Roots and the Pneumatic Soil-Excavation Tool

Girdling roots grow around the trunk rather than away from the trunk, potentially strangling the tree. Use of a pneumatic soil-excavating tool make root inspection easy. Photo courtesy of the author.

I consider roots to be the most critical part of any tree, shrub or plant. Without healthy roots, a plant will not perform. I have noticed that the more vibrant the plant is below the ground, the more vibrant the plant will be above ground. Two important functions of the root system are to anchor the plant so it stays in position and to help move water and nutrients to all parts of the plant.

In the world of arboriculture, where we regularly work with woody plants, I have observed that any issues with the roots can potentially cause poor health. A weak root system means a weakened plant, both structurally and biologically. This weakened root system can also predispose the plant to other problems such as tree failure, attack from insects and diseases or being less tolerant of stress from drought and temperature extremes.

Trees growing in the forest generally aren’t exposed to root problems caused by people. Nutrient recycling (decomposing leaves, twigs and other organic matter) keeps forest soils healthy by allowing adequate amounts of air/water exchange with the root systems. But what are ways a root system in a landscape can become compromised? I have noticed two common types of root problems. One is caused by people, the other is more naturally occurring.

People damage roots all the time. This is a common root problem in urban settings where people compact soils around the root zone. Continually walking over the root zone, such as in a park, or cars parking under trees, for example, will eventually compress the soil enough that it will damage the fragile feeder roots. These tiny feeder roots are generally found within the top 8 inches of soil, and their primary function is for moving water and nutrients from the soil into and throughout the tree.

Root systems also can be damaged without human intervention. Roots can grow around the trunk rather than away from the trunk, potentially strangling the tree. This is referred to as a girdling root. When the root flare (the widening of the base of the tree that is the transition area from the trunk to the roots) is not visible, I suspect a girdling root. As the tree continues to grow and mature, roots grow as well. The root begins to girdle the tree and restricts the cambial tissue, which is the plumbing of the tree. A function of this cambial tissue is to move water and nutrients to all parts of the tree.

The symptoms of a tree with root problems are often easy to detect. Symptoms could include a thinning canopy, dieback from the top or thinning isolated to one side. When I observe a tree looking this way, my first action is to inspect the root flare. But how do we inspect roots so we can begin to correct these problems that might be affecting their health?

My tool of choice is the pneumatic soil-excavating tool – an air compressor forcing air through a wand attached to a hose. This can be used to loosen soil throughout the root zone or to remove mulch/soil from around the base of the tree. Amazingly, the force of the air does not damage the roots. Even though the air is traveling through the wand with amazing force and speed – commonly around 90 PSI, displacing 170 cfm (cubic feet per minute) at speeds of 900-plus mph – the roots of the plants are largely unharmed.

A pneumatic soil-excavating tool can be used to loosen soil throughout the root zone or to remove mulch/soil from around the base of the tree. Photo courtesy of the author.

There are different techniques for using a pneumatic soil-excavating tool. For trunk/root-related issues such as girdling roots, soil and/or mulch are removed from around the base to expose the root flare, allowing us to better examine this part of the tree.

For compaction issues, there are two common techniques I use. The first is to use the tool to go vertically 8-plus inches into the ground, spacing the injection sites every 12 inches, give or take. When this is used on a lawn, there is generally very little evidence on the turf of these holes. Another common method is to excavate the entire area under the dripline, excavating 6-plus inches of soil. This generally is done in an area that will be reseeded with grass or an area to be turned into a mulch bed.

David Bailey with Piscataqua Landscaping & Tree Service exposes roots using a pneumatic soil-excavating tool. Photo courtesy of the author.

The pneumatic air-excavating tool has many tree-related applications. It is very effective for transplanting or moving plants. The tool can dig a plant by blowing soil away from the roots, creating a bare-root transplant. This has been used for small shrubs as well as large trees. We also have used this tool for root pruning of trees in preparation for nearby construction. Trees on construction sites traditionally have had their roots “pruned” via an excavator. Pruning the roots by hand will allow them to heal properly, greatly increasing a tree’s rate of survival.

Girdling roots exposed. As the tree continues to grow and mature, roots grow as well. The root begins to girdle the tree and restricts the cambial tissue, which is the plumbing of the tree. Photo courtesy of the author.

The pneumatic air-excavating tool is a useful piece of equipment in the plant health care toolbox. In woody plants, a lot goes on underground that we cannot see. This tool allows us to further explore and remediate root issues, which will inevitably improve overall plant health.

The pneumatic air-excavating tool is a useful piece of equipment in the plant health care toolbox. In woody plants, a lot goes on underground that we cannot see. Photo courtesy of the author.

Chris Kemp, ISA Certified Arborist and Tree Risk Assessment Qualification (TRAQ) credentialed, is plant health care manager for Piscataqua Landscaping & Tree Service, a 10-year TCIA member company based in Eliot, Maine. A member of the American Society of Consulting Arborists (ASCA) and the Maine and New Hampshire arborist associations, he has a master’s degree in urban forestry and bachelor’s degrees in horticulture and economics, and has been involved in tree care for 30 years. Although he holds supervisory/master pesticide licenses in New Hampshire and Maine, he uses many alternative controls to improve plant health.

To view a video about pneumatic air-excavating, go to the digital version of this article online, at tcia.org/publications, and click here.

Video courtesy of Chris Kemp

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