Trees and shrubs must be selected for quality, which can be determined through thoughtful inspection. Quality factors to evaluate include root ball size and structure; trunk form and strength; branch structure; and evidence of injury, disease or poor cultivation methods.

Choosing the Right Tree Size

Water must be supplied on a regular basis to newly planted trees. Smaller trees will require regular irrigation for several months following planting, larger trees for much longer. If you cannot meet the watering requirements of a given tree, choose it in a smaller size.

Site drainage also affects the size of tree to choose. On poorly drained sites, smaller trees with shallower root balls often do better than large nursery trees. A nursery tree is considered large if its trunk is more than 2 inches in diameter. The larger root balls of big trees can become submerged in water on a poorly drained site. This will kill the roots at the base of the root ball and stress the tree, slowing the rate of establishment and thus making it more sensitive to pests, disease and drought injury. If large trees are absolutely necessary for a poorly drained site, select trees especially grown with a shallow root ball or plant in a shallow hole to keep roots above the water level.

Root Ball Characteristics

The shape, depth and size of a tree’s root ball is determined by the way the tree was produced in the nursery. Trees grown directly in the ground are called field-grown. Trees may also be grown in containers that are made in sizes, shapes and materials that affect the structure of the root ball. When a tree will be planted in a well-drained site and receive regular irrigation, the way it was produced doesn’t really matter. However, when watering will be infrequent, the method by which a tree was grown or harvested will affect its chances of surviving transplanting.

Field-Grown Trees

Field-grown trees that have been properly harvested and hardened off are strong and sturdy. They are good choices for any kind of site and usually the best choice for sites where watering will be infrequent or irregular. Compared to trees grown by other methods, the root ball of a harvested field-grown tree is larger and capable of more water storage, thus making it slower to dry out. The root balls of field-grown trees are also much heavier than those of container-grown trees, making them significantly harder to handle.

When field-grown trees are harvested, burlap is wrapped around the root balls and secured with nails, string or wire. The root ball of a balled-and-burlapped tree is fairly durable, but care should be exercised to avoid breaking or crushing roots in transport and handling.

Container-Grown Trees

Container-grown trees have smaller root balls and many times more fine roots than similarly sized field-grown trees. For a variety of reasons, container-grown trees dry out more quickly, making them more sensitive to drought injury in the period following planting.

Fabric containers or fabric bags are made of a heavy flexible fabric especially designed for this growing method. Trees are planted in the fabric containers that are then planted in the ground. While their smaller size makes them easier to handle, they are also more fragile and dry out faster than the root balls of balled-and-burlapped trees.

Trees and shrubs are most commonly grown in plastic containers that are placed either above ground or, more recently, below ground and inside permanently installed containers with specially designed drainage holes. This latter method, known as pot-in-pot, insulates the root system and should produce roots that are more uniformly distributed than those found in above-ground containers.

Containers are usually filled with an artificial or soilless growing medium composed of one or more materials like bark, peat moss, compost and sand. These media are generally coarser than soil, which permits them to drain quickly and which, in turn, helps prevent root rot. To maintain optimum growth after planting, water container-grown plants at least as often as they were watered in the nursery. In the summer, it may be necessary to irrigate daily on well-drained, sandy soils for a number of weeks or months after planting, especially for trees whose trunks are over 2 inches in diameter. Taper off on watering as roots grow out into the landscape soil.

Bare-Root Trees

As the name suggests, bare-root trees are sold with roots that are not encased in soil. They are field-grown, hardened off trees and are not commonly found in the market. If their roots are kept shaded, moist and cool until planting, bare root trees should perform as well as container-grown or balled-and-burlapped trees.

Checking the Root Ball for Defects

The health of a plant’s root ball is critical to its ultimate survival. Some root ball defects are obvious, while others require careful observation and inspection to discover. A thorough inspection before planting will help prevent future disappointment.

One defect can be easily diagnosed without removing soil or the growing medium from the root ball. Remove any stakes from the tree and simply push the trunk back and forth once or twice while holding the root ball still. The trunk on a tree of good quality will bend along its length but will not move in the soil or medium. The trunk on a tree with a defective root system will pivot at its base before it bends or will appear to be loose in the root ball. A tree with this defect may not develop enough stability to hold itself up.

