Root-Collar Excavation: Don’t Blow It

TCI Magazine was on site in Smithfield, Rhode Island, in October 2022 to capture a root-collar excavation performed by Stanley Tree Service Inc., a dual-accredited, 33-year TCIA member company based in Smithfield. Jarod Shaw and Will Wolf were there to excavate the roots of a Bradford pear tree, which had been the victim of mulch mounding for some time and was not in the best shape.

The initial objective was to use a pneumatic air tool to remove the excess mulch and soil from around the base of the tree. The ultimate objective was to then examine the root zone for problems, such as girdling roots, and address any issues found.

Soil excavation can be used to encourage fibrous root growth outward, toward the dripline, rather than circling near or around the trunk. When they are given an opportunity to grow into mulch mounds at the base of the tree, they will take advantage of that easily available food source and not grow out into the root zone under the entire canopy. This can cause problems later on with structure, support and water-absorption capabilities.

Wolf used a steel rake to pull excess mulch away from the trunk. He uncovered some delicate fibrous roots and was careful not to tear at them. Shaw shoveled excess mulch and soil into a wheelbarrow so that when he started to excavate, the material wouldn’t fly all over the lawn.

Using a pneumatic air tool to remove soil can be very messy. There usually are a lot of soil particles flying around, so you’ll probably want to cover up the best you can. Shaw wears coveralls and gloves as well as head, eye, face and hearing protection, as required by the ANSI Z133 safety standard.

The air tool funnels air from a compressor through a hose and out a nozzle. The air pressure coming out of the compressor is about 300 psi. It is forced out of the nozzle at about 3,000 psi. The jet of air opens up into a good cutting cone of air that will move soil particles but not damage roots.

Shaw worked in radial lines over the soil surface, making a wagon-wheel shape. He made troughs in the soil, then cut the soil between them in half, and then in half again. He continued to divide the soil surface into smaller portions until the root zone had been exposed from the trunk to about 3 feet out.

The idea was to expose some of the root flare of the trunk without excavating the entire root zone. This was a good way to examine what might be going on under the soil to determine if there are girdling roots or other problems to correct. Removing excess mulch is a good start to encouraging the larger feeder roots to function better.

Shaw continued to excavate the rest of the pit, searching for any additional feeder roots that might be lingering where the mulch was piled. Wolf used root-pruning tools to remove many of the unsuitable roots that had been exposed.

Once the roots and root flare had been uncovered to the right depth, the excess soil was backfilled to the lower grade that just covered the top lateral roots. The project was finished off with 2 to 3 inches of composted woodchip mulch over the excavated area, being careful not to cover the base of the tree.

Using high-pressure air to break up and move soil around the root zone not only allows arborists to “see underground,” but also addresses compacted soil by expanding pore space in the soil to encourage air and water movement that is critical for fine roots. This soil conditioning is beneficial for growth of the roots, which in turn feed and support the tree.

Tchukki Andersen, BCMA, CTSP, is staff arborist for the Tree Care Industry Association.

Jarod Shaw is a crew leader, and Will Wolf is employee development and training lead ; both are with Stanley Tree Service Inc., based in Smithfield, R.I.

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