Enhancing Your Soil

soil in hand

Soil Building: How it Helps the Environment and Your Wallet

Here in the Pacific Northwest, it is easy to get lost in the beauty of the landscape. The trees and forests that we admire so much are there thanks to rich soil that makes the shrubbery healthy and strong. So why do people have to work so hard and spend so much money on constructed landscape environments to achieve the same effect? It is because there is too much focus on the beauty of the plants and not enough on the foundation. Here are some tips on how to keep soil healthy and the landscape beautiful.

Shallow Development for Soil is an Issue

Since soil is the foundation for any site in landscaping, it is important to understand how to set it up to create a healthy landscape. Built environment usually has very shallow, biologically inactive, manufactured topsoil layered over compacted fill. The interface between these layers is distinct and prevents deep rooting and free drainage for water. These soils do not allow the water to be fully absorbed before saturating what is underneath, which is not optimal for plants trying to grow from that soil. To thrive, plants need equal amounts of air and water in their root zones. An excess of water can lead to asphyxiation of roots and increase the potential for compaction or erosion of soil structure.

Natural soils have biologically active flora and fauna that feed on forest litter and produce exudates and nutrients. These exudates and nutrients feed plant material and enhance healthy soil structure.  While manufactured soils are usually biologically inactive and thus require heavy amounts of plant-available nutrition from fertilizer. Landscapers use synthetic fertilizer because it can be engineered to release over a long period, which produces product and labor costs. However, synthetic fertilizers bypass the natural degradation process that feeds soil microorganisms and therefore do not promote their development. By skipping the degradation process, the soil microorganisms become severely dehydrated due to the salts and sulfur in the soil.

A Deeply Rooted Problem

It is best to address shallow soil issues during construction. Most municipalities are changing their building codes to enforce developers to remove, stockpile, and properly install biologically active native soils on new sites. This will develop deeper soil profiles to prevent interface problems. For more information on this building code, please see City of Seattle, Client Assistance Memo 531.

Since these standards are relatively new and are not universally applied to all jurisdictions, most are left with unnecessary long-term maintenance expenses. Wholesale renovation of existing landscapes afflicted by shallow soil issues can be successful, but costly. If the issue is left alone, most landscape contractors treat the symptoms of the problem (poor plant health, plant mortality, and drainage issues) perpetually. To prevent this, partner with the landscape contractor to treat the cause.

Addressing the Issue with the Landscape Contractor

If the landscape contractor is confused when asked for help in treating the cause of the soil problems, hire a more knowledgeable contractor. This may cost a bit more, but a strong partnership can add asset value, reduce risk on the property, and save money in the long term.

Shallow Soil Solutions

A soil core test or digging a small test hole can tell a lot about the location and severity of the topsoil-subsoil interface and their textural qualities. Shallow interfaces have “perched” water tables, which can be improved through aeration in combination with adding soil amendments (also known as topdressing). Aeration breads up compaction, increases rooting depth, and aids water infiltration. Topdressing after aeration allows for subtle changes in soil texture, an addition of organic content when necessary, and an introduction of soil flora and fauna. When aeration and topdressing become part of a regular maintenance regime, a significant impact will take place over time.

Sustainable maintenance practices that rely on organic fertilizer, pH management, prescriptive use of pesticides under an IPM program, and carefully managed irrigation practices can create a balance that resembles a natural system. When this happens, the landscape will require less supplemental fertilizer, water, and pesticide usage, which makes these strategies economically feasible and environmentally sound.