Next, check for the location of the top layer of the tree’s roots, which should be very near the surface of the soil. Slip your fingers along the trunk and down into the soil until you feel the first root growing from the trunk. This should be no more than an inch or two below the surface of the soil. Sometimes trees have been planted too deeply either in the ground or in containers. The raised soil level can hinder the tree’s establishment in the landscape or can cause its decline several years later. If for some reason you are compelled to plant a tree with a raised soil level, remove all soil to expose the topmost root in the root ball. Plant the tree so that this root is just below the soil’s surface.

Check the main roots close to the tree’s trunk. Look for kinked or circling roots close to the trunk and near the soil surface. If circling roots are tight up against the trunk, do not purchase the tree. Circling or kinked roots less than about one-third the trunk diameter can be cut at the point where they begin to circle. This may temporarily slow growth but should have a positive impact on future tree survival and growth.

Inspect the bottom of the container for escaping roots. There should be no evidence of escaping roots larger than about one-fifth the diameter of the trunk of the tree. Smaller escaping roots may be cut off with little harm to the tree. If the larger roots exist and need to be cut to remove the tree from the container, the tree could suffer decline and leaf drop. If you try to pick up a container-grown shrub and find that it is fastened to the ground by escaping roots, select another plant. The root ball should be free of weeds, which slow the establishment rate of a plant and may spread into the surrounding landscape.

Once you have checked the container’s bottom, lay the tree on its side. You should be able to simply slide the container off the root ball. If not, gently push the bottom of the container while holding the rim to loosen the root ball from the container. If this doesn’t free the root ball, it may be pot-bound.

Once the tree is out of the container, the root ball should stay together but be somewhat flexible. You should be able to pick the root ball up and gently place it back in the container without losing much media. If the root ball falls apart when you remove it, particularly with shrubs, it may have just been “stepped up” to a larger container. You could be buying a large container of potting media with very few roots.

If many roots circle around the outside of the root ball or the root ball is very hard, it is said to be pot-bound or root-bound. A mass of circling roots on the outside of a root ball can act as a physical barrier to root penetration into the landscape soil after planting. The circling roots can also choke and kill the tree as it grows older. Do not purchase pot-bound plants.

Examine the roots on the surface of the root ball. Do not buy a plant with black roots. These roots were probably killed by heat stress, freezing temperatures or over-watering.

With trees and shrubs that are balled-and-burlapped, note whether the root ball has been secured tightly with pins, twine or wire. A loose or droopy root ball indicates that the plant was not properly cared for and may perform poorly after planting. The trunk should be sturdy in the root ball. If the trunk is unstable or needs a stake to prevent it from falling over, the root system may be inferior. Purchase is not recommended.

Bare-root trees should have living, small-diameter roots growing from the larger roots. The insides of living roots are whitish and wet.

Trunk Form and Structure

Strong trunks are thickest near the ground and taper up. They do not require stakes to support them. Trees that were staked for a long time in the nursery may not develop proper trunk taper and may fall over when stakes are removed. The trunks of these trees are often the same diameter at the ground as they are several feet up the tree. This is a sign that the trunk may e weak.

To test for trunk strength, take the tree into an open area and remove all stakes. If the tree is in leaf and it remains erect, it is probably strong enough. If possible, simulate rainfall by wetting the foliage with a hose. This weighs the branches down and further tests the sturdiness of the trunk.

Single-trunked Trees: Trees with one trunk are usually considered stronger than their multi-trunked counterparts and are more durable in the landscape. Certain small trees such as crape myrtle (Lagerstroemia indica), Japanese privet (Ligustrum japonicum), southern waxmyrtle (Myrica cerifera) and other ornamentals usually grow with several trunks, but can be trained in the nursery to one trunk.

A tree that will grow to be more than 40 feet tall should have a single trunk well up into its canopy, but the trunk does not have to be arrow-straight. A tree that forks in its top half should have one of the trunks removed before planting. If the trunk forks in the lower half of the tree, is unusually bent or has a severe dog-leg, then it should not be planted.

