Written by Myra Klockenbrink
Fourth in Greenwich Sustainability Committee’s One Land Series on Biodiversity
When we look out over our lawns and gardens, the one thing we don’t see is the soil beneath the living landscape. Healthy soil underpins the health of our environment. Much like the millions of microorganisms inside the human biome, soil is the microbiome of the above-ground world. It is crucial to mitigating the effects of climate change, for building resilience in the landscape and for sequestering carbon.
Soil Moderates the Effects of Climate Change
Most of us have lawn, garden beds, trees, maybe a wetland area and all of them are very dependent on the health of the soil. Healthy, living soil absorbs and holds water like a sponge. The deeper the living soil in the ground, the more water it can hold over longer stretches of time, creating a cushion against periods of drought and helping plants stay healthy. The more plants that are supported, the more carbon they can draw down from the atmosphere. Absorbent soil will slow run-off from large rain events, filter out toxins from that runoff and keep them out of the water supply. And living soil breathes, or transpires, in the landscape cooling the air during temperature spikes.
Soil Creates Resilience in the Landscape
Soil is essentially a vast organism that is active under the ground. Because sunlight does not reach it, soil cannot photosynthesize energy so it depends on the plants above ground to do that job for it. Plants use the energy of the sun to capture carbon. They use the carbon to build their bodies and the excess they send down into their roots. The roots exude that excess carbon through their root tips as sugars and those sugars feed the multiplicity of organisms in the soil.
Before the development of the electron microscope, soil was thought to be a collection of mostly organic material and minerals. In the 1930s scientists were able to view those microorganisms in the soil for the first time and they found that a teaspoon of soil could hold billions of those organisms. What they discovered is that in exchange for the sugars that the plants provided through their roots, these microorganisms delivered minerals and nutrients back to the plants.
Understanding the basic biology of the soil makes it easier to see how the practices we employ above ground affect the soil. When we leave the soil undisturbed (no digging, tilling or turning of the soil) it holds moisture better, which reduces runoff and erosion.
The minute the soil is disturbed an opening is created for a weed to assert itself, for the soil to become compacted and for erosion to happen. Uncovered soil loses water and oxygen. Left uncovered long enough soil microbes die back and the soil dies with it, compacting and eroding in wind and rain.
Soil that has plants growing in it keeps the microorganisms in the soil happy and they multiply. A diverse array of plantings will attract different microorganisms, which capture different nutrients to feed the plants. Plants grow stronger, get bigger, more resilient to disturbance and resistant to pests and disease.
The best thing a homeowner can do to increase the function of the soil is to feed it. The soil can be fed by planting a diversity of plant types: ferns, grasses, flowering plants, shrubs and of course trees. These plants in turn supply the garden with leaves and debris that can be used to insulate the soil around the plants, or turned into compost to feed the soil directly. When we fertilize organically with compost we are feeding NOT the plants, but the soil microorganisms so that they in turn will feed the plant. Deep roots make for healthier plants and healthier soil.
By contrast, synthetic fertilizers are meant to feed the plants. When plants get their nutrients from synthetic fertilizers they have no need to grow strong roots to reach that interchange with microorganisms. Their roots remain shallow and dependent on fertilizers, not unlike an IV drip. Plants that are fed with synthetic fertilizers grow shallow roots that end up starving the soil. It is far better to feed the soil with compost and organic material for healthy, robust plants.
Compost tea is essentially water and compost. To make compost tea:
- Fill a 5-gallon bucket with water and let it stand overnight to allow the chlorine to evaporate out of the water.
- Stir in 2 cups of compost and allow to ferment for 24 hours.
- Use the tea to water your flower beds and vegetable gardens
Biochar is a powerful carbon-rich soil amendment and is made by burning wood and other organic matter like yard trimmings, pine cones — any biomass that turns up in the garden. It is burned in a largely oxygen-free process called pyrolysis that turns the biomass into a charcoal-like substance with virtually no emissions.
The surface area of the biochar and its carbon stable structure help store carbon in the soil as it draws it down through the roots of trees and plants. Biochar also can house vast quantities of mycorrhizal networks that feed the soil and the plants that grow in them, helping plants communicate with one another through these networks.
Biochar can be inoculated with compost tea or activated with water and used in the top few inches of soil in the garden. Unlike compost, which should be added annually to the garden, biochar only needs to be added to the landscape once and improves the soil over time.
Soil Sequesters Carbon from the Atmosphere
When considering the health of the soil remember that plants and trees pull down carbon from the atmosphere.
Good soil acts like a magnet for carbon.
As more carbon is pulled into the ground through plants, the soil microbiome becomes more activated, making the plants bigger, stronger and needing more carbon. It is a positive feedback loop that has the potential to draw down legacy carbon. Legacy carbon is the carbon that has built up in the atmosphere and is causing climate change.
Farmers are working to do this by changing agricultural practices, but we can chip in by how we manage our yards.
The deeper our plants and trees can reach into the soil and the more we can build it up with organic material, the more carbon can be held in the soil. You can learn more about the role of soil in the carbon cycle with this great Kiss The Ground video.
Our lawns can work as carbon sinks if we follow a few simple practices.
- Mow at no less than 3 inches and let the clippings stay on the lawn to decompose and feed the soil. Grass clippings alone can supply 25 percent of your lawn’s nutrient needs.
- At the beginning of the season, top dress the lawn with about ¼ to ½ inch of compost. It is best to apply after the lawn has been aerated, but otherwise early in the season. Use compost that has been processed at high temperature so that weeds are not introduced.
- Inoculate the soil under your lawn with AMF (arbuscular mycorrhizal fungi) that will help populate the soil with beneficial microorganisms. There are different methods of application, but it is common to mix it with water and spray directly onto the lawn in the spring and fall.
The soil under our feet is our lifeline to a healthy planet. It is not a big technological project that someone else has to figure out for us. Each of us can participate in healing our landscape and making a bright future possible by simply taking care of the soil.
The final article in the One Land series will appear next week, “Can We Change a Habit? How we care for our lawns and properties”
See also:
ONE LAND: Trees Are the Lifeline of the Landscape
The Alien Invaders in Our Own Backyards: How invasive plants are taking over our native landscape
One Land: The grass isn’t always greener. How our obsession with lawns turned toxic.