Pruning Trees | Why Prune Trees | Staking/Tree Protection/Guards | Watering | Mulching Trees

Pruning Trees

Need to know the who, what, when, where, why, and sometimes how of pruning?  Click here to tap into an excellent publication from the USDA Forest Service covering all the essential pruning basics, such as

  • why prune
  • how to prune
  • what season is best for pruning
  • pruning for shape
  • pruning for growth
  • when to call a professional
  • what to look for when calling a professional

(Pub NA-FR-01-95).

For more information on topics that range from why you should hire an arborist for tree repair, to pruning young trees, to pruning mature trees, click here: and here:


Why do we prune trees?

Trees in a “natural” forest are seldom pruned and they do fine.  On the other hand, people in urban areas insist on pruning trees frequently…

Photo Dave Hanson:
Bur Oak – Pruning to correct bad decisions.

Are urbanites simply “control freaks” with a need to control some living thing?  Not exactly, there are valid reasons (safety, health of the tree, and aesthetics) to get out there and take a good look at the structure and condition of the trees in our landscape.  Trees in the natural forest for example tend to randomly drop limbs (natural pruning) and fall over unpredictably during storm events or from internal decay.

Increased potential for property damage and personal injury in the urban forest dictates that limb dropping and trees falling over should be predicted and controlled, as much as possible.  Any tree may develop structural problems or become damaged and become a risk.  So, developing a regular inspection and pruning cycle for landscape trees is highly recommended to help eliminate some of the “risk.”

Arborists are trained to identify those “risks” in trees and can make recommendations to eliminate or reduce the risk to an acceptable level.  Reducing the risk can often be accomplished without removing the tree by utilizing one of the following approaches:

Three basic approaches to pruning:

From the United States Forest Service brochure “How To Prune Trees” (Bedker et al.):

1) Crown reduction:A method to reduce the overall height of a tree.

Photo Chad Giblin:
Crown Reduction for power line clearance

Crown reduction is most commonly used to alleviate power line conflicts.  According to a flyer from Connexus energy (Spring 2004) – “Trees are the number one cause of power outages.”

This approach may also be employed to clear site lines for a scenic overlook or vista.

Crown reduction or drop-crotch pruning should only be considered as a last resort treatment because it opens multiple large and small wounds on a tree and those wounds can be entry points for insects or disease…

2) Crown thinning / cleaning:This technique is often used to open up the canopy for air movement through the tree and to provide light penetration to the understory.  Beyond that, this pruning approach considers many things:  correction of structural problems such as: tight branch angles, included bark, crossing branches, broken or split tree parts…

Correcting structural problems can prevent overloading problems from wind, ice, or snow or simply the weight of a maturing limb.

Photo by Josh Plunkett:  Co-dominant stem split out under a snow load.  A predictable and preventable problem.

Crown cleaning also consists of removing deadwood, hangers (broken branches) as well as removal of diseased wood or insect infestations.

Deadwood and hangers (lodged, detached branches) present a risk to people, cars, houses and other objects (targets) below.  Also, by removing signs of disease and / or insect infestations a serious problem for the tree may be stopped before it progresses to a full-blown disorder.  Maintenance and correction of storm damage fall into this category.

3) Crown raising:Simply put, this is the removal of lower branches to improve site lines near roads and to allow for movement of people and equipment under trees.  Along city streets for example, many municipalities remove permanent tree branches to a minimum height of 16 feet from the ground or street surface.


Garbage trucks and other big rigs will prune the limbs by tearing them from the tree often causing irreparable damage to the main stem.

Photos Dave Hanson: This ruptured stem was caused by a delivery truck hitting the low hanging branch on the right.

Along sidewalks, permanent tree branches should be a minimum of 8 feet above the sidewalk to allow for pedestrian traffic and snow removal equipment.

Depending where a tree is located in the landscape determines if branches are raised or allowed to sweep to the ground.

Low hanging tree branches restrict movement and present poking and head-banging hazards in our yards and parks.  So, in some instances the tree branches should be raised to allow people and equipment to move underneath.

Putting this into Practice:

If you are responsible for a landscape that contains trees – there is some pruning in your future…or there should be!

What or Who is an arborist?For more information visit

Hold on, before you grab the chainsaw, consider taking a brief course on pruning or at least read some of the current research on pruning trees.  Unfortunately, there are still a lot of incorrect pruning practices taking place – bad pruning cuts, pruning practices that permanently damage trees and pruning performed during the wrong season for the tree.

Flush cutting:

There is a three cut method to pruning:

  • Cut number 1 is an undercut of the branch to prevent the bark and wood fibers tearing down the main stem. 
  • Cut number 2 simply removes the weight of the branch outside of cut number 1. 
  • The third and final cut removes the branch stub near, but outside of the branch collar.

The final pruning cut should take into consideration the branch bark ridge and the branch collar.  Simplistically, the branch collar is a zone of fast growth and within this zone there are several protection mechanisms that protect the trunk of the tree from decay organisms that may enter the branch.  By leaving the branch collar intact – the main trunk of the tree will be better protected from decay processes…

Photos Courtesy of Gary Johnson
Above: Branch Collar – note the swelling of branch material
Below: Left is the proper cut at the branch collar.  Right is the incorrect large flush cut.

Do not make a cut that is “flush and parallel to the main trunk” because it will leave a large oval wound in the trunk tissue that a tree will have a difficult time sealing over with callus material.  Protection zones and mechanisms are compromised and the tree is more likely to decay.

