Healthy Trees Need Healthy Soil: A Practical Guide for Mountain Properties

When a tree declines, fertilizer is often the first solution people consider. On many developed mountain properties, however, the more important problem is the physical condition of the soil: compaction, drainage disruption, buried root collars, construction fill, or loss of the organic surface layer.

Forest soil is a living structure

Undisturbed forest soil contains mineral particles, pore space, roots, fungi, bacteria, organic matter, and decomposing litter. Together they regulate water, oxygen, nutrient cycling, and root growth. A landscaped soil can look dark and fertile while still functioning poorly if it is compacted or poorly drained.

Root collars should not be buried

The base of the trunk should transition visibly into the main structural roots. Mulch volcanoes, fill soil, sediment, or landscape installations can bury this transition. Chronic burial can hold moisture against bark, encourage adventitious roots, restrict oxygen, and conceal girdling roots or decay.

Water problems are often soil problems

Trees can suffer from both drought and excess water on the same property. Compacted clay may shed rainfall at the surface while remaining saturated in lower areas. Concentrated runoff from roofs, roads, or grading can also change soil moisture patterns around established roots.

Mulch should imitate the forest floor

A broad layer of natural arborist wood chips or hardwood mulch can moderate soil temperature, reduce evaporation, protect the surface from traffic, and add organic matter as it decomposes. Keep mulch away from direct contact with the trunk and prioritize width over excessive depth.

Aeration has to match the problem

Air excavation and targeted soil decompaction can be useful where compaction or buried root collars are documented. The goal is not to aggressively till a root zone, but to improve soil structure while minimizing root injury. Treatments should be based on actual site conditions rather than applied automatically.

Soil restoration is long-term tree care

For mature trees, improving the rooting environment can be more valuable than repeatedly treating canopy symptoms. Protect the soil from traffic, restore organic cover, correct drainage problems carefully, expose buried root collars when needed, and preserve as much undisturbed rooting area as possible.

Healthy trees are built from the ground up. On a mountain site, the most effective arboricultural work often begins by understanding how water, roots, soil structure, and topography interact.

Research context

Research on urban soils shows why repeated canopy treatments cannot compensate for a chronically poor rooting environment. Compaction can physically restrict root penetration, while organic surface treatments can improve soil properties over time. On mountain properties, those effects interact with slope, shallow soils, runoff concentration, and localized saturation, making site-specific soil and water assessment particularly important.

Sources and further reading

Grabosky, J. & Bassuk, N. (1995). A New Urban Tree Soil to Safely Increase Rooting Volumes Under Sidewalks. Journal of Arboriculture 21(4):187–201. doi:10.48044/jauf.1995.030.

Scharenbroch, B.C. & Watson, G.W. (2014). Wood Chips and Compost Improve Soil Quality and Increase Growth of Acer rubrum and Betula nigra in Compacted Urban Soil. Arboriculture & Urban Forestry 40(6):319–331. doi:10.48044/jauf.2014.030.