Trees with a single trunk are usually more appropriate for planting along streets and near walks and are also easier to train so that the branches grow well overhead of vehicles and pedestrians. Lower branches and entire trunks on multi-trunked trees often have to be removed several years after planting because they obstruct pedestrians and traffic. This often disfigures the tree and compromises tree health.

Multi-trunked Trees: Small multi-trunked trees less than 30 feet tall at maturity have a definite place in the landscape. If their several trunks originate close to the ground, they make nice specimens, especially those trees that have attractive, showy bark or trunk structure.

Trees with several trunks often develop embedded bark in the crotches. Embedded bark appears as a crease running several inches to many feet down from the crotch. Bark is pinched into the crease. This condition can cause one of the trunks to split from the rest of the tree during a storm or even on a windy day. When a major branch or trunk splits, the character and health of the tree may be altered.

Branch Size and Arrangement: Branches should be distributed along the trunk and not clumped toward the top. Branches in the lower half of the tree help distribute the stress placed on the trunk when the wind blows. At least half of the foliage should originate from branches on the lower two-thirds of the tree.

Branches that are less than half the diameter of the trunk and those with a U-shaped crotch are stronger than those that grow larger than half the trunk diameter and those with a V-shaped crotch.

Branch arrangement and spacing is especially important on trees that will be large, over 40 feet at maturity. On saplings with trunk diameters of less than 2 inches, the main or largest diameter branches should be about 6 inches apart. Smaller-sized branches can be closer than this. Trees with trunk diameters between 2 and 4 inches might have one or two branches that will be permanent branches. Permanent branches should be spaced at least 18 inches apart and should not have bark embedded in the branch crotches. Trees with trunks larger than 4 inches in diameter are likely to have several permanent branches that should also be at least 18 inches apart.

Branch arrangement and spacing is less crucial on trees that will be small at maturity. Simply look for those with a pleasing branch arrangement that will fit the needs of the planting site.

Signs of Disease and Injury: Examine a tree’s leaves, trunk and branches for evidence of disease, pest infestation or other injury. Not only do you want to select a tree that is healthy, you also want to avoid exposing the other plants in the landscape to an un-healthy plant.

Pest Problems: Many mites and insect pests are tiny and/or well-hidden. Look carefully at both sides of a tree’s leaves, especially if the foliage is speckled or spotted. Speckling may be the result of a generally armless leaf spot disease. Spotted foliage may also be an indication of sunburn or chemical injury or possibly an infestation of scales, spider mites, lace bugs or some other pest that sucks sap from the foliage. Do not purchase trees with these pests. If you are not certain of the cause of leaf speckling or spotting, ask the nursery manager.

Because their color is often similar to that of twigs and branches, the presence of scale insects is one of the more difficult infestations to detect. Look for raised ridges or bumps on the tree’s twigs. Do not plant trees with scale infestations.

Except in their dormant season, nursery trees should have foliage to the ends of all their branches. Dead tips indicate problems that need further study. If the tree is dormant and has no leaves, scrape several of its twigs with your fingernail. If the tissue revealed is greenish or white, the twig is alive. Dry brown tissue indicates that the twig or branch is dead from that part out to the tip. This condition is known as dieback. As a rule, trees with dieback should not be purchased.

Injuries and Cultivation Damage: Avoid trees with scars and other open wounds along the trunk. Open pruning wounds are fine if they are small, but the presence of large open pruning wounds could indicate a poor or unplanned pruning program at the nursery. Small broken branches should be pruned back to healthy tissue. Trees with large broken branches should usually be left at the nursery. Do not purchase trees with bark stripped down the trunk from an improper pruning cut.

Check for injuries to the trunk from stakes rubbing against it, and be sure the tree was not harmed in the nursery by stake ties that were left on for too long. By the time of purchase, a tree should usually be able to stand without stakes.

Leaves should be colored like those of other trees of the same type. If leaves are smaller, lighter colored or yellower than others, the tree may lack vigor and grow poorly.

