Chapter 7: It's Not Easy Being Green: Caring for Urban Trees
|It takes five years to plant a tree.
TREE SOCIETY OF ORANGE COUNTY
It's Not Easy Being Green: Caring for Urban Trees
A tree's needs are few and simple: healthy soil, air, water, and light. We all know trees have grown without human help for thousands of years. So what's the fuss? Why can't the trees we plant in the city fend for themselves? Why does it take five years of care to be sure that an urban tree will survive its infancy?
Unfortunately for the urban forest, towns and cities have not been designed by the laws of nature, but by the law of human supply and demand. Trees are included as amenities and are established in an artificial habitat that usually falls short of supplying basic needs. In this setting, trees are further stressed by pollutants and by human-inflicted injuries. It is necessary to give urban trees special care, not only for their survival and well-being but also to protect people and property from the hazards trees can become when abandoned to a hostile environment.
Urban Soils Are Not Like the Forest Floor
The urban underground habitat is particularly ill-suited for healthy tree growth. The soil is typically a mixture of subsoil, bedrock, and construction wastes, compacted to a density that eliminates 80 to 90 percent of the soil porosity through which air and water must move. Drainage is frequently so poor that routine irrigation leads to a waterlogged environment in which the roots are unable to grow. The nutrient level may be too low for normal tree growth or too high in sodium or trace chemicals, making them toxic to trees.
The living and dead look well together in woods. Trees receive a most beautiful burial. Nature takes fallen trees gently to her bosom—at rest from storms. They seem to have been called home out of the sky to sleep now.
Trees are planted close to concrete or asphalt surfaces and are routinely installed near established trees. Compacted soil conditions, and light and frequent watering schedules designed for lawns, encourage tree-root growth close to the surface, forcing the roots to grow near driveways and sidewalks. When the man-made structure becomes damaged as a result, the roots are cut back or the tree is removed.
|MORE THAN JUST A PILE OF DIRT
What Is Soil?
Soil is a mixture of mineral particles, air, water, and organic materials. The mineral particles are made of rocks battered by water, wind, heat, and cold into minute pieces. The organic materials are decaying remains of plants and animals. The solid components of soil provide thirteen of the sixteen elements that plants need to grow.
Soil particles have varying shapes and sizes, and the proportion of particle types give the soil its texture. For instance, clay particles are microscopically small, flat wafers that cling together easily. Clay soils are typically called heavy and look dark and moist. Clay particles have large surfaces that are able to hold water and nutrients, but unless the particles are clumped together, there is often little room for air between them.
In contrast to clay is sand. Sand grains are relatively large and round or irregular in shape, naturally forming large pores between the grains. Sandy soils are thought of as light and are easy to dig in, but water—and the nutrients dissolved in it—will drain away quickly. Between clay and sand is silt, and the combination of all particle types, along with organic matter, is called loam. Loam has a nearly ideal combination of soil texture and pore sizes. It usually holds a good balance of moisture and nutrients and is loose and aerated.
Water moves through the soil in air pockets between particles. When the soil is saturated, water fills the openings between particles. As the soil drains, these air pockets fill with life-giving oxygen for the roots and microorganisms. The normal combination of soil features is approximately 50 percent soil particles, 5 percent or more organic matter, and 45 percent pore space.
Plants require sixteen chemical elements for healthy growth. Three of these elements—carbon, hydrogen, and oxygen—are provided by the air and water. The other essential elements are provided by the soil, and if any are deficient, this will adversely affect the growth of your tree. Deficiency symptoms usually show up in leaf discoloration or in abnormal growth patterns; a number of problems may cause nutrient deficiencies even though all elements are present in the soil. An arborist or urban forester may be able to recognize the problem and point you toward a solution.
The acidity or alkalinity of soil, which is expressed in pH units, affects chemical reactions and can influence the availability of nutrients to the tree. Acid soil has a low pH, while alkaline is higher, with a pH of 7 being neutral. Most trees grow better in soils that are slightly acidic, while some kinds do well in alkaline soil. Find out if the pH of soils in your area may cause problems for the species you want to grow. You may want to test your soil before you plant, then choose a tree that will dike growing there! Simple and inexpensive pH meters and test kits are available at retail nurseries or garden centers. Better yet, ask a local expert for advice. Also see Resources for more on soils.
