Frequently Asked Questions

Mature Tree Care

The PHC alternative

Maintaining mature landscapes is a complicated undertaking. You may wish to consider a professional Plant Health Care (PHC) maintenance program, which is now available from many landscape care companies. Their program is designed to maintain plant vigor and should initially include inspections to detect and treat any existing problems which could be damaging or fatal. Thereafter, regular inspections and preventive maintenance will assure plant growth and beauty. Refer to our “Plant Health Care” brochure for more information.

This brochure is one in a series published by the International Society of Arboriculture as a part of its Consumer Information Program. You may have additional interest in the following titles currently in the series:

  • Avoiding Tree Damage During Construction
  • Avoiding Tree and Utility Conflicts
  • Benefits of Trees
  • Buying High-Quality Trees
  • Insect and Disease Problems
  • Mature Tree Care
  • New Tree Planting
  • Plant Health Care
  • Proper Mulching Techniques
  • Pruning Young Trees
  • Pruning Mature Trees
  • Recognizing Tree Hazards
  • Treatment of Trees Damaged by Construction
  • Tree Selection
  • Tree Values
  • Trees and Turf
  • Why Hire an Arborist?
  • Why Topping Hurts Trees

Although tree removal is a last resort, there are circumstances when it is necessary. An arborist can help decide whether or not a tree should be removed. Professionally trained arborists have the skills and equipment to safely and efficiently remove trees. Removal is recommended when a tree:

  • is dead, dying, or considered irreparably hazardous
  • is causing an obstruction, or is crowding and causing harm to other trees and the situation 
    is impossible to correct through pruning.
  • is to be replaced by a more suitable specimen
  • should be removed to allow for construction

With proper maintenance, trees are attractive and can add considerable value to your property. Poorly maintained trees, on the other hand, can be a significant liability. Pruning or removing trees, especially large trees, can be dangerous work. It should only be performed by those trained and equipped to work safely in trees. For more information on mature tree care, contact your local ISA Certified Arborist, garden center, county extension agent, or city arborist.


Pruning is the most common tree maintenance procedure next to watering. Pruning is often desirable or necessary to remove dead, diseased, or insect infested branches, improve tree structure, enhance vigor, or maintain safety. Since each cut has the potential to change the growth of (or cause damage to) a tree, no branch should be removed without a reason. Removing foliage from a tree has two distinct effects on its growth. 

Removing leaves reduces photosynthesis and may reduce overall growth. This is why pruning should always be preformed sparingly. Over-pruning is extremely harmful because without enough leaves, a tree cannot gather and process enough sunlight to survive. However, after pruning, the growth that does occur takes place on fewer shoots, so they tend to grow longer than they would without pruning. Understanding how the tree responds to pruning should assist you when selecting branches for removal. 

Pruning mature trees may require special equipment, training, and experience. If the pruning work requires climbing, the use of a chan or hand saw, or the removal of large limbs, the use of personal safety equipment, such as protective eye wear and hearing protection, is a must. Arborists can provide a variety of services to assist in performing the job safely and reducing risk of personal injury and damage to your property. They also are able to determine what type of pruning is necessary to maintain or improve the health, appearance, and safety of your trees.


Fertilization is another important aspect of mature tree care. Trees require certain nutrients (essential elements) to function and grow. Urban landscape trees are often growing in soils that do not contain sufficient available nutrients for satisfactory growth and development. In these situations it may be necessary to improve plant vigor. 

Fertilizing a tree can increase growth, reduce susceptibility to certain diseases and pests, and can even help reverse declining health. However, if fertilizer is not applied wisely, it may not benefit the tree at all, and may even adversely affect the tree. Mature trees making satisfactory growth may not require fertilization. When considering supplemental fertilizer, it is important to know what nutrients are needed, and when and how it should be applied. 

