Tips for Developers and Landscapers
Soil health is important in landscaping because poor soil will not grow anything, including ornamental plants and trees. Erosion, overuse, and compaction are just some of the problems that lead to poor soil health.
What Is Soil Health?
Soil health is the capacity of the soil to produce fiber, food, and fuel. Since one inch of topsoil takes 500-1,000 years to produce, soil is not a renewable resource. Urban areas are a special challenge because construction disturbs or removes the topsoil. The soil left does not support much life.
Soil is not the same as dirt. Dirt is the rather sterile medium that is left behind when the topsoil is removed. Soil is a rich web of interconnected animals and plants, much of them microscopic. Plants depend on this web of life to grow. For example, microorganisms digest dead plant material, returning the nutrients to the soil. Earthworms move soil around and aerate the soil so air and water can penetrate it. Moles and other small animals eat the earthworms while breaking up clay or other hard soil, and so on.
Soil Properties
Soil properties fall into two categories, those we can change and those we cannot change.
Inherent
Inherent soil properties take thousands of years to change. Nothing humans do will change these properties over the course of a year. Inherent soil properties include soil type, depth to bedrock, and amount of clay in the soil.
Dynamic
Dynamic soil properties are chemical, biological, and physical properties that land management and cultivation practices can change. They include soil organic matter, soil structure, biological activity, water-holding capacity, nutrient concentrations and bulk density.
Increasing Soil Health
Adding organic matter to the soil will almost always improve soil health. There are five major principles to keep in mind when working to improve soil health: disturb the soil as little as possible, keep the soil covered as much as possible, grow something in the soil as much of the year as possible, promote biodiversity in the soil and above the soil, and integrate livestock if possible. The last one doesn’t happen much in an urban setting, so won’t be addressed here.
Do Not Disturb
Tilling the soil before planting is routine for vegetable growers. Some landscape beds are also tilled before the initial planting. Tilling the soil disturbs the mycorrhizae. Mycorrhizae are beneficial organisms that form a net throughout the soil. Plants, especially trees, are connected to one another through this net and use it to communicate. Tilling tears the net and breaks off communication between the plants there.
Tilling also collapses the soil structure, so water and air have a hard time penetrating it. Greenhouse gases are released during the tilling process. Wind and water are able to erode a tilled surface more than untilled ground.
Instead of tilling, use targeted holes to plant perennials, trees, and shrubs. Leave the soil between plants untilled, if possible.
Tuck The Soil In
Bare soil is easily whisked away by wind and rain. Keeping the soil covered as much of the year as possible is important for erosion control. Depending on the season and the desired plants, that cover may be mulch, ornamental plants, or plants grown specifically to provide a cover.
We sell several ground covers that can act to keep the soil where it belongs. Partridge berry is a small vine that acts as a ground cover in the shade. The green leaves are drop shaped and the red berries are favored by birds. Periwinkle is another ground cover that likes shade. The purple flowers look nice around a tree. Creeping buttercup has bright yellow flowers and grows in meadows and other areas getting direct sun.
Cover Crops
While mulch will cover the soil and help stop erosion, it doesn’t feed the microbes in the soil the way living plants do. Using a ground cover as a living mulch keeps the microbes fed and the soil fertile. Healthy microbes will improve the success of ornamental plants. The roots also hold the soil, making it more stable and more resistant to water and wind erosion.
When planting a cover crop, choose one that grows in your area and is a legume. Legumes have beneficial bacteria in the roots that take nitrogen from the air and change it to something plants can use. The legume uses what it needs but excretes the excess into the soil for other plants to use. Clover is a common legume to use as a cover crop
Promote Biodiversity
Promoting biodiversity above ground promotes it below ground. Planting a mixture of perennials, trees, and shrubs supports more insects and other beneficial wildlife. It also looks better than a monoculture.
Below ground, each plant deposits excess food and water into the soil. Microbes feed on these nutrients. Each different plant deposits a different mix of nutrients. Having many different types of plants growing makes sure that many different nutrients are available in the soil. In addition, it means that one disease or pest won’t destroy the entire plant grouping because most diseases and pests are host specific.
Measuring Soil Health
Soil health can be measured by testing a sample of the soil for nutrients, pH, soil type, and microbes in the soil. In the United States, each state has a soil lab that performs these tests for consumers for a nominal fee. In addition, if you specify the type of plants you will be growing in the soil, the soil report you receive will include recommendations for fertilizing and adjusting pH that are optimized for those plants.
Each landscape bed or area will need its own soil test. Make sure you keep a list of which sample is from which area because the sample reports will come back labeled “sample 1, sample 2, etc.” You don’t want to have to guess which sample is which. Soil tests are recommended every three years unless you are having a specific problem in an area. Sometimes an area just doesn’t grow anything, and you want to test more frequently to see if your remedies are working.
Adding Organic Matter
Organic matter is key to soil health. Adding an inch of compost to your landscape every spring will add organic matter and improve soil health. In mulched landscape beds, that is as simple as adding an additional inch of mulch each spring. Mulch generally decomposes an inch a year. Three inches of mulch reduces weeds, stabilizes soil temperature and moisture, and protects the plants from soil borne diseases. Adding another inch of mulch each spring maintains the three-inch depth and adds organic matter to the soil. For lawns, rake the mulch in with a leaf rake to help it contact the soil.
Questions?
At Garden Plants Nursery, our staff can answer most gardening questions. If you need help understanding a soil test or finding the perfect plant for your soil, give us a call at 931.692.7325.