Fighting for Life above the Ground
The urban habitat can be just as harsh above ground as it is below. Overhead utility lines, buildings, and traffic-ways often occupy the space into which a tree's branches normally grow. The consequent clearance pruning is often performed with little regard for the tree's structure or health.
|A System That Works
One Citizen Forester and two TreePeople volunteers have staged their tree-care event so regularly they have it down to a science. It takes their ten-person crew only three hours to care for fifty trees over two miles of a major Los Angeles thoroughfare.
When volunteers arrive, they gather for a refresher demo, then divide into teams by task. The pruning team, which has the most sophisticated job, leaves first to get ahead of the group. The watering team follows close behind, laying out full buckets at each tree (not emptying them yet!). Two well-cleaning teams set about clearing trash and sucker growth from around the tree base. Two cleanup crews follow, picking up leftover debris and watering the trees. Two small trucks circulate around the site, distributing water and taking trash to the dumpster. When the task is complete, everyone gathers for a brown-bag lunch and debriefing.
Maintenance crews wound the bark of trees with devices for trimming grass around tree bases, interrupting the flow of food from the leaves to the roots and thereby starving roots. Mowers and other motor-driven vehicles collide with trees, and people carve their initials in bark or break off limbs carelessly, tearing away bark and exposing the wood to decay organisms.
The light a city tree receives may be all or nothing. Trees next to buildings can be shaded most of the day or subjected to full sun plus reflected light from light-colored walls and windows.
City trees are frequently doomed to short lifetimes by improper management in the production nurseries. One of the most common flaws in container-grown stock is circling roots. Trees that cannot develop a normal root system may blow down, or their roots may strangle one another.
Be an Intensive Care Unit
As a certain little frog is accustomed to reminding us, it's not easy being green, especially in the city. That's why you can make a huge difference by paying attention to urban tree care. You'll find that the amount of work required to keep a tree growing and glowing isn't very time-consuming. Many trees require only a little up-front attention to be saved from an early death or the gradual loss of health and vigor.
Tree-care operations shouldn't be perceived as drudgery, either. The nurturing of trees and plants is a soul-renewing activity, full of rewards. You'll feel a great sense of accomplishment when you look up at a towering tree and know you are personally responsible for its health and presence.
SCHEDULING TREE CARE
It's easy to lose track of maintenance tasks, because the work is spread over weeks, months, and years. Before taking the time and effort to plant the right tree in the right place the right way, do everyone a favor and keep track of the care those trees are going to receive. A tree-care schedule can ensure that all necessary tasks are done on time, especially if your trees are on private property where no regulations guide maintenance. A tree-care schedule should spell out what and when watering, mulching, weeding, monitoring, and pruning tasks need to be done.
It's also a good idea to assign each task to a specific person or group and make the responsibility clear. Some organizations keep group calendars with all tasks clearly marked. The amount of attention you pay to tree care should equal that which you pay to planting. Show your commitment to the trees!
WHAT'S GOING ON INSIDE THAT LEAF?
Leaves have a lot of responsibility: they produce food for all parts of the tree.
Leaves produce food by a chemical process called photosynthesis. It is the only natural process that makes food from substances that are not foods, and it is one of the few sources of oxygen to the atmosphere.
The materials required for photosynthesis are carbon dioxide, water, light, and chlorophyll. Cell layers inside the leaf contain millions of tiny green chlorophyll cells, which give the leaf its color. Carbon dioxide from the air enters the leaf through small openings called stomates, while water is carried up by xylem vessels from the roots. When sunlight passes through the leaf, chlorophyll captures sunlight energy and uses it to combine the other elements to produce sugars, which the tree uses for growth and storage. The other byproduct of photosynthesis, oxygen, is released through the stomates.
Leaves control the amount of water present in the tree through a process called transpiration. When water is scarce, some trees' stomates close completely or partially, minimizing water loss.