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Each plant in the landscape has its own growth habit and different requirements for pruning. Some plants are pruned routinely to maintain a desired size or shape. Others are pruned to promote healthy vigorous growth, flowering or fruiting. Sometimes it is necessary to prune shrubs that overgrow their sites, crowd other plants or limit the view from windows. Plants damaged by insects, diseases or freezing injury may require corrective pruning.

Improper pruning or pruning at the wrong time of year can result in misshapened plants, reduced flowering or plants that are more likely to be damaged by insects, diseases or winter cold. It is important to learn about the three T’s of proper pruning: tools, timing and technique.

Pruning Tools

Like other products on the market today, pruning tools are available in a wide range of brand names, styles and prices. When purchasing tools, shop for quality and durability before price. Look for tool manufacturers that provide replacement parts on request and offer warranties against faulty materials and workmanship.

Most pruning tasks in the landscape can be accomplished using hand pruners, lopping shears, pruning saws, pole pruners or hedge shears. There are two basic types of hand pruners: (1) Scissor-action or bypass pruners, and (2) Straight-anvil pruners. Scissor-action pruners have a sharpened blade that cuts by gliding against a thicker sharp blade. Anvil-action pruners have a sharp blade that cuts against a broad, flattened, grooved blade. Scissor-action pruners usually cost more than anvil-action pruners but they make closer, smoother cuts. Anvil-action pruners can make larger cuts easier than scissor-action pruners. Hand pruners cut small twigs and branches up to one-half inch in diameter.

For larger branches, one-half to 1½ inches in diameter, lopping shears are best. Lopping shears, sometimes called loppers, are like scissor-action hand pruners except they have larger blades and long handles that increase leverage. When using loppers, cut in one smooth stroke to avoid injuring the branch.

A pruning saw is used for branches larger than l ½ inches in diameter. A pruning saw has a narrower blade for easier maneuvering and coarser points or teeth than a common carpentry saw. Most pruning saws also have curved blades that cut on the draw stroke (pulling the blade toward you).

Pole pruners remove branches from trees that cannot be reached from the ground. Most pole pruners have both a cutting blade and a saw. The cutting blade is operated from the ground by a long rope or lanyard that is pulled downward. The pole can be made from aluminum, fiberglass or plastic. Some poles fit together in three 6-foot sections, while newer models have a telescoping type of extension. Because of the risk of electrocution, avoid using aluminum-handled pole pruners near power lines.

Use hedge shears (manual, gasoline-powered or electric) to shear or clip hedges or other plants when you want a neatly trimmed appearance. Do not attempt to cut large branches with hedge shears.

To keep all pruning tools in good shape, sharpen and oil their blades at the end of each season. When sharpening loppers, hedge shears and scissor-action hand shears, sharpen only the outside surfaces of the blades so the inside surfaces remain flat and slide smoothly against one another. It is best to have pruning saws sharpened by a professional. Oil blades by wiping them with a cloth saturated in household oil, and treat wooden handles with linseed oil.

Pruning Time

Because flowering ornamentals form their flower buds at different times of year, pruning times must be adjusted accordingly. Many spring-flowering plants such as azalea, dogwood, forsythia, redbud and rhododendron set flower buds in the fall, so pruning during the fall and winter months eliminates or decreases their spring flower display. Plants that typically flower during the summer form flower buds on new growth and can be pruned during the winter with no effect on their flowering. Examples of this type of plant are crape myrtle, hibiscus and abelia.

As a general rule, plants that flower before June 1 should be pruned after they bloom while those that flower after June 1 are considered summer-flowering and can be pruned just prior to spring growth. One exception to this rule is the oakleaf hydrangea, a summer-flowering shrub that forms flower buds the previous season. Late-flowering azalea cultivars that bloom during June or even July are another exception. Prune both the oakleaf hydrangea and the azalea cultivars after they bloom.

For further information on suggested pruning times for selected flowering trees and shrubs, refer to the fact sheet Pruning Shrubs, HGIC 1053.

Ornamental plants that are not grown for their showy flowers can be pruned during the late winter, spring or summer months. Avoid pruning during the fall or early winter because pruning in fall encourages tender new growth that may not be sufficiently hardened to resist the winter cold.