Soil conditions, especially pH and organic matter content, vary greatly making the proper selection and use of fertilizer a somewhat complex process. When dealing with a mature tree that provides considerable benefit and value to your landscape, it is worth the time and investment to have the soil tested for nutrient content. Most quality garden centers can arrange to have your soil tested at a soil testing laboratory. With the test results in hand, you can consult your local garden center staff, ISA Certified Arborist, or a plant care professional for advice on application rates, timing, and the best blend of fertilizer for each of your trees and other landscape plants. 

Mature trees have expansive root systems that extend from two to three times the size of the leaf canopy. A major portion of actively growing roots are located outside the tree’s dip line. It is important to understand this when applying fertilizer to your trees as well as your turf. Many lawn fertilizers contain weed and feed formulations that may be harmful to your trees. When you apply a broadleaf herbicide to your turf, remember, tree roots co-exist with turf roots. The same herbicide that kills broadleaf weeds in your lawn is picked up by tree roots and can harm or kill your broadleaf trees if applied incorrectly. understanding the actual size and extent of a tree’s root system, before you fertilize, is necessary to determine how much, what type, and where to best apply fertilizer.


Mulching can reduce environmental stress by providing tress with a stable root environment that is cooler and contains more moisture than the surrounding soil. Mulch can also prevent mechanical damage by keeping machines such as lawnmowers and weedwhips away from the tree’s base. Further, mulch reduces competition from surrounding weeds and turf.

To be most effective in all of these functions, mulch should be placed two to four inches deep and cover the entire root system, which may be as far as two or three times the diameter of the branch spread of the tree. If the area and activities happening around the tree do not permit the entire area to be mulched, it is recommended that you mulch as much of the area as under the drip line of the tree as possible (refer to diagram). When placing mulch, care should be taken not to cover the actual trunk of the tree. This mulch-free area, one to two inches wide at it’s base, is sufficient to avoid moist bark conditions and prevent trunk decay.

An organic mulch layer of two to four inches of loosely shredded leaves, pine straw, peat moss, or composted wood chips is adequate. Plastic should not be used because it interferes with the exchange of gases between soil and air, which inhibits root growth. Thicker mulch layers, five to six inches or greater, may also inhibit gas exchange.

Tree Inspection

Tree inspection is an evaluation tool to call attention to any change in the tree’s health, before the problem becomes too serious. By providing regular inspections of mature trees (at least once a year), you can prevent or reduce the severity of future disease, insect, and environmental problems. During the inspection, be sure to examine four characteristics of tree vigor: new leaves or buds, leaf size, twig growth, and crown dieback (gradual death of the upper part of the tree).

A reduction in extension of shoots (new growing parts), such as buds or new leaves, is a fairly reliable cue that the tree’s health has recently changed. To evaluate this, compare the growth of the shoots over the past three years. Determine if there is a reduction in the tree’s typical growth pattern. 

Further signs of poor tree health are trunk decay and/or drown dieback. These symptoms often indicate problems that began several years before. Loose bark or deformed growths, such as trunk conks (mushrooms) are common signs of stem decay. 

Any abnormalities found during these inspections, including insect activity, spotted, deformed, discolored or dead leaves and twigs, should be noted and watched closely. If you are uncertain as to what should be done, report your findings to your local ISA Certified Arborist, or other tree care professional, for advice on possible treatment.

Treatment of Trees Damaged by Construction

For Additional Information

This brochure is one in a series published by the International Society of Arboriculture as a part of its Consumer Information Program. You may have additional interest in the following titles currently in the series:

  • Avoiding Tree Damage During Construction
  • Avoiding Tree and Utility Conflicts
  • Benefits of Trees
  • Buying High-Quality Trees
  • Insect and Disease Problems
  • Mature Tree Care
  • New Tree Planting
  • Plant Health Care
  • Proper Mulching Techniques
  • Pruning Young Trees
  • Pruning Mature Trees
  • Recognizing Tree Hazards
  • Treatment of Trees Damaged by Construction
  • Tree Selection
  • Tree Values
  • Trees and Turf
  • Why Hire an Arborist?
  • Why Topping Hurts Trees
Monitoring for Decline and Hazards