Leaves of some trees change color in the fall. Shorter days and lower temperatures cause a decrease in green pigment, so the yellow and red pigments in the leaf become visible. Air pollution may also affect leaf color. Ozone and sulphur dioxide, chief components of smog, enter through the stomates and attack the chlorophyll cells, yellowing leaves and needles.
The normal life span of a leaf ranges from less than a year to five or more years, depending on the species. Some trees lose all their leaves at the end of the growing season, then put out a crop of new leaves in the spring. Trees that shed all their leaves annually are deciduous. Evergreen trees have leaves that live for more than a year, so they remain green year-round. Most evergreen species undergo a seasonal surge of new growth in the spring, and they usually shed old leaves in greater numbers at that time. Evergreens can be either of the needle-leaf or the broad-leaf species.
WHO DOES WHAT?
Assuming responsibility for the care of all the trees you plant can be difficult if you're a zealous planter. If you can't be the one looking after the tree, it shouldn't be planted before you have a commitment from an agency, organization, or individual to provide maintenance for at least the first few years. If you plant it and no one adopts it, you must assume the responsibility for tree care. It is also more difficult to enroll someone in caring for a tree that has been planted by someone else.
Many tasks must be left to well-equipped, trained, and authorized professionals. In most instances, if an operation requires taking one or both of your feet off the ground, don't attempt it. Likewise, root pruning and sidewalk and curb repairs should not be done by a nonprofessional.
You can encourage healthy growth and head off maintenance problems by caring for trees in the following ways during the first three to six years after planting.
- watering accurately
- pruning dead or diseased limbs and sucker growth
- training to provide strong branch structure and adequate clearance for the site
- ensuring that stakes and ties are properly installed, adjusted, and then removed when they begin interfering with the tree
- clearing trash and weeds from around trunk base
- reporting conditions that require professional attention (for example, diseases, pests, or damage)
- reporting conditions caused by professional malpractice (such as topping, equipment-induced injuries, or inappropriate irrigation)
- requesting immediate replacement of dead trees
Though you are planting with every intention of being a diligent tree-care giver, there's only so much you can do without professional training. As the tree grows, it will be increasingly difficult for members of your community group to carry out the required work without help from a professional. Tree-care operations are vital to newly planted trees for the first three to five years after planting. Once the trees reach a size at which they must be pruned for clearance to city requirements or when any major work must be done, liability and safety issues require that city crews or contractors take over the job.
Care for trees planted on property other than the parkway strip is another story, as in the case of parks, vacant lots, front or backyards, flood-control channels, and play or mall areas. On these sites, maintenance is the responsibility of the planting organization, unless the agency in charge of the site agrees to take over as trees grow. All trees planted on private property are the responsibility of the property owner.
A study by Dr. K. D. Coder states that "eighty to ninety percent of the variation in tree growth is because of water supply problems." Try asking any professional how often you should water a tree. Most likely he or she will give you an answer like "get to know your tree" or "it depends. . . ." We know how it feels to be on both sides of the watering question, so we're taking a deep breath and offering a suggested watering schedule to start you off. For a tree planted in spring, water the root ball twice a week for the first month, then widen the watering basin to include the whole planting area and water weekly for the next two months.
A TREE LOVER
"The more I learned about pruning, the more I practiced on my own trees, the more I could see—almost hear- some of the trees in my neighborhood crying out for help. I found myself imagining how I'd prune a particular tree: where to make the cuts and how the tree would look. Finally I decided to just do it. I grabbed ray pruning saw and shears and a pair of loppers, walked around the block, introduced myself to an elderly neighbor, and asked if I could work on her tree. Once I assured her I was doing it for love rather than money, she gave me the go-ahead. The work took less than an hour and felt so good that I did it again with another neighbor's apple tree. Aside from doing something charitable, I've discovered that the time invested is continuing to pay me back. Nearly every day I deliberately walk by the trees to admire them and see how they're doing. The pruning was a creative act that liberated the tree's grace and beauty. Now when I walk by, I feel not just tremendous satisfaction but something else—I feel a degree of safety and warmth, like I'm in the company of friends."
