Pruning Dos and Don’ts

Southwest Yard & Garden by Dr. Marisa Thompson

Pruning Dos and Don’ts

SCROLL DOWN FOR A LIST OF PRUNING WORKSHOPS ACROSS NEW MEXICO IN 2020!


For tips on WHEN to prune, visit https://nmsudesertblooms.blogspot.com/2020/02/when-to-prune-considerations-galore.html

The partial donut formed on this poorly pruned mulberry tree in Albuquerque is an example of what happens when the branch collar is nicked and cannot form a full donut ring to seal the wound at the surface. Photo credit Judy Nickell .

Example of a good pruning cut on a cork oak in Las Cruces shows that the branch collar was left intact, and a donut-shaped ring has formed at the rim. Unfortunately, this limb was so big the collar has not been able to fully seal the wound from the outside, but the wound was sealed internally. Photo credit M. Thompson.

Question: I get stressed this time of year because I know it is almost time to prune our landscape trees. Can you give some tips on how to prune with confidence?

-          Geri T., Albuquerque

Answer: The task of pruning used to stress me out too. Every winter I’d watch a few YouTube videos, take some deep breaths, and then put pruning off for another time because I felt that my skills weren’t good enough to—cut it.

It is actually good that you are reluctant to jump outside and whack away without an action plan. While some pruning may be necessary for safety and canopy manipulation, any time we cut into a tree we are creating a potential site for infection. One form of chronic tree torture is pruning annually just because.

Recommended pruning techniques have changed—and continue to change—with new research. In 2017, the American National Standards Institute published a revised pruning manual entitled “Tree Care Operations – Tree, Shrub, and Other Woody Plant Management – Standard Practices (Pruning)” or the “ANSI A300.” Keeping up with the newest guidelines translates to better tree care. As the late Dr. Al Shigo, biologist and plant pathologist with the U.S. Forest Service, said, “People who prune the old-fashioned way should be made to go to an old-fashioned dentist.”

Tree wounds never heal. They can seal, but only if cut properly. At the base of each branch, where it meets the trunk, there is a special area called the branch collar (Figure 1, below). Think of the trunk as wearing a short-sleeved shirt with the sleeve bunched up (branch collar) and the branch as the arm extending out of the sleeve. The tissue in the branch collar (bunched sleeve) is capable of sealing a clean-cut pruning wound, but only if the entire branch collar is in place. This means that there will be a bump on the trunk after pruning, but at least it will seal. If a flush cut is made, there will not be enough collar to seal the wound. Often, the branch collar is observable, but even if you can’t see it, you should try to visualize it so that you are sure to leave the branch collar tissues intact. Don’t nick the collar.

Figure 1. Proper pruning principles include finding the branch collar, removing heavy outer limbs (not shown), then making a partial upward cut (A) several inches out from the final cut. Next, make a full downward cut a half-inch farther out (B) to take the weight off. Now you are ready to make the final cut (C-D) without nicking the branch collar. (Image courtesy of the Arbor Day Foundation, www.arborday.org)

The bigger the wound, the harder the tree has to work and the longer it will take to seal it. This is why the best approach is to prune at the time of planting, when the branches and pruning wounds are the smallest. Ideally, you will never have to prune it again. Here are some guidelines for selecting branches to prune at any stage of tree growth:

The ABCDs of pruning (starting with D)

D is for Dead. Dead branches go first. It can be difficult to identify a dead branch in the winter though, but luckily it’s always a good time to prune a dead branch, so when you see one, go ahead and prune it out, regardless of the season.

A is for Apical. Apical dominance pruning involves selecting and promoting a central leader, which is the main stem from the trunk up through the canopy to the top of the tree. Apical just means apex or tip. Most trees are pruned for apical dominance and display the classic A-form tree; you can visually follow the main stem from the lowest branch up to the top of the tree in a relatively straight line as it tapers and supports lateral branches. Some fruit trees, like peaches, generate higher yields when sunlight is encouraged to get into the inner canopy using an “open-center” form instead of the A-form. Another example of a tree that didn’t read the book about correct form might be a beautiful desert willow that has multiple stems starting from a V-shaped trunk.

