization

Sterilizing equipment is critically important to prevent the spread of pathogens in between different specimens and branches. Vascular pathogens can be transmitted on pruning equipment in between job sites or specimens in the landscape which can exacerbate disease issues. Sterilization can be done using one part bleach/isopropyl alcohol to 9 parts water (this can corrode tools over time however if not properly oiled) or more commonly, cleaning agents like Lysol or Pine Sol can be used effectively to sterilize equipment with no concern of corrosion. 

My hope is that this gives you some guidance as a launching point in the area of pruning woody landscape plants. This is by no means an exhaustive guide to pruning best management practices. If you are interested in reading more material or other resources, see the links below. Reach out to your local Cooperative Extension office for questions related to pruning and we’d be happy to assist. 

Resources:

NCSU Extension- General Pruning Techniques Factsheet

NCSU Extension- How to Prune Specific Plants Factsheet

NCSU Guilford Co. Extension- Proper Pruning -Resource Links Factsheet