Decrease to every two weeks, sticking to that schedule until fall, and water monthly throughout winter if you live in a mild climate. Water every four to eight weeks through the second and third years after planting. A tree chosen appropriately for any particular climate, once established (after about three years), shouldn't need watering more than three or four times between July and October unless there are drought conditions. Your watering schedule and the volume of water applied each time should vary with soil texture. For instance, clay soils store twice as much water as sandy soils. If your soil is sandy, irrigate sooner with less water; if heavy clay, space waterings farther apart but add more water each time.
Of course, rain must be taken into account (in general, it takes one inch of rain to soak down six inches in clay loam and the same to soak down ten inches in sandy loam, depending on how moist the soil was before the rain). Frequent overwatering can be as serious a hazard as underwatering.
HOW CAN I TELL IF MY SOIL IS WET OR DRY?
You can tell approximately how much water your soil will hold by examining the soil around the tree. The following guidelines can help in deciding whether or when to change your watering schedule. Watch leaves for signs of wilting to be sure the time between irrigations is not too long.
Check texture. Is it mostly sand or clay? Does it have a lot of fine particles, smaller than sand grains (silt)? If, as is normal, it is a mixture of these, which one is more abundant?
Smell the soil. Does it have the odor of fresh, rich garden soil or woods soil? Or does it have a rank, soured smell, something similar to a faint odor of sewer gas? Use the table at right to interpret your examination results.
Regardless of soil texture, the following conditions indicate excessively wet soil.
One way to be sure about soil moisture is to use a soil probe before watering and examine a core sample from a foot under the soil surface, both from the root ball and from the backfill soil. You should only have to do this a few times to get to know your soil's water holding capacity. Though many kinds of scientific measurement are available, watering trees is not an exact science. Your intuition will be your best watering guide! When you become a tree guardian, you'll have a heightened awareness of how much it's rained recently and how long it's been since you watered.
It's important to water deeply and slowly, using a hose or drip irrigation system. This encourages the growth of deep roots, which anchor well, make the tree more drought tolerant, and are less likely to encounter and damage curbs and sidewalks. If the water is only sprinkled on the ground, it seeps no deeper than the surface and the tree develops surface roots. If water is poured onto the ground faster than the soil can absorb, it will run off, doing the tree no good.
Pay attention to newly planted container and ball-and-burlap plants that are in leaf. During the early part of their growing season, they will need water more frequently than at the nursery. Container root balls hold less water in the ground than they do in the container. Also, the root systems of balled-and-burlapped plants are greatly reduced when the plants leave the nursery. In arid climates, watering is the most vital care you will provide for trees. Don't forget it!
Maintaining Watering Basins
Six months after planting, schedule a maintenance event to visit the trees and widen or eliminate the watering basins you built so carefully around the root ball. Check the root crown to see if it's buried, and remove that excess soil.
|The wrongs done to trees, wrongs of every sort, are done in the darkness of ignorance and unbelief, for when the light comes, the heart of the people is always right.
Pruning can ensure a structurally strong tree and help keep it healthy by removing dead, diseased, or damaged wood and branches that will grow to interfere with one another. Proper pruning can also increase the quality or size of fruits, nuts, or flowers; direct and control growth; and ensure public safety.
Every Cut Is a Wound
Every pruning cut in live wood injures the tree and opens the cut area to the possibility of infection. Every removal of foliage reduces the tree's capacity to sustain itself. Be certain, therefore, that each pruning cut will benefit the tree enough to offset the resulting injury and leaf loss and the chance of infection. Also, make each cut in a way that causes the least injury and ensures healthy recovery.
Trees can be pruned year round. Some people think that trees should be pruned when they're dormant; others advise pruning during the growing season, when the tree has energy to heal quickly. Check with an expert for information about your species' pruning needs.
Proper pruning technique takes advantages of the tree's natural protective mechanisms. A protective chemical zone resides within the branch collar, a donut-shaped bulge at the base of the branch where the trunk and branch tissues meet. When the collar is left intact after pruning off a branch, the trunk tissue is not damaged, so the trunk is less likely to become decayed.
Whether or not you can locate it on the branch of the species you're pruning, visualize this collar and cut outside it.
See enlarged section on page 158.
What to Look for
1. Forked top. If left on the tree, this will cause the development of two leaders, thus wasting growth energy. Later, as the two tops get larger, the fork may split and damage the tree.
