As most arborists know, one of the fundamental building blocks for healthy trees and shrubs is healthy, balanced soil. Sometimes all it takes is a quick look at the condition of a client’s trees to see that something is off. Other times, the causes of poor fruit production, stunted growth or an overall lack of vigor are more difficult to determine, in which case soil testing might be a first step toward discovering the culprit.

For the arborist just starting up a plant health care (PHC) section, the idea of identifying these problems and then initiating a successful soil-management program can be overwhelming. Thankfully, the experts we spoke with for this article say that, although they represent specific soil-amendment product lines, they are happy to field general questions from arborists who are just starting out in PHC and also can help them determine what types of products to use.

According to Tim Newell, company administrator for The Doggett Corporation, a 40-year TCIA corporate member based in Lebanon, New Jersey, the model for ideal soil conditions is found in a healthy forest environment. “In a healthy forest, you don’t need to help the plants along,” he notes. “You have healthy microbial activity on the forest floor. It’s the natural recycling of waste materials. We don’t have that in the urban forest, because we’re removing the leaves and other organic material. We find poor soil conditions there, along with things like inappropriate plant selection and improper planting techniques. All these affect the health, color and vigor of trees.”

When asked what the most important aspect of soil management is, Newell says, “It’s so multi-faceted, you can’t focus on just one thing. There are many aspects to healthy soil. Proper soil fertilization and management is one of the best things you can do for trees, but done wrong, it can be one of the most damaging. The ‘more is better’ philosophy doesn’t work in this case.”

Craig Lambert, sales representative for The Doggett Corporation, explains some of the basics of soil amendments for those just starting out. “Soils are a living media that provide biological activity,” he notes. “The use of soil amendments helps in many ways over time to enhance rooting and soil conditioning, to solubilize nutrients for plant uptake, to enhance vigor and to provide a food source for microbes.

“For example, biochar is a great amendment that has been widely used for the past several years,” Lambert continues. “Unlike charcoal, biochar is produced by a process of burning wood by-products without oxygen. It becomes very porous and helps retain moisture and nutrients in the soil. Biochar comes in several forms and is ideal for soil conditioning when backfilling after air excavation. It also works well in conjunction with composts.”

Lambert adds that, in addition to key fertility elements such as nitrogen (N), phosphorus (P) and potassium (K), certain trees may utilize micronutrients – including iron, manganese, copper and zinc – either efficiently or inefficiently. “Many of these (micronutrients) are formulated in a complete fertilizer or can be applied separately,” he notes. “Some are formulated together as a package themselves, and most are available in a chelated form that makes them readily available to the plant.”

Rob Gorden, director of urban forestry for Arborjet, Inc., a 20-year corporate member company out of Woburn, Massachusetts, covers several other suggestions for amendments that can beef up soil and increase its overall health. “One important concept that has had recent popularity is the notion of feeding soil microbes to assure healthy soil,” he explains.

“And how does one feed soil microbes? First, let’s define naturally occurring soil microbes,” Gorden continues. “They consist of decomposer organisms that break down organic matter into useable plant nutrients. These include visible arthropods and insects, such as worms and beetles, but the true workhorses go largely unnoticed, including microscopic soil-dwelling fungi, bacteria, protozoa, viruses and algae. Decomposers also contribute to improved soil structure, which reduces soil compaction and encourages root development.”

When looking to “feed” soil microbes, Gorden says there are two important components to look for in a soil additive: carbon and sugars. “There are quick- and slow-release carbon additions for healthier soils, and they are found in any number of products available to arborists,” he explains. “Humic and fulvic acids are great slow-release carbon sources and are found in certain supplements. Molasses is an unusual addition that provides both quick-release carbon and sugars, both of which are utilized rapidly by plant-friendly microorganisms. If you can identify a soil supplement that provides sugars, humic acids, carbon and other beneficial ingredients, you don’t have to make your soil enhancement very complicated.”

