Loosening Compacted Soil Around National Cemetery Trees With an Air Spade

Why trees need help

Trees can be an important part of a national cemetery's historic design: they give the commemorative landscape a sense of enclosure and protection, and mature trees offer shelter for gathering or resting.

A tree's health starts at its base. Repeated foot or equipment traffic wears the ground and compacts the soil, shrinking the pore spaces that let air and water move. Around a tree's roots, that weakens the roots and can harm the whole tree — dieback in the canopy can be a sign of compaction below.

Cutting a trench outward from a tree to relieve compaction around its roots. NPS photo.

The air-powered excavation spade

In several national cemeteries, Park Service staff use an air-powered excavation spade to loosen compacted soil without damaging the roots, so water and air move more freely and soil amendments are easier to mix in.

The tool: a nozzle on a fiberglass barrel with a control handle and pressure gauge, fed by a hose from a tow-behind compressor. The nozzle fires a narrow jet of air at 1,200 miles per hour. It is used two ways:

• Radial trenching — cutting trenches in the critical root zone under the canopy, running outward from the trunk. The operator holds the nozzle just above the soil at a 45 degree angle and clears 1 to 2 feet of surface a second.
• Vertical mulching — boreholes around the tree's base, made by plunging the nozzle into the soil with the trigger held down.

Air-spading a root zone in the national cemetery at Little Bighorn Battlefield National Monument. Soaking the soil first helps keep it in place and cuts dust. NPS photo.

Protective equipment shields workers, visitors and the tree. The nearby parking lot makes this a high-traffic spot. NPS photo.

The air spade at work around a tree in the national cemetery at Little Bighorn Battlefield National Monument. NPS film.

Finishing the job

• As with any digging in a national cemetery, archeologists are consulted and monitor the work.
• The trenches or holes are refilled with the excavated soil mixed with compost or sand.
• Mulch is spread around the base of the tree to add nutrients and guard against further compaction.

Radial trenches let air, water and nutrients reach the roots. NPS photo.

Mulch spread around the trees after aeration. NPS photo.

Watch: Soil Excavation and Aeration in NPS Cultural Landscapes — an air spade at work at Little Bighorn, with an archeologist monitoring.

Part of a larger effort: the National Cemetery Investment Initiative is a multiyear plan to preserve the 14 national cemeteries the Park Service manages, through repairs, training, hiring, youth partnerships and specialized equipment.

Sources

Based on "Relieving Compaction around Tree Roots," National Park Service; a work of the United States government in the public domain. The source first calls the two methods "vertical trenching or radial mulching" and then describes radial trenching and vertical mulching; this page follows the descriptions. The Park Service's film, lost when the page was imported, is restored from its page (2026-09-27).