2. Remove for street-tree clearance.
3. Parallel branch.
4. Branch growing at a sharp angle. When this branch becomes larger, it may rub on the trunk, split out, or even cause rot to develop by giving water a chance to collect.
5. Temporary branch.
6. Crossing branches. These interfere with each other's growth and create bad form.
7. Water sprouts.
8. Basal sprouting from the root crown. This saps energy from the tree, looks messy, and can collect trash.
Cutting a living branch
Make the top of your cut just outside the branch-bark ridge, if apparent, in the crotch between the trunk and branch. Angle the cut outward from the top part, roughly opposite the branch-bark ridge, to the point where the branch collar ends.
The angle formed should be equal to the angle between the branch-bark ridge and the trunk. For a branch smaller than 4 inches, if you can't find either the branch collar or the branch-bark ridge, start the cut l/8- to 1/4-inch from the source stem and angle the cut outward 10 to 20 degrees. For larger branches, increase the dimensions of the cut.
Cutting a dead branch
A dead branch still attached to a tree usually will have a collar of tissue formed around its base. This tissue is trunk tissue. Prune the dead branch outside the collar, making sure not to cut into it.
Go easy with those pruning shears! The more foliage trees have, the more they can grow. In fact, when you're pruning, never remove more than one-third of the leaves and branches; doing so will severely weaken the tree. Keep side branches unless you suspect they'll be damaged by traffic; these branches help to produce a thicker trunk.
Dead and broken limbs are your main concern, and there shouldn't be many of them. On planting day, check the tree for dead or broken limbs and for large stubs left by the nursery. Go ahead and prune them off, leaving the branch collars intact. You can always be sure that these branches should be removed.
Don't leave stubs. When you figure out where the branch collar is, cut as close to it as possible. Cutting beyond this, or leaving a stub, interrupts the circulation of sap in the branch and upsets the healing process.
Don't flush cut. A flush cut is a pruning cut that is even with the branch or trunk surface, thus removing the branch collar and cutting into tissues in the trunk. It creates a wound much larger than the collar area and opens up the trunk tissue to decay organisms.
One event put together by a TreePeople volunteer was less of a burden than a planting and produced instant results at least as gratifying as putting trees in the ground. A main thoroughfare in Los Angeles was lined with beautiful young trees in wells that were being choked by trash, weeds, and sucker growth. The beauty of the trees was virtually hidden by five-foot suckers. A day's work brought the trees back to the street. It was like creating a whole new planting of large trees—in one day.
Promote a ban on topping! Topping, a practice employed by untrained tree workers and by utility companies to protect power lines, shears off the top part of the tree regardless of branching structure, causing dense new growth that is weakly attached and increasing the likelihood of damage from wind. Topping reduces both tree value and life expectancy. If an existing tree is likely to interfere with overhead obstructions, the proper technique is to thin or shorten branches periodically to direct growth away from wires. Miles better is to plant a tree that is small when mature.
Don't paint wounds. There is no evidence that conventional wound dressings stop rot. In fact, some dressings create conditions favorable for rot. Allow the tree's protective mechanisms to work as nature designed them.
Make three cuts when removing large branches. If the branch you're removing is too large to be held and controlled with one hand while you cut with the other, three separate cuts should be made. First, to avoid having the bark tear away as the branch falls, make a partial cut one third to halfway through the branch, about a foot away from the main stem and on the underside of the limb. Next make a complete cut a little farther out on the branch to remove the bulk of it; then make the final cut just outside the branch-bark ridge and branch collar.
Removing water sprouts and sucker growth can be a lifetime commitment. Species that are naturally large, multistemmed shrubs and have been trained to a single trunk will often produce suckers around the base of the trunk. The most effective was to eliminate them is to pull them off when they are very small, ideally by removing the buds at the bases. If they get large enough to require shears or loppers, you know those suckers will rise again! Be sure you're willing to undertake this maintenance task before you purchase such a tree. One positive note: removing sucker growth can be a very satisfying work project with existing trees!
Care for your pruning tools. Dull shears or saws make jagged cuts, which are more difficult for a tree to heal. If you are pruning a tree known to be infected with a systemic disease (such as fireblight), disinfect pruning tools with household disinfectant between each cut.
