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Vertical Mulch Preparation

Tree Root Structure International Society of Arboriculture All trees are sensitive to root disturbance. Examples include construction, landscaping, sprinkler installation, and grade changes. The effects of these changes on pre-existing trees can be quite devastating and can take five to ten years to become fully visible. To understand how trees are affected by root disturbance it is important to understand the structure of a tree’s root system. Ninety percent of the root system is located in the first 12 to 18 inches of soil. The roots extend radials from the trunk one to two times the height of the tree. During construction, the root system is cut to install foundations, sidewalks, driveways, utilities, pools, landscape beds, and irrigation systems. The closer to the tree the construction occurs, the more destructive it is. 


These roots anchor the tree and keep it from falling over. The structural roots begin at the base of the tree called the root flare. They grow mostly horizontally in the soil and taper in diameter as they move away from the tree. The cumulative mass of the root system keeps the tree upright, not just the tap root. The tap root can dissipate over time and is replaced with a series of sinker roots (smaller tap roots) through the entire root zone.

In conclusion, the closer to the trunk roots are cut, the higher the chances the tree will be unstable and fall over. A good rule of thumb is to stay approximately 6” to 12” from the trunk for every inch in diameter the tree is at DBH (diameter at breast height or 4.5’ above grade) For example: A 16” Live Oak requires a construction free distance of 8’ to 16’ from the trunk. Your certified arborist can assist you in deciding the critical distance depending on your individual situation.  

Root damage from construction  These roots are the small fibrous roots that absorb water and minerals. The more of these roots that are destroyed, the more the tree’s ability to feed itself is impacted. Cutting roots is not the only way these roots are killed. Damage also occurs through compaction of the soil from heavy equipment repeatedly driving over the root zone or supplies being stored under the tree. Compaction of the soil reduces the pore space between soil particles, eliminating the oxygen in the soil which causes root death. Signs of feeder root damage are small pale colored leaves, leaves turning brown on the edges or shedding early, and the tips of  the limbs dying over time.  In general, it is recommended not to remove more than 20-30% of the tree above and below ground at a given time. 

Tree species react differently to construction changes, but all trees take several years to acclimate and recover. The most common damage following construction is from irrigation installation and over-watering. Sprinkler installation can cause just as much damage as initial construction due to the amount of trenching in the root zone. When laying out sprinkler lines, limit the trenching across the root zone under the trees. Radial trenching can aid in this process. 

After all of the construction is completed and the irrigation is installed, it is critical to not over water the existing trees. Most of our native trees are adapted to dry conditions and are adapted to receiving approximately 30” of rain a year. When an increase in water occurs, the soil can stay saturated, reducing the amount of oxygen. Roots begin to rot in this anaerobic condition, and trees can decline or die. 

Clay soils stay saturated longer than sandier soils. It is recommended to limit watering to 1” of water a week during the growing season including rainfall. This allows the soil to be moistened and then dry out, mimicking our region’s natural rainfall pattern. Remember slope, drainage, rainfall, and sun exposure will vary the frequency and duration of the sprinkler system schedule. It is also helpful to match the water.

Soil Injection

When it comes to fertilizing trees, you'll find no shortage of options and decisions. You have choices of how and how much fertilizer to apply, what its nutrient content should be and much more. Examining all these options, for which plenty of differing opinions exist, could fill a book. So to provide a brief yet useful step-by-step guide to tree fertilization, this article will focus on the most common method: liquid injection. Liquid injection involves placing fertilizer as a liquid suspension or solution into the soil around the tree. One advantage of liquid injection is that by applying fertilizer below the soil surface, you can make certain that nutrients, such as phosphorus, are more available to tree roots by placing them below the thick turf zone.           

Most managers' choice if you are like most grounds managers, once you've decided on performing liquid injection, you will use a fertilizer that is primarily slow-release but also includes some fast-release components. 