Despite your best efforts you may lose some trees from construction damage. Symptoms of decline include smaller and fewer leaves, dieback in the crown of the tree, and premature fall color. If a tree dies as a result of root damage, it may be an immediate hazard and should be removed right away. Examine your trees for signs of possible hazards. Look for cracks in the trunk, split or broken branches, and dead limbs. Watch for indications of internal decay such as cavities, carpenter ants, soft wood, and mushroom-like structures growing on the trunk, root crown, or along the major roots. If you detect and defects or suspect decay, consult and arborist for a professional assessment. It is prudent to have your trees evaluated periodically by a professional.

You should also inspect your trees for signs of insects or diseases. Stressed trees are more prone to attack by certain pests. Talk to your arborist about putting your trees on a program of Plant Health Care (PHC). This may help identify and treat problems before they become a threat to the life of your trees.

What about Fertilization?

Most experts recommend that you do not fertilize your trees the first year after construction damage. Water and mineral uptake may be reduced due to root damage. Excessive soil salts can draw water out of the roots and into the soil. In addition, nitrogen fertilization may stimulate top growth at the expense of root growth. It is a common misconception that applying fertilizer gives a stressed tree a much needed shot in the arm. Fertilization should be based on the nutritional needs of the trees on a site. Soils can be analyzed to determine whether any of the essential minerals are deficient. If soil nutrients are deficient, supplemental fertilization may be indicated. It is advisable to keep application rates low, however, until the root system has had time to adjust.

Improving Aeration of the Root Zone

Drilling Holes/Vertical Mulching Compaction of the soil and increase in grade both have the effect of depleting the oxygen supply to tree roots. If soil aeration can be improved, root growth and water uptake can be enhanced. The most common method of aeration of the root zone involves drilling holes in the ground. Holes are usually 2-4 inches in diameter and are made about 3 feet on center, throughout the root zone of the tree. The depth should be at least 12 inches, but may need to be deeper if the soil grade has been raised. Sometimes the holes are filled with peat moss, wood chips, pea gravel, or other material that maintain aeration and support root growth. This is called vertical mulching.

Radial Aeration More recent research has shown promising results with another method of aeration called radial aeration. Narrow trenches are dug in a radial pattern throughout the root zone. These trenches appear similar to the spokes of a wagon wheel. It is important to begin the trenches 4-8 feet from the trunk of the tree to avoid cutting any major support roots. The trenches should extend at least as far as the drop line of the tree. If the primary goal is to reduce compaction, the trenches should be about 1 foot in depth. They may need to be deeper if the soil grade has been raised. This technique is appropriate for isolated trees, where the roots of other trees would not be damaged.

The narrow trenches can be backfilled with the topsoil or compost. Root growth will be greater in the trenched area than the surrounding soil. This can give the tree the added boost it needs to adapt to the compacted soil or new grade.

Vertical mulching and radial trenching are techniques that may improve conditions for root growth. If construction damaged trees are to survive the injuries and stresses they have suffered, they must replace the roots that have been lost.


One of the simplest and least expensive things you can do for your trees may also be one of the most effective. Applying a three to four inch layer of an organic mulch such as wood chips, shredded bark, or pine needles over the root system of a tree can enhance root growth. The mulch helps condition the soil, moderates soil temperatures, maintains moisture, and reduces competition from weeds and grass. The mulch should extend as far out from the tree as practical for the landscape site. (If the tree had to say, the entire root system would be mulched.) Note: Do not apply the mulch any deeper than four inches, and do not pile it against the trunk.

Irrigation and Drainage

One of the most important tree maintenance procedures following construction damage is to maintain an adequate, but not excessive supply of water to the root zone. If there is a drainage problem the trees will decline rapidly. This must be corrected if the trees are to be saved, If soil drainage is good, be sure to keep the trees well watered especially during the dry, summer months. A long, slow soak over the entire root zone is the preferred method of watering. Keep the top 12 inches moist, but avoid over-watering. Avoid frequent, shallow waterings. Make sure surface water drains away from the tree. Proper irrigation may do more to help the trees recover from construction stress than anything else you could do.