One other often-underutilized group of soil supplements, according to Gorden, is the plant growth regulators (PGRs). “PGRs serve as one of the best solutions for a tree under stress, or for a tree recovering from stress, pest damage or poor growing conditions,” he notes. “PGRs increase chlorophyll production, resulting in darker-appearing leaves. They increase the control exerted by ‘guard cells’ around leaf stomata, thus reducing
water-loss stress. They suppress the release of plant hormones typically identified with top growth and expansion (gibberellins), and they increase the release of abscisic acid, a chemical that increases root development and stress tolerance.”

(Click here to read Rob Gorden’s expanded report on soil enhancements and their role in a comprehensive PHC program)

A 21^st-century PHC issue

Gary Maurer, president of the Green Pro family of companies, a 28-year TCIA corporate member based in Jonestown, Pennsylvania, agrees with the concept of the forest environment being “a dynamic, self-sustaining system that is not managed by man.” He adds, “In the forest, tree roots are free to grow, unhampered by buildings, curbs and concrete. The roots can get plenty of air and water, and trees are nourished by the decomposition of their own leaves and are not subjected to all kinds of chemicals that compromise life in the soil and, in severe cases, the life of the tree. Given where and how we sometimes plant trees, it’s a testament to their resiliency that they survive at all.”

Arborists should be recreating the forest environment, to the best of their ability, as the goal of a soil-amendment plan, according to Maurer. “We consider the entire area of soil health and soil amendments to be a 21^st-century PHC issue,” he adds. “With mounting pressure from the public, environmental groups and government regulators, the tree care industry is being forced to pay more attention to what it is doing to and with the soil. So soil health is becoming more mainstream within the industry.”

He continues, “Consider how different it is with an ‘improved’ property containing houses and commercial buildings versus the forest. Most good soil is stripped off and sold. Heavy construction equipment compacts the soil and crushes soil biology. When construction is completed, the beneficial biological communities are so diminished, restricted or even eliminated that their critically important contributions to nutrient cycling and plant health are lost. In short, once removed from the forest, a tree loses much of its support network, thus becoming much more dependent on proper management for its very survival.”

Soil testing

Historically, Maurer states, tree health has focused largely on disease management and fertilization, not on soil health, despite the fact that “75-80% of PHC issues can be traced back to problems within the soil.” So the first thing he recommends is having a soil test done. “Most people don’t know there are two main types of soil tests: nutrient tests and nutrient-available tests. They use two very different testing protocols and generate two different sets of data.”

Maurer’s brother and business partner, Keith Maurer, is product designer and soil-lab director for Green Pro. He further explains the two types of testing. “Nutrient testing was designed for agriculture and field crops. A nutrient-available soil test is a better diagnostic tool for trees and shrubs. It also is better at prescribing what it will take to fix the soil and make it work better, both biologically and chemically. It replicates the same method the tree uses to ask for nutrients.

“The chemical process of nutrient extraction is totally different, relying on weak acids instead of strong acids. Whereas a strong acid test might indicate there is enough phosphorous in the soil, a weak acid test might indicate that phosphorous is lacking and must be added. In other words, even though the phosphorous is present in the soil, it is not available to the tree for any number of reasons.”

Patrick Anderson, arborologist for Rainbow Treecare Scientific Advancements in Minnetonka, Minnesota, adds his own take on soil tests and their importance to tree care. “Soil management is one of the best things you can offer your clients,” he says. “It can be a great opportunity. If someone calls for a pruning, they obviously care about that tree, so fertilizing it can be an easy sell.

“It might start with taking a soil sample for analysis,” he adds. “If you’re seeing any abnormal leaf color and stunted leaf or twig growth, you’ll want to test the soil. A lot of state university ag programs will run soil tests and report to you what nutrients you’re missing and what amount of fertilizer to apply, usually per 1,000 square feet. The report also will show the pH level and organic-matter content of the soil.

“I would recommend taking a good number of soil samples from around your service area,” Anderson continues. “In general, you’ll find trends of what soils are in your service area, and that will dictate the products you’ll want to use. You might even want to follow up a year later (with another soil test) to see how you’re doing.”

Types of soils

According to Keith Maurer, healthy soil is “loose and friable, with lots of open space for oxygen and water to get to the roots, plenty of organic matter and all of the critical biology that helps transport nutrients to the tree and provides a level of protection against certain soil diseases.” Different soil amendments will be needed depending on the type of soil you’re dealing with, which can vary regionally and even site to site.