For a general rule of thumb in determining how much nitrogen to apply, use the rate suggested by the forthcoming American National Standards Institute (ANSI) A300 guidelines: 2 to 6 pounds (0.9  to 2.7 kg) of actual nitrogen per 1,000 square feet. The ANSI guidelines also suggest injection spacing and depth levels: 18 to 36 inches apart and 4 to 12 inches deep.  Of course, it goes without saying that you'll also need the proper equipment to perform liquid-fertilizer injections, which basically means a truck with a pressurized pumping system.   

Determine how much fertilizer to inject before you can begin the injection process, you must calibrate the probe. That is, you must determine the amount of fertilizer to deliver per injection point. To do so, you need to consider the following: *Injection spacing *Analysis of the fertilizer (specifically the amount of nitrogen) *Mixing rate of raw fertilizer per 100 gallons (378.5417 Ltr) (described on the fertilizer container) *Rate of nitrogen per 1,000 square feet *Probe flow rate (how many gallons per minute flow through the probe). You can determine the probe flow rate by observing how fast the probe fills a 5-gallon (18.9 ltr) bucket and dividing the number of minutes, or fraction thereof, into 5. 

Knowing this information, let's consider an example to get started. Imagine you have the following factors: *3-foot injection spacing *26-3-13 fertilizer (26 percent nitrogen) *Mixing rate of 20 pounds (9 kg) (of fertilizer per 100 gallons *Desired nitrogen rate of 2 pounds (0.9 kg) actual nitrogen per 1,000 square feet *A 9- x 9-foot area to fertilize. Now run the math: A 9- x 9-foot area is 81 square feet. With a 3-foot spacing, the area will contain nine injection sites.  
You want 2 pounds (0.9 kg) of nitrogen for each 1,000 square feet. 

You know that 20 (9 kg) pounds of 26-3-13 fertilizer per 100 gallons (378.5412 ltr) equals about 5 pounds of nitrogen per 100 gallons (378.5412 ltr)  (26 percent x 20 pounds (9 kg)  = 5 pounds (18.9 ltr), with rounding).  But you want to use only 2 pounds (0.9 kg) of nitrogen per 1,000 square feet. So to apply 2 pounds (0.9kg) per 1,000 square feet, you need 40 gallons (151.4 ltr) of fertilizer. 

Now that you understand how much fertilizer you need for 1,000 square feet, you can determine how much you need for 81 square feet. Figure the ratios again:  40 gallons / 1,000 square feet = X gallons / 81 square feet 151.4 ltr/ 1,000 square feet = X ltr/ 81 square feet. 

To solve for the number of gallons (kg) per 81 square feet:  3,240 (40 x 81) / 1,000 = 3.25 gallons of fertilizer 12,080 (151.4 x 80) / 1,000 = 12.08 ltr of fertilizer Let's say it took the probe 90 seconds (1.5 minutes) to fill a 5-gallon (18.9 ltr) bucket.  5 gallons / 1.5 minutes = 3.3 gallons per minute 18.9 ltr / 1.5 minutes = 12.4 ltr per minute If you need 3.25 gallons (12.3 ltr) of fertilizer and the probe delivers 3.3 gallons (12.4 ltr) per minute, you need roughly 1 minute of  flow divided between the nine injection holes in the area to be fertilized. 

To determine how long each injection should last per hole:  60 seconds (the 1 minute of flow needed over the entire area) / 9 holes = 6.5 seconds per hole. Thus, leave the probe in each injection hole for roughly 6.5 seconds to provide 2 pounds (0.9kg) of nitrogen per 1,000 square feet.  

(Bear in mind that these are rough guidelines. Factors such as soil density, the number of probes you are using and the pressure of the system all affect these values. If these variables change, you may have to re-calibrate the probe. Unlike injecting medication into humans, varying the injection amounts by as much as 25 percent is okay.)   

Prepare the injection site Before you begin the injections, you must assess and prepare the area around the tree. Check the ground. 