Some shade and flowering trees tend to bleed or excrete large amounts of sap from pruning wounds. Among these trees are maple, birch, dogwood, beech, elm, willow, flowering plum and flowering cherry. Sap excreted from the tree is not harmful, but it is unsightly. To minimize bleeding, prune these trees after the leaves have matured. Leaves use plant sap when they expand, and the tree excretes less sap from the wound.

Pruning Technique

To understand why one pruning technique is preferred over another for a particular plant and why cuts are made the way they are, it helps to understand a basic physiological principle of pruning. The terminal bud — the bud at the end of a branch or twig — produces a hormone called auxin that directs the growth of lateral buds — buds along the side of the branch or twig. As long as the terminal bud is intact, auxin suppresses the growth of lateral buds and shoots behind the terminal. However, when you remove the terminal bud by pruning, lateral buds and shoots below the pruning cut grow vigorously. The most vigorous new growth always occurs within 6 to 8 inches of the pruning cut.

Prune Plants Either by Heading Back or by Thinning

Heading back (Figure 1) or stubbing trees is rarely warranted in landscape sites and often results in undesirable multiple leaders or trunks. If it is necessary, for instance, to prune beneath power lines or to clear a tree from interfering with a structure, always prune back to a fork where there is a live branch that is at least half the diameter of the limb being removed. This technique is called “drop-crotching.” Within several months, prune out all sprouts growing in response to the cut. Never “hat-rack” a landscape tree by cutting all of its branches back to an arbitrary length. This type of pruning has no place in horticulture.

Figure 1

Thinning (cutting selected branches back to a lateral branch or main trunk) is usually preferred over heading back (Figure 1). Trees can be thinned to increase light penetration and encourage turfgrass growth beneath the tree. First, remove branches that are rubbing, crossed over each other, dead, diseased or dying. Removing upright branches creates a more spreading tree while removing horizontal branches results in an upright form. If further thinning is desired, remove branches back to major limbs to create an open crown. This is a specialized technique best performed by a professional arborist. Space remaining branches along the major limbs so that each one has room to develop. Trees with properly thinned crowns resist wind damage better than unpruned trees.

Making the Cut

A second physiological principle helps explain what happens when you make a pruning cut. When you cut a branch back to the main trunk, to a lateral branch or to a lateral bud, a higher concentration of hormones in these areas causes the wound to heal rapidly. When you leave a stub, the distance from the hormonal source increases and the wound heals slower, if it heals at all. Insects and diseases may enter the cut portion of a stub and cause it to die back.

Therefore, regardless of whether you are pruning a small twig or a large branch, you can avoid leaving a stub by always cutting back to a bud, a lateral branch or the main trunk. When you prune back to a bud, make the cut at a slight angle just above the bud. This allows moisture to flow readily off the wound. A hormonal stimulus from the nearby bud accelerates the healing process. However, avoid making the cut at a sharp angle because it will produce a larger wound.

Selecting Branches to Be Pruned

Become familiar with the characteristic form of your tree before removing any live branches. In many landscapes, little or no attempt should be made to significantly change these characteristic growth habits. Instead, prune in such a way as to enhance and encourage the natural shape of the tree. First remove dead, diseased or broken twigs and branches. Now study the tree’s form and select the best-spaced and positioned permanent branches, removing or shortening the others. To shorten, use thinning cuts. Permanent branches should be spaced 6 to 24 inches apart on the trunk, depending on the ultimate mature size of the tree. On smaller trees like dogwoods, a 6-inch spacing is adequate, whereas spaces of 18 to 24 inches are best for large maturing trees like oaks. Remove fast-growing suckers that sprout at the base of and along tree trunks or on large interior limbs.

To prune a young tree to a single leader (the stem that will become the trunk), locate the straightest and best leader to retain. In shaping the tree crown, remove lateral branches that are growing upright. They will compete with the leader and form a weak, multi-leader tree. Most trees can be grown with a single leader when they are young, but the growth habit of some species will change to a multiple leader spreading form at maturity. There should be no branches leaving the trunk at an acute angle or narrow forks either between branches or between a branch and the trunk. Branches that are less than two-thirds the diameter of the trunk are less likely to split off than larger branches.

