Can Disturbed Soils Grow Healthy Landscapes?

Are you landscaping a recently constructed setting, only to find the site defies your intent? Soils having gone through construction and site development may be referred to as disturbed soils. Construction impact can be expected unless landscape recovery is well planned and executed.

Healthy soil is the arena where microorganisms and plant roots inhabit a dynamic soil matrix of organic and mineral particles, mixed with water and air. Soil texture is the ratio of large sand particles, middle sized silt, and very fine clay particles in soil. Texture affects water percolation and retention, aeration, and nutrient availability. In natural soil matrices, the underlying eroding bedrock provides most soil components.

Particles of sand, silt, and clay aggregate into clumps or sheets making up soil structure. Structure determines the amount, size, and arrangement of pore space amongst soil particles allowing for water, air, and biota. Soils favoring plant growth contain about 45% mineral particles, 50% pore space, and 5% organic matter by weight. Porous aggregates provide an important nutrient and water reservoir and aggregate stability protects organic particles residing within against microbial consumption.

Aggregate soil structure develops naturally over a very long time and eventually grades into horizons of leaching and erosion. Typical site preparation for construction of load-bearing building foundations and other structures strips any organic surface and mineral topsoil layer, then grades the subsoil or digs to the parent material. As a result, soil horizons are often destroyed.

Because of grading, equipment movement, and perhaps waste disposal, disturbed soils can be highly altered. Soil moving, mixing, and removal disrupts interrelationships that landscape plants depend on. Organic layers and soils are missing, leaving densified, compacted, and mostly clay-rich soils. Compaction of soils left in place starts at the surface and deepens with continued traffic. Macropores are compressed more thoroughly than fine pores. This crushing effect leads to poor water infiltration and drainage making it more difficult for plant roots to grow and reduces habitat for large- and micro-organisms within.

This existing treed landscape has been excavated to complete the adjacent apartment parking and driveway. In addition to soil disturbance, mature tree roots were lost as the topsoil layers were graded. Photo: Scott Sjolander, Penn State Extension.

One may begin to remedy disturbed soil conditions and initiate natural processes following these steps:

1. Seek the advice of an expert and do not rely on rules of thumb.
2. Consider replacing poor or contaminated soil with a high-quality topsoil or engineered blend.
3. Loosely breakup existing compacted soil having good component conditions.
4. Carefully cultivate entire planting areas with composted organic material. Too little organic material omits soil moisture reserve space and living space for in-dwelling organisms. On the other hand, excessive organic matter can create sodden water-holding conditions inhibiting biotic function.
5. Choose plant materials that are tolerant of compaction, drought, poor aeration, and low fertility.

When preparing spaces, excavating or moving fertile soils, do not smash those soils that you are going to replace. This will help conserve existing structure in soil you might need and use later. Keeping the trucks and loaders outside the planting zone when fluffing, mulching or doing other work will help preserve soil matrix and biotic functions. This will pay off in quicker and better success with a new landscape on disturbed soil.

References

Bell,Terrence; Kristy Borelli; Sarah Isbell; Suzanne Fleishman; Laura Kaminsky; Mara Cloutier. 2021. Understanding and Managing Soil Microbes. Penn State Extension.

Barbercheck, Mary. Many Factors Influence Interpretation of Soil Health Tests. 2020. Penn State Extension.

Elmendorf, William. Understanding Tree Planting in Construction-Damaged Soils. 2017. Penn State Extension.

Summon, Datta; Saleh Taghvaeian; and Jacob Stivers. 2017. Understanding Soil Water Content and Thresholds for Irrigation Management. Oklahoma State University.

White, Charles and Mary Barbercheck. 2017. Managing Soil Health: Concepts and Practices. Penn State Extension.