Are there irrigation heads? If so, try to determine where the irrigation lines are so you do not damage them. Check for gas lines, too. If you are at a residence and you see a gas grill without a propane cylinder, a gas line may be running underground from the house to the grill, so you'll need to watch for it too.  Are flower beds planted near the tree? If so, you will need to both step carefully and watch that your hose does not drag through the flowers.  

Be aware of property lines as well. Unless you have obtained written consent from a neighbor, you can only fertilize the area of the tree that is on your clients' property. (In which case, you should fertilize at the pre-determined rate, not at an increased rate to compensate for partial fertilizing.)  

Establish the injection grid Most applicators base the injection grid on an imaginary box on the ground that encompasses the canopy edges. The injections will fall within the box at your pre-determined injection spacing.  Because the grid is something you'll likely want to simply "eyeball," it is helpful to find a visual reference point beyond the tree's dripline. 

To choose one, stand at the edge of the canopy. Pick a point that looks like it is at the edge of the canopy on the other side of your box. 

Then pick another point on a side of a building, or perhaps across the street, that is beyond the original point. By sighting both points as you move through your grid, you will be able to systematically and thoroughly cover the area to be fertilized. This technique is particularly helpful if the ground is uneven or if the area is not square.   

Begin the injections Now that you have oriented yourself in the grid box, you are ready to begin the injections:
*Stand at your starting point at the edge of the canopy. 

*Insert the probe into the soil. 

*Inject the fertilizer for the time calibrated. (In the above example, that would be roughly 6 to 7 seconds.) 

*Remove the probe. 

*Walk 3 feet (again based on the above example) to your next grid point, keeping an eye on your visual references. 

*Insert the probe into the soil and repeat the process. 

*Continue until you have reached the other side of the canopy. Step over 3 feet to begin the next row. 

*Insert the probe and repeat the process until you have covered the entire grid area beneath the canopy.  

Bear in mind that trees have many roots growing close to the trunk. So it is best to stay a foot or two away from it so that you can avoid driving the probe into the large roots close to the soil surface.  You don't always have to use a grid pattern to determine the injection area. 

For example, if you need to fertilize a conifer or other tree under whose canopy you cannot reach, the injection pattern should be circular, using about three rings. Perform the first ring of injections by reaching inside the canopy. The second ring should be at the edge of the canopy. 

The third injection ring should be about a foot or two outside the canopy.   Inspect your injections Whether you use the box or circular pattern, uniformity is important. About 2 to 4 weeks after you have fertilized the tree, tufts of greener grass should appear at each injection site. 

Your client will be able to see if your injections varied from the grid. If they have, your work will have an unprofessional look to it. Be sure to return to the site after you have fertilized a tree. Look for the tufts of grass to see whether you adhered to the grid. And observe the tree. 

Is it doing well? Does it look better or worse than before you fertilized it? As you observe, remember that fertilization is not a cure-all. Many other factors-such as soil moisture, amount of organic material, soil compaction, root damage and so on-may actually affect a tree more than fertilization. 

Tree fertilization using the liquid-injection method takes some practice. Calibrating the probe may seem complicated at first, but it does eventually become easier. Likewise, following a grid pattern by sight does become more efficient over time. The benefits to the tree are well worth the learning curve.  

Dr. Rex Bastian is director of technical services for The Care of Trees with headquarters in Wheeling, Ill., and offices serving metropolitan Washington, D.C., and New York City.  


is one of the most beneficial practices a homeowner can use for bett  er tree health. Mulches are materials placed over the soil surface to maintain moisture and improve soil conditions. 

Mulching is one of the most beneficial acts a homeowner can do for the health of a tree. However, improper mulching materials and practices may have little, or even negative, impact on the trees in your landscape.

• Helps reduce soil moisture loss through evaporation
• Helps control weed germination and growth
• Insulates soil, protecting roots from extreme summer and winter temperatures
• Can improve soil biology, aeration, structure (aggregation of soil particles), and drainage over time
• Can improve soil fertility as certain mulch types decompose
• Inhibits certain plant diseases
• Reduces the likelihood of tree damage from “weed whackers” or the dreaded “lawn mower blight”
• Gives planting beds a uniform, well-cared-for lookTrees growing in a natural forest environment have their roots anchored in a rich, well-aerated soil full of essential nutrients and soil mi­croorganisms. 