When training a young tree, prune back those branches below the lowest permanent branch 8 to 12 inches from the trunk; these are temporary branches. Remove any lower branches that are larger than a quarter-inch in diameter. By keeping the smaller-diameter branches on the trunk, the tree will grow faster and develop a thicker trunk. The trunk will also be better protected from sunburn and vandalism or accidental damage. Removing the lower branches too soon will result in a poorer quality plant. When the tree trunk approaches 2 inches in diameter (measured 6 inches up from the ground), remove the temporary branches.

Once the framework (trunk and main branches) of the tree is established, some annual maintenance pruning is required. Each tree is different in its growth habit, vigor and pruning requirements, but there are some general considerations that may help direct your pruning decisions:

• A major limb growing at a narrow angle to the main trunk (less than a 45-degree angle) is likely to develop a weak crotch and may split during heavy winds and ice loads. Remove branches that have narrow crotch angles.
• Remove branches that grow inward or threaten to rub against nearby branches.
• Remove branches that grow downward from the main limbs, which may interfere with mowing and other maintenance practices.
• Prune branches damaged by insects, diseases, winter cold or storms below the damaged area. Prune branches of pear, pyracantha or loquat damaged by fireblight disease several inches below the infection. To prevent spreading the disease, sterilize pruning tools between cuts by dipping the blades in isopropyl rubbing alcohol or a solution prepared from one part household bleach to nine parts water.
• Trees such as Bradford pear, ornamental cherry, crabapple and ornamental plum form vigorous shoots or suckers at the base of the trunk and many upright succulent shoots (watersprouts) along the main branches. These shoots starve the tree of valuable nutrients and detract from the tree’s overall appearance. Remove them while they are young.
• Some trees develop upright shoots, which compete with the main trunk for dominance. Remove these shoots if you want to maintain a conical or pyramidal growth habit.

Removing Large Tree Branches

Branches larger than 1½ inches in diameter require three separate cuts to prevent trunk bark stripping (Figure 2). The first cut is made on the underside of the branch about 15 inches away from the trunk and as far up through the branch as possible before the branch weight binds the saw. The second cut is made downward from the top of the branch about 18 inches from the main trunk to cause the limb to split cleanly between the two cuts without tearing the bark. The remaining stub can then be supported easily with one hand while it is cut from the tree. This final cut should begin on the outside of the branch bark ridge and end just outside of the branch collar swelling on the lower side of the branch. The branch bark ridge is usually rough, always darker than the surrounding bark, and fairly obvious on most species. The collar is a swollen area at the base of a branch. This region between the branch and the trunk acts as a natural barrier to decay-causing organisms. Note that the cut is usually made angling down and outward from the tree. If the cut must be made straight down (parallel to the trunk), do not make it flush with the tree trunk. A flush cut will cause serious injury. Although this was once standard practice, research has conclusively shown that flush cuts cause extensive trunk decay because wood that is actually part of the trunk gets cut.

Figure 2

Painting wounds with tree wound dressing has become a controversial practice. Research has shown that wound dressings do not prevent decay. When exposed to the sun, the protective coating often cracks, allowing moisture to enter and accumulate in pockets between the wood and the wound covering. This situation may be more inviting to wood rotting organisms than one with no wound cover.

Broadleaf Evergreen Trees

Broadleaf evergreens, like magnolias and hollies, usually require little or no pruning. In fact, most broadleaf evergreens develop a naturally symmetric growth habit when left alone.

You may want to prune some during the early life of the tree to balance the growth or to eliminate multiple trunks and/or multiple leader branches. Otherwise routine annual pruning is not recommended.

Pruning Conifers (Needle-Type Evergreens)

Most upright-growing plants in this group such as spruce, pine, cedar and fir have branches spaced evenly around the main trunk. They develop a symmetrical growth habit and become quite large at maturity. If planted in open areas and given plenty of room to grow, they require minimal pruning.

