Protect roots while working

Photo Courtesy of Supersonic Air Knife.

Exposing tree roots with an air excavation tool makes it easy to prune them or check for disease without injuring the tree.

There is one great reason to use an air excavation tool, Robert Wagoner says. That is to protect the roots of a tree while excavating around it because there is no physical damage. From that reason, many other subordinate reasons develop.

Wagoner is owner of Branch Out, a tree service and landscape company in Pasadena, Calif., and he purchased an air knife for a job that he was hired to do. A homeowner’s prized Australian bottle tree fell over in a windstorm and he wanted Wagoner to save it. The ISA-certified arborist knew there was little hope for the tree if he had to hack its remaining roots from the soil with a pick and shovel, so he bought an air knife.

An air excavation tool works by funneling compressed air through a pipe and using it to blow dirt out of the ground. Wagoner used it to excavate and expose the roots of the bottle tree, which was subsequently found to have girdling roots that had damaged it severely. He was able to cut away the girdling roots, replant the tree and cable it. Last he knew, the rare tree was still alive and doing well.

He has since worked on several projects using the tool.

Wagoner used the air knife to expose the roots of a sycamore tree that had raised the patio concrete behind a house, and prune back the ones that were causing the damage. Then he dug an 18-inch trench with the air knife to install a root barrier between the tree and the patio to prevent future intrusions.

He was also able to excavate the roots of a tree thought to be shifting and cracking the floor of a commercial building. Wagoner found that they weren’t going under the foundation at all, and was able to do this work without damaging the tree roots or destroying evidence for the insurance company.

A homeowner wanted to install a spa in the middle of a large oak tree’s rootzone, and the city specified that an air excavation tool be used to move the roots without damaging the tree. Wagoner was able to excavate the entire hole for the spa, and also dig the trench for the water and power line without cutting roots.

Wagoner points out that an air tool like this will cut through dirt, sand and clay in much less time than men using pick and shovel can do. By blowing dirt from around the roots under high pressure, it can dig a hole, extract dirt from around roots or supply lines, or even dig a long trench. On one job, he excavated a trench 1 foot wide, 2 feet deep and 40 feet long in two hours, by himself, and did it close to a building where there were tree roots. Even hard-packed clay will loosen up and come out in layers, he says, and it will not injure even small feeder roots.

Photos by Don Dale.
Robert Wagoner demonstrates how the air knife is easily assembled.

Branch Out is a company that does general landscape contracting and maintenance, as well as tree planting and pruning. Wagoner bought the company 15 years ago after a previous career as a teacher and scientific editor. With 10 employees, he does a wide range of work from contracting tree plantings with the city of Pasadena and the Pasadena Beautiful Foundation to doing lawn maintenance. Compressed air excavation work is one of those specialized areas that gives his company a boost because not many companies offer the service.

“If you’ve got to cut through a rootzone, use an air knife. End of discussion,” he says. He had one job where a trenching contractor came in and dug a deep line within 3 feet of a large Deodar cedar, and the sight was sickening. The same job could have been done with a compressed air tool without any damage to the tree’s roots, with irrigation or electric lines run among and under the tree’s roots.

Another use for the tool is to expose tree crowns in order to look for the prevalence of armillaria or other root diseases. Wagoner, who is not a disease diagnostician, points out that this would be a great alternative to digging around a diseased tree with sharp hand tools. Root pruning also becomes much easier when an air tool is used to expose all roots.

“Just make sure you wear good protective clothing,” Wagoner says. Coveralls, a hard hat, face guard and gloves are necessary when there’s this much dust and debris flying around. In addition, the aluminum tubing (other such tools come in brass or stainless steel) gets too hot to handle because of heat from the compressor. A guard at the bottom of the tube prevents most debris from flying straight upward. Surprisingly, he says, the excavated dirt doesn’t go far and isn’t difficult to recover and use as backfill. It is a great labor saver, but obviously, it becomes less effective in soil that is very rocky.

Photos by Don Dale.
The air knife is controlled by a trigger, and an air gauge tells when proper air pressure is reached. A guard at the bottom of the tube helps prevent injury from debris, but protective clothing is still needed during operation.

He owns a Supersonic Air Knife, Easy Green Tornado Model X-LT. This company has several models (, and they are basically an aluminum tube with a pressure gauge, an air hookup and a trigger, with a nozzle at the bottom end to restrict airflow. Another company that makes a similar tool is the Air-Spade by Concept Engineering Group (

Photos by Don Dale.
Digging around the roots of this camphor tree would be damaging without an air excavation tool.

These tools, Wagoner notes, require very high air pressure. The Air Knife X-LT model, for example, requires 100 PSI and 125 CFM. The X-HFA model requires 100 PSI and up to 375 CFM of compressed air. This demands a high-volume, tow-behind compressor, which Wagoner rents whenever he has a job requiring the tool.

Bishop Supply, in Whittier, Calif., carries the Supersonic Air Knife, but General Manager Doug Wright says he only sells one or two a year. He says it’s a tool that does a lot of good, but it hasn’t become widely known yet.

“It’s a newer field that not a lot of arborists have specialized in,” Wright says, noting that a vacuum attachment is available that reduces dust.

For Wagoner, the tool, very simply, is good for trees—and for arborists.

“I know if I do good work I’ll be able to retain the reputation I’ve built,” he says, and that boosts the profitability of a company that gets a lot of its work from referrals.

Don Dale is a freelance writer and a frequent contributor. He resides in Altadena, Calif.