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Proper Selection and Planting: The first and possibly most important steps in injury prevention are proper selection, placement, and planting of a new tree. Select trees with well-developed crowns and no wounds on the trunk or branches. Trees pruned heavily in the nursery or severely wounded in handling may have serious problems later. Trees should be planted in shallow, wide holes to allow rapid root growth after planting. Planting trees too deep is a common problem. Look at the site carefully and completely. Is the space large enough to accommodate the mature tree's crown and roots? Mulching: Mulching is an important maintenance practice for trees. However, an epidemic of over-mulching is plaguing many managed landscapes. Properly applied mulch increases growth rates, prevents basal damage, and conserves soil moisture. Organic mulch such as wood chips or bark should be applied around the tree to a depth of two to four inches. Mulch should be spread a foot or more from the base of the tree in all directions, but never to a depth of more than two to four inches. Mulch can be placed directly on grass when mulching established trees. Monitor mulched areas during the winter to detect any rodent activity. Mulch should be renewed as needed to keep a constant layer around the tree. Avoid using rocks or plastic sheeting to protect the tree--rocks cause soil compaction, and plastic sheeting suffocates root systems. Woven weed barrier fabric can be effective at reducing weed competition, allowing moisture and oxygen to enter the soil around the tree. It does not, however, add organic matter to the soil or reduce compaction like a natural mulch. Watering: Moisture is critical to trees, but too much moisture can cause serious damage. Newly planted trees should be watered once per week (1 inch) in the absence of rain. Established trees should receive 1 inch of water every 10 to 14 days. These amounts are in addition to the water a surrounding grass lawn would need. A new tree in competition with a surrounding grass lawn may need 2 inches or more of water a week to thrive. Daily watering causes a lack of soil oxygen, smothering roots. It can reduce the number of deep roots. Larger amounts of water should be applied once or twice a week instead. Water with a hose or coarse-droplet sprinkler at a rate low enough to keep water from running off. Most tree roots are not very deep (within the upper 6 to 12 inches of soil), and deep roots will receive water if enough is applied to the soil surface. Fertilizing: Fertilize trees only when necessary. If growth is adequate and steady, foliage appears healthy and there has been no major disturbance around the tree, no fertilization is needed. When fertilizing is necessary, slow release, balanced, granular fertilizer or soil-applied liquids should be distributed over the tree's entire root zone. Applying fertilizer through holes augered into the soil or with fertilizer spikes is not recommended. Routine trunk injections of fertilizers into healthy trees are not recommended. Pruning: Every tree has different pruning requirements. Here are some important considerations in minimizing tree damage when pruning or dealing with wounds. Natural Target Pruning: When pruning trees, it is important to make final cuts at the proper location. Cuts should be made from just outside the branch bark ridge (readily visible on most species) to just outside the swollen branch base or branch collar. A cut between these "natural target" points removes all branch tissue but does not cut into trunk wood. Leaving stubs leads to unwanted sprouting and decay of the remaining stem tissue. Cuts made too close (flush cuts) leave much larger wounds than proper cuts and can cause dieback of the surrounding cambium. As a result, flush cut wounds do not heal properly, causing major damage to the trunk from which the tree may not recover. Avoid over-pruning trees. Prune lightly once a year for several years rather than heavily all at once. A good rule-of-thumb is to prune off no more than about 25 percent of a tree's foliage in one year. Also try to avoid having to prune branches that are over one to two inches in diameter. Tipping branches usually causes more problems later on--it is better to remove entire branches back to the trunk. Pruning branches when they are small makes smaller wounds that close quickly. When branches die, they should be pruned back to the nearest live branch, and no stub should be left. Take care not to injure the branch collar or any callus that may have formed since the branch died. Maintenance Pruning: Trees should not be pruned unless there is good reason for pruning. Reasons may include safety, removal of dead or injured branches, correction of a structural defect, or interference with utility lines. Removal of healthy branches to "thin" a crown or for similar reasons is never necessary. Topping trees or stripping live branches from inside a tree are dangerous practices that can severely impair tree health and longevity. CODIT -- Compartmentalization Of Decay In Trees -- is a concept used to describe the reactions that take place in a tree in response to wounding. When a tree is wounded, it sets up defensive