If you remove about one-half of the new shoots while new growth is in the “candle stage” (small immature needles packed around the stem resembling a candle), you can thicken the growth of pines and spruce. Avoid cutting back into the hardened older wood because new shoots will not grow and the form of the plant will be destroyed.

Upright and broad-spreading junipers sometimes outgrow their sites and must be reduced in size. You can make thinning cuts within the canopy to reduce plant size without destroying the natural shape. You can also shear, but shearing is recommended only when you desire formal shapes.

Like pines and spruces, junipers do not generate new growth from old wood, so you should never severely prune more than one-half of the foliage. You can reduce the length of individual branches by cutting them back to a lateral branch. This technique maintains a natural appearance while it decreases the size of the shrub.

Pruning Palms

Take care when pruning palms not to cut or otherwise injure the terminal bud or the whole tree will die. Old dead leaves on palms should be removed as they often harbor insects and rodents and may become a fire hazard. Remove palm leaves by cutting them from the underside to avoid tearing the fibers of the palm’s stem.

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The conflict between land development and tree protection seems to be a losing battle. Oftentimes, a building site has been chosen because of the presence of mature trees. These trees, however, have difficulty surviving the construction process. Although most developers would prefer to save trees on a property, they are often discouraged by past failures or regulations that force them to remove trees to locate utilities. Communication and cooperation among all participants involved in the building process (landowner, contractors, architect, landscape architect, arborist, etc.) is essential to ensure a successful tree-protection plan.

Once you have selected the trees to remain on the property, consider their location in deciding placement of the house, garage, driveway, walks and patio. Simply changing the angle of a building or curving a walk can preserve the essential root space of a prized tree. It is important at this point to be in close communication with your architect, who can help by locating buildings to harmonize with the natural terrain.

The key to the survival of trees in the years following construction is protection of the roots during construction. The three main causes of tree death during construction are soil compaction, grade changes and root severing.

Soil Compaction

Soil compaction cuts off air and water to the tree roots. The damage caused by soil compaction occurs slowly, sometimes not becoming evident for several years. To prevent vehicular and foot traffic around the roots of protected trees, erect physical barriers beyond the dripline of individual trees, or better yet, groups of trees. When this is not possible, other protective methods can be used:

(1) spreading several inches of wood chips in the root zone area; (2) bridging root areas with plates of steel. Work with the builder to locate and mark (with signs or flagging) all parking places for workers, construction roads, and areas for storage of building materials, soil and gravel.

Raising the Existing Grade

Grade changes are often necessary during construction of a new building. When the grade around an established tree is being raised, consider methods of preventing injury to the tree before the fill is made rather than attempting to take corrective measures after the damage has been done. While the initial cost may be high, prevention is always cheaper and more effective than attempting to correct the situation after damage has been done.

Remove all vegetation, including underbrush and sod, beneath the branch spread of the tree. Break up the top 3 to 6 inches of soil carefully so as to disturb the least possible amount of roots. This allows better contact between the fill and soil surface. Apply fertilizer at recommended rates.

Construct an open-joint wall of shell, brick, rock or masonry in a circle around the tree trunk, with at least 1 to 2 feet between the wall and trunk. This wall should be as high as the top of the new grade. This opening is commonly referred to as a tree well.

Construct an aeration system using 4-inch agricultural clay tile or 4-inch perforated plastic pipe arranged in five to six horizontal lines radiating from the tree well like spokes in a wheel to a point beyond the branch spread. Allow excess moisture to drain away by installing the radial lines so they slope away from the trunk. Connect the outer ends of the radiating system with a circle of tile or perforated plastic pipe. (See Figures 1 and 2.)

Figure 1. An agricultural drainage tile installation is shown with a dry well and vertical bell tile to provide aeration for tree roots beneath deep soil fill.

Figure 2. A cross section of a completed fill is shown around an established tree. Soil fill is placed over the ventilating tile system.

To provide vents, place 4- or 6-inch plastic pipe or bell tile upright over the junction of the radial lines with the circle. They should extend to the surface of the planned grade level. Extend the lower end of the aeration system to a curb or storm drain to carry excess moisture away from the root system.

