Building Organic Matter
Soil Health
Organic matter is the fraction of your soil made up of living organisms, fresh plant and animal residues, and the stable, decomposed material often called humus. For home gardeners across the United States, steadily building organic matter is one of the most reliable ways to improve almost any garden soil over time.
What it is
Organic matter typically makes up only a small percentage of a garden soil by weight, yet it influences how the soil holds water, stores nutrients, and resists compaction. It gives topsoil its dark color and crumbly, well-aggregated structure, and it feeds the earthworms, fungi, and bacteria that keep soil biologically active. As residues break down, some carbon is released while a portion becomes stable humus that lingers in the soil for years. Building it is a gradual process because material is continually decomposing, so gains come from adding organic inputs consistently rather than all at once.
What to do
Add organic materials regularly, such as finished compost, shredded leaves, grass clippings, and other plant residues worked into or laid on top of the soil. Grow cover crops during the off-season and turn them under or cut them down before they set seed to return their growth to the soil. Keep the ground covered with mulch or living plants and minimize deep, frequent tilling, which speeds the breakdown of the organic matter you are trying to accumulate. Leaving healthy plant roots in place and rotating crops also helps sustain the soil life that drives the process.
Tips
A standard soil test can report your organic matter percentage, giving you a baseline to track improvement season over season. Contact your local Cooperative Extension office to interpret those results and to get recommendations tailored to your soil, climate, and the materials available in your region. Expect slow, steady change, and keep records of what you add so you can see progress across several years.
General guidance for US gardens. For specific nutrient, pH, and amendment rates, have your soil tested through your local Cooperative Extension office. Page updated Aug 4, 2026.