Treating Trunk and Crown Injuries

Pruning Branches that are split, torn, or broken should be removed. Also, remove any dead, diseased, or rubbing limbs from the crowns of trees. Sometimes it is necessary to remove some lower limbs to raise the canopy of a tree and provide clearance below. It is best to postpone other maintenance pruning for a few years.

Old recommendations suggest that the tree canopies should be thinned or topped to compensate for root loss. There is no conclusive research to support this practice. Thinning the crown can reduce the trees’ food-making capability and may stress the tree further. It is better to limit pruning in the first few years to hazard reduction and removal of deadwood. Do not top the trees.

Cabling and Bracing Trees growing in wooded areas are usually not a threat to people or structures. Trees that are close to houses or other buildings must be maintained to keep them structurally sound. If branches or tree trunks need additional support, a professional arborist may be able to install cables or bracing rods. If cables or braces are installed however, they must be inspected regularly. The amount of added security offered by the installation of support hardware is limited. Not all weak limbs are candidates for these measures.

Repairing Damaged Bark and Trunk Wounds Often the bark may be damaged along the trunk or major limbs. If this happens, remove the loose bark. Jagged edges can be cut away with a sharp knife. Take care not to cut into living tissue.

Wound Dressings Wound dressings were once thought to accelerate wound closure, protect against insects and diseases, and reduce decay. However, research has shown that dressings generally do not reduce decay or speed closure, and rarely prevent insect or disease infections. Most experts recommend that wound dressings not be used. If a dressing must be used for cosmetic purposes, use just a thin coating of non-toxic material.

Inspection and Assessment

Since construction damage can affect the structure and stability of a tree, your arborist should check for potential hazards. This may involve a simple visual inspection, or instruments may be used to check for the presence of decay. Sometimes the hazard can be reduced or eliminated by removing an unsafe limb, pruning to reduce weight or installing cables or braces to provide structural support. An often-overlooked method of reducing hazards is to move objects could be hit, or to limit access to the hazardous area. If there is doubt about the structural integrity of a tree or the hazard cannot be adequately reduced, it should be removed. Although the goal is to preserve the trees whenever possible, that goal must not supersede any question of safety.

Damage caused by construction
  • Physical injury to the trunk and crown
  • Soil compaction in the root zone
  • Severing of roots
  • Smothering roots by adding soil
  • Split and broken branches
  • New exposure to wind and sunlight

Why Topping Hurts Trees

Hiring an Arborist

Pruning large trees can be dangerous. If pruning involves working above the ground or using power equipment, it is best to hire a professional arborist. An arborist can determine what type of pruning is necessary to improve the health, appearance, and safety of your trees. A professional arborist can provide the services of a trained crew, with all of the required safety equipment and liability insurance.

There are a variety of things to consider when selecting an arborist:

  • Membership in professional organizations, such as the International Society of Arboriculture (ISA), the National Arborist Association (NAA, or the American Society of Consulting Arborists (ASCA)
  • Certification through the ISA Certified Arborist program
  • Proof of insurance
  • A list of references (Don’t hesitate to check)
  • Avoid using the services of any tree company that:
    • Advertises topping as a service provided. Knowledgeable arborists know that topping is harmful to trees and is not an accepted practice.
    • Uses tree climbing spikes to climb trees that are being pruned. Climbing spikes can damage trees, and their use should be limited to trees that are being removed.
Alternatives to Topping

There are times when a tree must be reduced in height or spread. Providing clearance for utility lines is an example. There are recommended techniques for doing this. Is practical, branches should be removed back to their point of origin. If a branch must be shortened, it should be cut back to a lateral that is large enough to assume the terminal role A rule of thumb for this is to cut back to a lateral that is at least 1/3 the diameter of the limb being removed.