Cover the exposed soil and tile system with rock or coarse gravel to a depth of 6 to18 inches, depending on the amount of fill. Follow this with a covering layer of gravel. Place a thin layer of straw, woven plastic or other porous material over the gravel to prevent soil from filtering into the gravel and stone. Fill with good topsoil to the desired grade.

To discourage rodents, fill the tree well with enough coarse gravel to cover the ends of the lines opening into the well. Also fill the upright bell tile and cover with a screen or grill.

The tree well can be left open, covered with a metal grill or wooden deck, or filled with a mixture of coarse sand and charcoal (50 percent each, by volume) to within several inches of the top. If filled with the sand/charcoal mixture, cover with pea gravel, decorative bark or other attractive material to allow air circulation through the tile system.

An alternate method can be used if 30 inches or less fill will be used. No tile or pipe is used – only gravel. Again, remove all sod and underbrush, break up the soil surface above the roots and apply fertilizer at recommended rates.
Starting at the dripline, apply from 3 to 6 inches of crushed stone or coarse gravel. Gradually increase the depth towards the trunk of the tree until it is 8 to 12 inches or deeper within 2 feet of the trunk. The gravel can reach the surface of the fill in the area extending 2 feet around the trunk of the tree. Cover the gravel with a thin layer of straw, woven plastic or other porous material to prevent soil from filtering into the gravel and sealing the air spaces. Spread good topsoil over the area to the desired depth. Use good, well-drained topsoil in making the fill in order to provide adequate aeration for normal root activity and tree growth.

Figure 3. Coarse gravel placed over the original grade will provide aeration for tree roots beneath shallow soil fill.

Lowering the Existing Grade

There will likely be less damage to a tree when the grade is lowered, unless a great amount of the root zone is exposed or removed. Removing 1 to 2 inches of soil normally will not affect the growth of a tree, especially if steps are taken to ensure that drought damage does not result from loss of roots. Use retaining walls or terraces to avoid excessive soil loss in the area of greatest root growth. When possible, spread mulch over the exposed area to help prevent soil erosion, reduce moisture loss and keep soil temperatures lower. Provide adequate water in the event of a prolonged drought.

Corrective Steps after a Fill is Made

If a fill has been in place long enough that the tree is already showing symptoms of deterioration, there is little that can be done to save the tree. If the fill was made recently, or if serious damage has not occurred, steps can be taken to correct the problem.

If the increase was greater than 12 inches, it will be necessary to install a tile and gravel aeration system as described above, excavating the soil to the original grade.

If the increase is less than 12 inches, remove the soil around the trunk, down to the original soil level, for a radius of 2 feet beyond the tree trunk. Install a dry well around the trunk to hold the fill soil in place. Drill or dig holes every 2 feet beneath the branch spread, starting about 2 feet from the well. Insert a 6-inch tile or plastic pipe and fill with coarse gravel to allow free air and gas exchange to the roots.

Severing Roots

Although some cutting of roots near construction is inevitable, much of it can be avoided with good planning and cooperation. It is not necessary to route underground utilities in a straight line from the street to the house. Careful route selection can often avoid the root systems of important trees. If this is not possible, reduce damage by tunneling beneath the roots. To reduce trenching for foundations, substitute posts and pillars for footers and walls.

Other Problems

Often when grade changes are made the terrain is altered, and there may be a change in how water drains from the land. If too much water drains into a wooded site, trees in that area may eventually die from lack of oxygen. It may be necessary to build a drainage system to maintain the previous amount of moisture that provided natural growing conditions for the existing trees. If sites are deprived of water, irrigation may be necessary to maintain existing trees.

Watch for equipment damage to limbs and trunks, and repair promptly. Chemicals and other products that are often dumped on a construction site can change the soil chemistry, weakening and oftentimes killing trees on the property. To prevent adverse effects on construction site soils:

• Spread heavy plastic tarp where concrete is to be mixed or sheet rock will be cut. These materials raise the pH, causing alkaline soils.
• Do not clean paintbrushes and tools over tree roots.
• Dispose of chemical wastes (paint thinner, oil, etc.) properly. Do not drain these wastes on site.

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