walls against the invasion of decay fungi and other microorganisms. The vessels near the wound are plugged with gums, resins and chemicals that resist the spread of decay. The living tissues outside the wounded area then begin to form a callus layer in an attempt to close the wound. A properly made cut results in a doughnut-like ring of callus forming all the way around the wound. Wound closure for small wounds may take only a few months. Larger wounds may take years to close, or may not close at all. Other Wounding Agents: Use of Mowers and Other Yard Equipment: Trees often are wounded by careless use of yard equipment like mowers, weed whips, and other trimming equipment. These injuries cut through important vascular tissue just inside the bark, which can lead to decay and ultimately death of the tree. A bed of natural mulch around the tree eliminates the need to trim or mow close to the tree's base. Extreme care should be taken when digging up or tilling the soil under a tree. Many large and small roots will be cut by such digging, especially if it occurs close to the trunk. Trenching and Excessive Change in Soil Grade: Trenching next to trees cuts major roots. Where possible, tunneling should be used to leave the upper 18 inches of soil undisturbed. When tree roots must be cut they should be cut cleanly. Ripping or tearing tree roots with a backhoe or other implement leaves large open wounds or may shatter roots, preventing the formation of new roots. Changes in soil grade can seriously injure trees. About 90 percent of the tree's root system lies within the upper 18 inches of the soil. Covering tree roots with as little as 3 inches of soil can cause damage by suffocating roots. Filled areas should be properly tiled and graveled to allow for air movement and drainage. Animal Damage: Animals can cause wounds, especially on smaller trees. Field mice (voles), rabbits, squirrels and deer commonly feed on the young bark of trees during the winter when food sources are scarce. Animal damage can be prevented by excluding the animals from the area around the tree. This can be done with a simple wire fence around the tree or yard. Discourage rodents by using a plastic tree guard around the trunk. Check yearly to ensure that the guard is not girdling the trunk. Insect Damage: Insects can cause several types of wounds to trees--some bore directly into the main stem and branches, others feed on young shoots and leaves. Inspect trees regularly for signs of insect damage. When damage is noted, take care to identify the problem properly and use appropriate controls. Injury Treatment: Cavities and Drainage Tubes: Cavities in trees require only minimal care. Clean out any loose wood or debris. Check the cavity for carpenter ants or termites. These insects should be controlled as necessary. Do not fill the cavity, but rather allow it to remain open. Do not scrape the inside of a cavity to remove dead wood. This may expose live tissue and re-wound the tree, allowing decay to spread. Drainage tubes should not be used in trees. Drilling holes to drain water from interior cavities opens a path for new decay. Wounds: Wound treatment should be confined to removal of loose bark or wood. Leave the wound exposed so the tree may begin the natural process of callus formation and healing or sealing over. "Scribing" a wound in an elliptical shape once was recommended to help water and nutrients flow around the wounded area. This is no longer recommended since it only makes wounds larger and does not improve sap flow. Wound Dressings: Wound dressings are not recommended for any tree wounds. Wound dressings actually have been found to increase decay. Wounds should be left exposed to the open air to seal naturally. Injections and Implants: Some insects, diseases and nutrient deficiencies can be controlled through the use of chemical injections or implants. These measures, however, require drilling holes into the trunk and should be used only after all other available treatments have been considered. Since injection holes are wounds, they should be made in accordance with manufacturers' recommendations to minimize the damage they cause. Injection holes should be kept as small and as shallow as possible and injection should not be repeated more than once every two or three years, except in severe cases. Injection points should not be filled or treated with wound dressing after treatment. Cabling and Bracing: Trees that have severe structural defects or that have suffered serious damage sometimes can be saved by cable and bracing techniques. In all cases cable and bracing should be done by a professional arborist who is familiar with this technique. Not only can improper cabling or bracing result in damage to the tree, it can also be very dangerous. Hazard Identification: Trees that have large, dead branches or show signs of interior decay should be inspected by a professional forester or arborist. These trees can become major liabilities if left standing. Accidents can often be prevented through proper pruning. Tree work can be dangerous, and many tasks should be left to professional arborists.
Adapted from Dave Mooter and Mike Kuhns, Nebraska Extension, 2000
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