Remember, pruning either shortens or removes branches, and it is permanent. Your main job is to remove dead or broken branches and sucker growth at the base of the trunk.
Training Young Trees
Another type of pruning is called training. The objective in training is to help the young tree develop a strong branch structure. Properly trained trees will require little corrective pruning as they mature. The following guidelines will help you identify trees that need training. It's best at this point to call in a certified professional or experienced pruner to help you select the main branches so that you don't mistakenly maim your favorite tree.
The growth habit of a tree and its function in the landscape determine how much it needs to be trained. Trees with a strong central leader, or main trunk, and a conical shape like conifers, liquidambar, and pin oak will probably need little or no pruning. On the other hand, round-headed trees or trees with irregular growth habits don't naturally develop a strong branch structure but can be trained as follows.
1. Keep the leader dominant. If several shoots are competing to be the tallest, select one and prune back the others. A forked top is an example of competing leaders.
2. Select the lowest main branch at a safe and appropriate height, depending on the use of the tree. (Most cities have specifications for the clearance requirements of street trees.) The position of a limb on a trunk remains essentially the same throughout the life of the tree. In fact, as a branch increases in diameter, the distance between it and the ground decreases.
3. On large-growing trees, select main branches that are at least six inches vertically apart. When parallel and spaced closely together, main branches will be long and thin and have little structural strength. Main branches should be less than three-quarters the diameter of the trunk just above the branch.
4. Remove or cut back branches attached to the trunk at a sharp angle. A wide angle between branch and trunk allows strong connective wood to form in the crotch and all around the branch attachment. A narrow angle of attachment may have bark imbedded in the crotch, leaving no room for connective wood to form and making the attachment weak. As foliage grows and makes the limb heavy, it's likely to split off and damage the tree.
5. Branches that cross one another should be removed.
6. Keep small shoots as temporary branches along the trunk for a few years. Leave small branches along the trunk below the lowest main branch and between main branches, and keep them shorter than 12 inches long. These small branches should be kept on for one to five years after planting to increase lower-trunk size and taper and to protect the trunk from sun and vandals.
|So How Do You Get Those Stakes Out of the Ground?
There's always the time-honored method of breaking off the stake and leaving the remainder in the ground, but it's not half as satisfying or as clean a job as removing the whole thing. You can force the edge of a shovel blade into some stakes at ground level and raise them, but what about the ones that are entwined in tree roots and can't be budged?
Local Los Angeles tree saver, Alex Man, has developed a tree-stake removal tool. The tool resembles a large plumber's pipe wrench. You tighten the wrench jaws around the stake, then pull the end of the tool handle back and forth (not up and down) several times to break the roots loose. An eight-foot-long wood lever (two-by-four), mounted on an adjustable fulcrum stand, slips under the tool jaws next to the tree stake. By pulling down on the end of the lever, you can pull almost any stake out of the ground. For more information on how to construct your own stake remover, write to Alex at P.O. Box 1711, Santa Monica, CA, 90406.
If you're stuck without Alex's tool, you can use a piece of chain to tie the lever to the stake and any fulcrum (rock, cement block) you can find. This method is definitely a step, back into the stone age, but it does the trick.
REMOVING STAKES AND TIES
Removing stakes and ties is an often-neglected job—even by people who plant trees for a living. Just look around your city streets if you don't believe us! There are lots of trees choking to death out there. Stakes and ties should be viewed as temporary, in constant need of removal or replacement as the tree grows. This is a valuable service that you can provide.
When you come across a tree that has the original square nursery stake still attached, remove it. If the tree can't support itself, tie the tree to support stakes loosely, in such a way that it is upright but can sway in the wind.
For trees you've planted, go back and remove the support stakes six to eighteen months after planting. If any stake is rotten or broken, or if it interferes with the tree's growth, remove it and replace it if needed.