B is for Bad. Prune out the bad branches that are weak and might pose a hazard if they were to fall. Damaged, diseased, or structurally defective branches may be detrimental to the long-term health and structure of the tree. Take the time to determine if serious pests like cankers or galls are the cause of decay, malformations, or cracks. If infectious diseases are present, you’ll need to keep tools clean so that you are not spreading problems from plant to plant. If you need help identifying a pest, contact the NMSU Plant Diagnostic Clinic (http://aces.nmsu.edu/ces/plantclinic/). In the meantime, disinfect pruning tools between cuts.

C is for Competing. Competing branches grow in ways that impede the growth of other branches, like rubbing, or cause clearance issues, like for pedestrians. These branches may not be competing yet, but if you foresee that you will have to prune one of them eventually, go ahead and take it out now.

Of course, I can’t include all of the pruning rules in this little column. See below for more pruning resources, the best tools, and how to disinfect them. Hint: it ain’t bleach. 

YOU'RE INVITED! Come to our FREE annual Pruning Workshop on Saturday, Feb. 8, 2020 from 9am-12pm at the NMSU Agricultural Science Center at Los Lunas. We’ll offer fruit tree and grapevine pruning demos and hands-on instruction with NMSU Extension Viticulture Specialist Dr. Gill Giese, Albuquerque City Forester Joran Viers, my esteemed predecessor Dr. Curtis Smith, and yours truly. 


Upcoming pruning workshops around the state. I’ll list as many as possible on this page as I hear about them...

Bernalillo County:

• January 18th:

• February 29th - Fruit Tree Pruning with Joran Viers from 9 AM-12 PM. $5, registration required. More info: https://aces.nmsu.edu/county/bernalillo/farmranch/documents/2020-agri-classes--update.pdf

• March 7th - Gutierrez-Hubbell House Backyard Farming Workshop series - Pruning Fruit Trees and Ornamentals with Bernalillo County Extension Horticulture Agent Sara Moran and me (Marisa Thompson) 

• March 14th - Grape pruning, Los Ranchos Agri-Nature Center, with Bernalillo County Extension Agriculture Agent John Garlisch & Dr. Gill Giese

De Baca County:

• February 20 - Tree Care & Pruning Workshop with Marisa Thompson from 9-12 am at the De Baca County Extension Office

Doña Ana County: 

• Pecan Pruning Workshops with Dr. Richard Heerema
• February 20 near Las Cruces, NM
• also February 18 in Eloy, AZ

Quay County: 

• February 19th - Tree pruning workshop in Tucumcari, with Quay County Extension Agent Jason Lamb and me (Marisa Thompson)

Rio Arriba County:

• March 12th - Grape pruning, with Dr. Gill Giese and Rio Arriba County Extension Agent Don Martinez

Sierra County:

• Monday March 9 with Sierra County Extension Agent Sara Marta, Dr. Richard Heerema, and me (Marisa Thompson)

Valencia County:

• Sat Feb 8th:

Sandoval County: 

• Week of February 18th -- Grape pruning at Santa Ana Pueblo vineyard, with Dr. Gill Giese, Daniel Bird, and vineyard manager Jim Peterson

Additional resources:

Pruning Information for Tree Owners from TreesAreGood.org

Disinfecting pruning tools: Use a common household cleaner like Lysol. In studies on pruning tool disinfection, these household cleaners performed as well as bleach, but bleach was the most harmful to blade surfaces.

Tree Pruning Techniques NMSU Guide H-156

Pruning the Home Orchard NMSU Guide H-327

Thinning Fruit for Tree Health

For more gardening information, including decades of archived Southwest Yard & Garden columns, visit the NMSU Extension Horticulture page (http://desertblooms.nmsu.edu/), follow us on social media (@NMDesertBlooms), or contact your County Extension office (https://aces.nmsu.edu/county).

Marisa Thompson, PhD, is the Extension Horticulture Specialist for New Mexico State University and is based at the Agricultural Science Center at Los Lunas.