Keith Maurer describes the following soils:

• “Clay is not the best soil to grow things in, although it can be rich in nutrients. Clay is made up of heavier atomic structures on the Periodic Chart that are attracted to each other like a magnet. Because they bind so tightly to one another, there is little room for oxygen and water to get into the soil and to the roots. The soil does not hold much water since most of it runs off. Breaking this attraction requires the intervention of substances that reduce the magnetic attraction between particles or enable nutrients to squeeze through the microscopic spaces between particles.”
• “Sandy soils have their own challenges, specifically the inability to hold on to nutrients. This often causes the symptoms of chloroses or other nutrient deficiencies to be exhibited. Sandy soils also make it difficult for biological systems to survive or thrive, causing additional problems. Taking steps to increase the organic-matter content of sandy soils is the best corrective action that can be taken. The organic matter acts like a sponge to hold moisture and nutrients from leaching out while providing food sources for the critical biological communities. Organic acids that chelate (hold onto) nutrients also help.”
• “Silty soils have properties of both clay and sand. They have a slimy feel, yet are gritty at the same time. The chemical bonds are not as strong as clay soils, but they have better porosity. However, nutrients and water do not leach through as fast as in sandy soil.”

He adds that most soils are a combination of all three types: sand, silt and clay. “An ideal soil would contain equal parts of all three, with 10% by volume of organic material. Such a soil would have the ability to hold nutrients and water, support critical biological communities and contain the oxygen required by all living systems, including the roots.”

The proper equipment

“The first thing you need (when starting a soil-management program) is to start with good equipment that can handle good agitation,” says Tim Newell, “whether paddle or jet agitation that can handle powder or liquids and solubles. Agitation is very important, so get the best equipment you can.”

Craig Lambert agrees. “Some products require good agitation to be effective. When mixed correctly, they become a water-soluble suspension that feeds continuously for six to nine months and mimics the forest floor.”

Rob Gorden adds to the equipment list. “Rather than guessing at soil conditions, there are several tools a new PHC practitioner might use to help them. The first is a simple soil probe,” he notes. “It can identify compaction, depth of soil, condition of the soil and even anaerobic conditions caused by sitting ground water, which forces oxygen out, causing roots to die.

“There are even mechanical methods that can rapidly change soil conditions around a struggling plant without injury to its sensitive roots,” Gorden adds. “The Supersonic Air Knife is one such tool, a device that uses high-velocity air directed into the soil to break it up. After the use of such a tool, nutritional supplements are often added to improve soil structure or enhance microbial activity. The simplest addition may be the use of composted, decaying plant matter.”

Patrick Anderson puts dollars and cents to the equipment someone might want to acquire when just starting out in PHC. “You could start with something as simple as a $50 spreader with a granular, surface soil amendment,” he notes. “The main issue with granular is that some products can be interrupted by really healthy turf or by runoff from a deluge. Or, you could do a liquid deep-root injection with a probe that creates a spaced pattern along the drip line of the tree. For that, you’d want to start with a tank that holds at least 200 gallons and applies the liquid at about 200 psi. You’re looking at about $5,000 for that setup in the low to medium range.”

Anderson adds, “Basically, you’re putting these nutrients down into the soil to be taken up by the tree. This is maintenance fertilization, where you’re going back on a regular basis. Then there’s soil modification, which actually changes the physical nature of the soil with amendments like compost and biochar. For that, you can get a $2,000 AirSpade or similar air-injection tool for breaking up compacted soils to add the compost or biochar. Then you’ll also need an air compressor, which can be rented for around $200 a day or purchased used for about $5,000. You have to decide what is most important in your area and what treatments you want to focus on.”

Newell summarizes the importance of healthy soil for the life and vigor of a tree like this: “You can only cut a tree down once, but you can maintain that tree for a lifetime.”

Gorden adds his own wisdom. “Delving into PHC lets a company explore the potential to be tree physicians rather than just tree morticians,” he says. “PHC is not just about controlling visible pests and diseases. It’s also about providing optimal growing conditions for the trees in your care. This often can be achieved by improving soil health and encouraging microbial survival and microbial growth.”