The soil is blanketed by leaves, organic materials, and living organisms that replenish and recycle nutrients. This environ­ment is optimal for root growth and mineral uptake. Urban landscapes and new developments, however, are typically harsher environ­ments with poor quality soils, reduced organic matter, and large fluctuations in soil temperature and moisture. 

Applying a 2- to 4-inch (5- to 10-cm) layer of organic mulch can mimic a more natural environment and improve plant health. Mulches are available in many forms. 

The two major types of mulch are inorganic and organic. Inorganic mulches include various types of stone, lava rock, pulverized rubber , geotextile fabrics, and other materials. Inorganic mulches do not decompose and do not need to be replenished often. 

On the other hand, they do not improve soil structure, add organic materials, or provide nutrients. 

For these reasons, most horticulturists and arborists prefer organic mulches.Organic mulches include wood chips, pine needles, hardwood and softwood bark, cocoa hulls, leaves, compost mixes, and a variety of other products usually derived from plants. Organic mulches decompose in the landscape at different rates depending on the material, climate, and soil microorganisms present. 

Those that decompose faster must be replenished more often. Because the decomposition process improves soil quality and fertility, many arborists and other landscape professionals consider that characteristic a positive one, despite the added maintenance.As beneficial as mulch is, too much can be harmful. 

The generally recommended mulching depth is 2 to 4 inches (5 to 10 cm). Un­fortunately, many landscapes are falling victim to a plague of overmulching. “Mulch volcanoes” are excessive piles of mulch materials applied around the base of trees. 

While organic mulches must be replenished over time, buildup can occur if reapplication outpaces decomposition or if new material is added simply to refresh color. 

Deep mulch can be effective in suppressing weeds and reducing main­tenance, but it often causes additional problems.

• On wet soils, deep mulch can lead to excess moisture in the root zone, which can stress the plant and cause root rot.
 • Piling mulch against the trunk or stems of plants can stress stem tissues and may lead to the development of insect and disease problems or stem girdling roots.
• Some mulches, especially those containing fresh grass clippings, can affect soil pH and may eventually lead to nutrient deficiencies or toxic buildups.
• Mulch piled high against the trunks of young trees may create habitats for rodents that chew the bark and can girdle the trees. 

• Thick blankets of fine mulch can become matted and may reduce the penetration of water and air.
• Anaerobic “sour” mulch may give off pungent odors, and the alcohols and organic acids that build up may be toxic to young plants.  The choice of mulch and the method of application can be important to the health of landscape plants. The following are some guidelines to use when applying mulch:
• Determine whether soil drainage is adequate and if there are plants that may be affected by the choice of mulch. Most commonly available mulches work well in most landscapes. Some plants may benefit from the use of slightly acidifying mulch, such as pine bark.
• For well-drained sites, apply a 2- to 4-inch (5- to 10-cm) layer of mulch (less if poorly drained). Coarse mulches can be applied slightly deeper without harm. Place mulch out to the edge of a tree’s crown or beyond. Remember, if a tree had a say in the matter, its entire root system (which usually extends well beyond the drip line) would be mulched.
• If mulch is already present, check the depth. If sufficient mulch is present, break up any matted layers and refresh the appearance with a rake. Some landscape maintenance companies spray mulch with a water-soluble, vegetable-based dye to add color to faded material. 

• If mulch is piled against the stems or tree trunks, pull it back several inches/centimeters so that the base of the trunk is exposed. Composted wood chips can make good mulch, espe­cially when they include some bark and leaves. Fresh wood chips also may be used around established trees and shrubs. Avoid using fine, non-composted wood chips, as soil nitrogen may be taken up by the roots as the wood chips decompose.