This method of branch reduction helps to preserve the natural form of the tree. However if large cuts are involved, the tree may not be able to close over and compartmentalize the wounds. Sometimes the best solution is to remove the tree and replace it with a species that is more appropriate for the site.

Topping Is Expensive

The cost of topping a tree is not limited to what the perpetrator is paid. If the tree survives, it will require pruning again within a few years. It will either need to be reduced again, or storm damage will have to be cleaned up. If the tree dies it will have to be removed. Topping is a high maintenance pruning practice.

There are some hidden costs to topping. One is the reduction in property value. Healthy, well maintained trees can add 10-20% to the value of a property. Disfigured topped trees are considered and impending expense.

Another potential cost of topped trees is the potential liability. Topped trees are prone to breaking and can be hazardous. Since topping is considered to be an unacceptable pruning practice, any damage caused by branch failure of a topped tree may lead to finding of negligence in a court of law.

Topping Makes Trees Ugly

The natural branching structure of a tree is a biological wonder. Trees form a variety of shapes and growth habits, all with the same goal of presenting their leaves to the sun. Topping removes the ends of the branches, often leaving ugly stubs. Topping destroys the natural form of a tree.

Without the leaves (up to six months of the year in temperate climates) a topped tree appears disfigured and mutilated. With the leaves, it is a dense ball of foliage, lacking its simple grace. A tree that has been topped can never fully regain its natural form.

Topping Creates Hazards

The survival mechanism that causes a tree to produce multiple shoots below each topping cut comes at great expense to the tree. These shoots develop from buds near the surface of the old branches. Unlike normal branches that develop in a “socket” of overlapping wood tissues, these new shoots are only anchored in the outermost layers of the parent branches.

The new shoots grow very quickly, as much as 20 feet in one year in some species. Unfortunately, the shoots are very prone to breaking, especially during windy conditions. The irony is that while the goal was to reduce the tree’s height to make it safer, it has been made more hazardous than before.

Topping Can Lead to Sunburn

Branches within a tree’s crown produce thousands of leaves to absorb sunlight. when the leaves are removed, the remaining branches and trunk are suddenly exposed to high levels of light and heat. The result may be sunburn of the tissues beneath the bark. This can lead to cankers, bark splitting, and death of some branches.

Topping Causes Decay

The preferred location to make a pruning cut is just beyond the branch collar at the branch’s point of attachment. The tree is biologically equipped to close such a wound provided the tree is healthy enough and the wound is not too large. Cuts made along a limb, between lateral branches, create stubs with wounds that the tree may not be able to close. The exposed wood tissues will begin to decay. Normally a tree will “wall off” or compartmentalize the decaying tissues. But few trees can defend the multiple severe wounds caused by topping. The decay organisms are given a free path to move down the branches.

Topping Stresses Trees

Topping often removes 50-500% of the leaf bearing crown of a tree. Since the leaves are the “food factories” of a tree, this can temporarily “starve” a tree. The severity of pruning triggers a sort of survival mechanism. The tree activates latent buds, forcing the rapid growth of multiple shoots below each cut. The tree needs to put out a new crop of leaves as soon as possible. If a tree does not have the stored energy reserves to do this, it will be seriously weakened and may die.

A stressed tree is more vulnerable to disease infestations. Large, open pruning wounds expose the sapwood and heartwood to attack. The tree may lack sufficient energy to chemically “defend” the wounds against invasion. Some insects are actually attracted to stressed trees by chemical signals.

What is Topping

Topping is the indiscriminate cutting back of tree branches to stubs or lateral branches that are not large enough to assume the terminal role. Other names for topping include “heading”, “tipping”, “hat-racking”, and “rounding over”.

The most common reason given for topping is to reduce the size of a tree. Often homeowners feel that their trees have become too large for their property. people fear that tall trees may pose a hazard. Topping, however, is not a viable method for height reduction, and certainly does not reduce the hazard. In fact, topping will make a tree more hazardous in the long term.

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