If the tree still needs protection from outside hazards but can stand on its own, try installing protective barriers or tree guards. For seedlings and small trees, a number of tree guards are on the market; you also can make them from wire and small stakes. You can use three or four short stakes (2 1/2 feet above ground) around the trunk of a large tree to protect it from maintenance equipment. For more serious protection from vandals or vehicles, the stakes should be four to five feet tall, made of two-by-fours or equally strong material, such as metal pipe or rebar, and connected by cross-pieces at the top.
Fix ties that have broken or slipped down. Check for ties cutting into the tree. If the tree has grown around a wire, don't try to remove it, but loosen it as much as possible and cut off any free ends. Replace ties made of materials that can cut into the bark, such as wire or rope. Remove any ties you see beginning to bind, or ties on trees that can stand on their own.
WEEDS, MULCH, AND FERTILIZER
It's best to maintain an area at least two feet in diameter free of turf and weeds around the base of tree trunks. Turf and weeds compete for water and nutrients, and some produce chemicals toxic to other plants. A small turf-free zone around a tree also reduces the need for mowers to come close. After four or five years, tree roots are extensive enough that other plants close to their trunks are not as much of a problem, although mower operators should still exercise caution. One energy saving way to control weeds is to apply a thick layer of mulch.
Trees should be mulched at the time of planting. A two- to four-inch layer of mulch in a two-to-six-foot-diameter circle around the base of the tree (or within the watering basin) will control most weeds, protect the soil from compaction and erosion, conserve moisture, moderate soil temperatures, and improve the soil as it degrades.
Leave a small circle bare around the tree's trunk to deter fungus, diseases, and rodents. Mulch should stay in place for as long as possible.
Mulch is commonly made of organic substances, such as composted or shredded bark, wood chips, dry leaves, dried lawn clippings, or similar materials. Inorganic mulches such as decomposed gravel, pea gravel, marble chips, and concrete well covers do not need to be replaced and are usually better suited for trees along city streets than for those in home landscapes.
Much debate surrounds the use of fertilizers. Some professionals recommend no soil amendments or fertilizer be added to trees, since the tree must ultimately adapt to local conditions. Others recommend the application of fertilizer to furnish essential nutrients, especially if the tree is under stress or producing food. Nitrogen is almost always deficient in the soil, and some tree experts feel that a modest amount of nitrogen should be applied to trees regularly. If you suspect fertilizer is needed, take foliage exhibiting mineral-deficiency symptoms to your local nurseryman and determine the plant's exact needs. See Resources for further information.
|WHAT'S GOING ON UNDERNEATH THAT TREE?
Roots have two important jobs to do. They anchor the tree to the ground so that it can stand erect, and they absorb water and nutrients for all the processes that take place in the tree, from photosynthesis to root growth. Roots will grow best wherever they can find water, oxygen, nutrients, and warm temperatures—typically within the top three feet of soil. Contrary to the popular myth, the root system does not mirror the tree above ground. A better analogy is to imagine the complete tree as a wineglass set on a dinner plate, with the roots extending far beyond the crown.
There are two main types of roots: absorbing roots and structural roots. Absorbing roots are masses of fine feeder roots that take in water and nutrients. They cover an area several times the leaf spread of the tree, but they seldom grow thicker than 1/8 inch and may live only a short time. Absorbing roots grow in horizontal fans near the soil surface. These fans are eventually attacked and consumed by soil organisms.
Structural roots provide the framework for the root system. There are several major roots on a tree, radiating outward and downward from the base of the tree. They are woody, grow thicker every year like branches, and have bark. Structural roots primarily grow horizontally and seldom grow deeper than 3 to 7 feet.
MONITORING FOR PROBLEMS
For the first year after planting, inspect your trees every month when watering. For the following two to four years, try to inspect your trees every six months. It takes at least one full growing season for trees to adjust to a new site after transplanting (not including the season of planting), so problems may not show up immediately. They may begin when the roots grow beyond the root ball and into the surrounding soil.