Topping and Tipping:

There are still companies topping trees and tipping branches on trees.  There are still homeowners requesting that trees be topped and that branches be tipped.  Both topping and tipping are harmful to trees…

Topping and tipping are pruning cuts made indiscriminately on limbs with no regard for placing the cuts near protection zones.  These cuts almost always result in rapid decay of the remaining portion of the limb, while at the same time stimulating large amounts of new growth in the form of epicormic branches also known as water sprouts.  The new growth is typically poorly attached and begins to add considerable weight to a limb or branch being weakened by decay.

Photo Courtesy of Patrick Weicherding:
Tree was topped to improve view of storefront signs

When to Prune:

Don’t prune in April, May and June!
This the time of year when trees deplete their energy reserves and put most of it into new leaves.  Pruning at this time places the energy that has been moved into branches, twigs and leaves onto the burn pile or into a landfill.  This practice places the tree in a stressed state, with an energy deficit that may not be completely recovered in that season.

This is an active time of year for many disease and fungal pathogens (Oak wilt for example).  The warm spring months of April, May, and June typically bring high humidity from spring rains and these factors provide an ideal environment for diseases to flourish. 

Don’t prune in late autumn into early winter
Pruning in late autumn and early winter can lead to winter injury.  The pruning wounds may not have time to “harden off” or prepare for winter.  This can lead to deeper freezing in the tissues around the wound and in essence a larger wound can be created that the tree will have difficulty dealing with.

Summer months and late winter or dormant season is the “best” time to prune.
During the late winter months (February and March), harmful pathogens are at a minimum, mostly inactive; therefore, this is a safe pruning environment from that standpoint.  During this season, deciduous trees have hardened off and when the growing season begins the wounds will be sealed and the callusing process will begin.

Stay away from power lines!
They’re dangerous.

Hire a Professional Arborist:

Tree care can be dangerous and it requires professional knowledge and skill.  The benefits that come from healthy and well cared for trees are worth the investment.

Some basic guidelines:
If the job requires a ladder, a consultation with an arborist may be in order.  Why?

By working from a ladder with a hand saw, chainsaw or even a pole pruner much of the necessary pruning cannot be accomplished and often the tree will end up be “lion’s tailed.”  Lion’s-tailing leaves a tree with a reduced canopy, thus reducing its ability to photosynthesize.  Arborists on the other hand will enter the tree with climbing gear (rope and saddle – NOT SPIKES) and or use a boom truck with a bucket to reach the treetop and branch ends.

If you think the job requires a chainsaw, consulting an arborist is recommended.  Why?

Chainsaws are tools for trained, experienced hands.  Untrained operators often do more harm than good to both the tree and the operator.  Most of the pruning that a tree needs can and should be accomplished with a “hand” pruner or pruning saw.

Exception:  Yes, commercial / municipal arborists and tree-workers are trained in the use of chainsaws and will use chainsaws to complete a portion of their work.  However, note that they also carry handsaws and use them appropriately.

If you have storm-damaged trees, consult an arborist and the tree may be able to stay in the landscape, safely for years to come.  Why? 

Arborists are trained to understand the structure of a tree and to understand how a damaged tree will respond to treatment and more importantly and arborist can answer the question – “Can this tree safely remain in the landscape?”

If you are planning a landscape, please consult an arborist or a landscape designer.

It is important to select the right trees for your locations.  Putting the right trees in the right places can dramatically reduce the costs of pruning and maintenance in your landscape.

The bottom line is that feeling the need to prune trees does not make urbanites “control freaks”; rather, living in geographically condensed spaces in close proximity to mature trees renders us and our belongings potential targets to falling tree parts.  Thus, out of necessity we need to care for our trees not only so that they are pleasing to look at, but so that they remain healthy, safe features in our landscape.



Dave Hanson
Research Specialist, Urban and Community Forestry
Department of Forest Resources
College of Natural Resources
University of Minnesota

Works Cited:
Bedker, Peter J., O’Brien, Joseph G., Mielke, Manfred E., How To Prune Trees.  United States Department of Agriculture, Forest Service Publication NA


Staking/Tree Protection/Guards

There are many reasons why trees are staked, and just as many why they are NOT staked. In fact, staking is not always needed and should not be a part of every planting project. To find out if you need to stake your tree and to learn how to do it correctly, visit:

Tree Wraps and Guards
Tree wraps and guards serve two basic functions: stem protection from physical damage, and modification of the stem’s environment. If materials for protection or modification are used, it’s necessary to install these materials correctly. To help you choose which materials are the right ones to use and how to use them correctly, visit: or



Needless to say, watering is one of the most important things you can do for your tree or landscape. Plant type and soil type are the two most important factors when determining how much to water and how often to water. For in-depth information on watering your trees and plants, try the following links:


Mulching Trees

Mulching is done for a couple of basic reasons; primarily to prevent loss of moisture and to control weeds. Mulch is a layer of organic or inorganic material placed over the root zone of a plant to benefit the roots and the soil. A good guide to mulching, which includes information about mulch application, mulching for weed control, mulching for winter protection, mulching for moisture control, and a list of organic mulches and synthetic mulches can be found at:

For information about mulch, such as “Why mulch?” “How to mulch,” “What kind of mulch to use,” “Where to get mulch,” and why you do NOT want to have a mulch volcano, check out this site:
















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