What role do soil microbes play in a healthy organic lawn?
Soil microbes, bacteria, fungi and other tiny organisms living in the ground, break down organic matter into nutrients grass roots can absorb. CSU Extension calls this process mineralization, and it’s the mechanism behind how organic fertilization works. CSU Extension’s GardenNotes describes one cup of undisturbed native Colorado soil as holding roughly 200 billion bacteria, 20 million protozoa, 100,000 meters of fungi, 100,000 nematodes and 50,000 arthropods, an entire working ecosystem most people never see.
Luke and I talk about soil biology a lot at Clean Air Lawn Care, because this tiny population is doing an enormous amount of the real work in a healthy lawn, almost always out of sight, right beneath your feet. Clean Air Lawn Care’s organic fertilizer is non-toxic and formulated specifically to feed that biology, which is what sets it apart from a synthetic, quick-release product for lawns in Fort Collins, Windsor and Timnath.
What are soil microbes doing?
Bacteria and fungi break down organic material, dead grass clippings, compost, thatch, organic fertilizer, into simpler compounds a plant can take up through its roots. CSU Extension’s GardenNotes on soil microorganisms describes beneficial bacteria as decomposers that help keep nutrients in the root zone, improve soil structure, and compete with disease-causing organisms for the same space. Fungi work in a similar way, growing as long strands called hyphae through the soil, breaking down complex carbon compounds, helping build organic matter, and binding soil particles into larger clumps. Nematodes, tiny roundworms living in that same soil, mostly feed on bacteria and fungi and help spread them through the soil. Earthworms round out the picture, digesting microorganisms and organic matter as they move through the ground.
One especially important relationship is between fungi called mycorrhizae and a grass plant’s own roots. CSU Extension’s GardenNotes describes mycorrhizal fungi as enlarging a root’s effective absorbing area by 100 to 1,000 times, acting almost like an extension of the root system in exchange for sugars from the plant, while also producing glomalin, a compound that binds soil particles together and improves the space roots need to grow.
Humus, the stable, fully broken-down part of organic matter, slowly releases nitrogen, phosphorus and sulfur over time as plants need it. Without that microbial population doing the breaking-down work, those nutrients stay locked in forms a plant simply can’t use.
How much nitrogen does soil biology supply?
CSU Extension’s GardenNotes on soil testing puts a number on this: an estimated half a pound of nitrogen per 1,000 square feet is released during the growing season for every 1 percent of organic matter in the soil. A well-managed soil at 4 to 5 percent organic matter can supply enough nitrogen on its own that extra fertilizer isn’t needed. That’s the underlying reason building organic matter and feeding soil biology pays off over time instead of just producing a one-time green-up.
How is this different from a synthetic, quick-release fertilizer?
A synthetic fertilizer delivers nutrients directly to the plant in a form it can absorb right away, which produces fast, visible green-up but does little to feed the soil’s microbial community. An organic fertilizer feeds that microbial community first, and the microbes release nutrients to the plant gradually as they break the material down, a slower, steadier release instead of a quick pulse. That population keeps working on the lawn’s behalf well after a single application, continuing to break down thatch and cycle nutrients.
Why does fall matter for soil biology specifically?
Fall is a valuable window for microbial activity, because soil temperatures are still warm enough to support it while the grass plant itself is shifting energy toward its roots. Feeding the soil biology now means it’s actively breaking down organic matter and cycling nutrients right when the plant needs those resources most for root and crown development heading into winter.
How can homeowners support soil biology beyond fertilization?
- Limit unnecessary synthetic pesticide use, since some products can affect beneficial soil organisms along with the pests they targetEven a well-fed lawn struggles if water and air can’t move through the soil around its roots.
- Leave fine grass clippings on the lawn as a natural food source for soil microbes
- Aerate to give microbes and roots better access to air, since compaction suffocates biological activity
- Add compost or organic matter periodically to keep feeding the biological system
This is the part of lawn care that never shows up in a quick before-and-after photo, but it’s the part Luke and I care about most, because it’s what makes a lawn healthy year after year instead of just green for a season. If you want to understand what’s going on in your soil here in Fort Collins, Windsor or Timnath, we’re always glad to talk through it.
Clean Air Lawn Care Northern Colorado is owned by Dianne, Paul, and Luke DeLongchamps — a family business serving Fort Collins, Windsor, and Timnath with organic lawn treatments and solar-powered electric equipment.