If you find a problem or potential problem, get help immediately! Sources of assistance include local nursery people, landscape professionals, university-extension or agricultural commissioners' offices, and private groups. When providing an expert with information about your tree, start by naming the tree species and then describe the problem. What are the symptoms? Is any part of the tree dead or dying? Are there mushrooms at its base? Is the trunk scraped or girdled? If possible, take a photograph of the tree parts that exhibit symptoms of illness of damage. Take a sample of the infected foliage with you, showing the arrangement of leaves on the stem and both healthy and diseased tissue. A thorough tree inspection may uncover evidence of:
- pest or disease infestations
- inhibited or stunted growth
- binding or restriction due to stakes and ties
- broken, dead, or diseased branches
- inadequate clearance from traffic under and around the tree
- wilted, curled, or distorted leaves or dried-out buds
- leaf color abnormalities (spots, yellowing, or brown margins); early leaf drop
- cracks in bark from sunburn
- sucker growth at the base or on the sides of the tree's trunk
- holes or substances oozing from the trunk
- a sickly appearance; lack of normal leaf luster or sheen
- a site that appears unmaintained or abandoned and invites vandalism
- litter or weeds around the tree base
- dead or dying trees nearby, which may infect surrounding vegetation
- severe erosion, sunken holes in the root-ball area, or an inadequate watering basin that threatens the young tree's water supply
- flooding or poor drainage
- holes, gouges, or strange growths that might indicate disease or vandalism
- surface roots beginning to grow
- algae or mosses around tree base, indicating excess watering
- burrowing rodents, such as gophers and ground squirrels
- a heavy layer of soot or particulate matter from air pollution (can be hosed off)
If you're not certain how to treat the tree for whatever problem your inspection reveals, contact a tree professional. Take a moment to prepare yourself for the person's questions by collecting the following information.
- How and when the tree was planted. Sometimes a problem may be as simple as the fact that the tree container was never removed!
- Water and drought history. The effects of drought or letting the tree's roots become extremely dry may not show up until months or years later.
- Previous uses of the site. If the area was used for parking, cars may have compacted the soil. If the site was used for garbage disposal or storage of old oil or machinery, the soil may be contaminated with chemicals.
- Activities at surrounding sites. If a neighbor has recently fumigated or applied herbicide to his or her soil, it may be the cause of your tree's poor health. If a surrounding parcel or building has been treated for a pest infestation, it might have caused pests to migrate to your trees. If neighbors have overwatered, runoff from their yard may cause problems for your trees.
- Care of surrounding vegetation. What nearby plants are receiving fertilizer? Does nearby vegetation drop leaves that make the soil acid?
- History of growth. How old is the tree? Has the weather recently been abnormal? Was past growth especially vigorous or slow? Was the tree ever blown over or severely cut back?
CHOOSING A TREE-CARE PROFESSIONAL
Unfortunately, some people enter the tree-care business with no experience, training, or certification. While it's a toss-up as to whether they leave your tree looking pretty or decimated, either way they could unknowingly cause severe, irreparable damage. Topping or unintentional disease spread can lead to future liability and an ugly tree with all sorts of potential health problems.
Fortunately, a way exists to tell a tree-care professional—one who'll know how to prune or properly diagnose and treat your tree—from those who are just in the business of cutting, topping, shaping, and cleanup. The International Society of Arboriculture (ISA) is a professional association that provides a number of services, including a testing and certification program. Those in the business of tree care must demonstrate a certain level of competence, knowledge, and experience to be certified.
Ask to see ISA certification but don't stop there. Make sure to get and check a couple of references. It's not even too extreme to actually look at the work that's been done by someone you're planning to hire to ensure that your aesthetic styles match. Good tree care is expensive. Make it worth every penny.
A PRAYER FOR TREE CARE
Now that you know what it takes for trees to be planted and grown in urban environments, you'll begin to notice the trees around you. You'll notice not only the beautiful shapes, colors, flowers, and fruits of the trees in your city but also the bad pruning, stakes that need removal, unkempt tree wells, and trees dying from wounds, drought, and pollution. Become a special kind of gardener—a tree guardian. Start caring for trees the way you care for your friends, your body, and your car: give them the care and love needed to keep them alive for you. Begin by finding one tree in the city that speaks to you, then wash its leaves, give it a drink, and see if it needs any special care. Then take on another and another. Check up on them every once in a while to see how they're doing. To quote a recent six-year-old participant at TreePeople, if you take care of trees, they'll take care of you.
Copyright 1990 by TreePeople with Andy and Katie Lipkis
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