Composting is one of the most effective things you can do to reduce your environmental footprint. It cuts methane emissions from landfills, builds healthier soil, locks carbon underground, and reduces the need for synthetic fertilizers. The benefits are well documented, and the gap between what we could be composting and what we actually do is enormous: in 2019, only 5% of the 66.2 million tons of wasted food generated by U.S. homes, restaurants, and retailers was composted.
Landfill Methane Is the Big One
When food scraps and yard waste end up in a landfill, they decompose without oxygen and produce methane, a greenhouse gas roughly 80 times more potent than carbon dioxide over a 20-year window. Municipal solid waste landfills are the third-largest source of human-caused methane emissions in the United States, and food waste drives the bulk of the problem. Food makes up about 24% of what goes into landfills, yet it’s responsible for an estimated 58% of the methane that escapes from those sites into the atmosphere.
Composting sidesteps this entirely. In a compost pile, organic material breaks down with oxygen present, which produces carbon dioxide instead of methane. Carbon dioxide is still a greenhouse gas, but it’s far less powerful, and the net climate impact is dramatically lower. Globally, food loss and waste account for 8 to 10% of all human-caused greenhouse gas emissions, according to the IPCC. Diverting even a fraction of that waste into composting systems would meaningfully shrink that number.
Healthier Soil That Holds More Water
Compost transforms soil structure. It adds organic matter, which acts like a sponge, improving the soil’s ability to absorb and retain water. Soil scientists at Michigan State University report that for every 1% increase in organic matter content, soil can hold 16,500 gallons of plant-available water per acre at a depth of one foot. That’s a significant buffer during dry spells, and it means less irrigation, less runoff, and more resilient crops and gardens.
The benefits go deeper than water retention. Compost loosens compacted clay soils, gives sandy soils something to hold onto, and creates the pore structure that plant roots need to grow. Over time, compost-amended soil becomes a self-improving system: better structure supports more root growth, which supports more microbial life, which further improves the soil.
A Boost for Soil Microbes
Healthy soil teems with bacteria, fungi, and other microorganisms that cycle nutrients, fight plant diseases, and maintain soil structure. Compost feeds this underground ecosystem. Research on temperate cropland in China found that adding compost significantly increased the density of soil bacteria, fungi, and actinomycetes compared to untreated soil. It also boosted microbial diversity, as measured by the Shannon index, a standard metric for biological variety.
Synthetic nitrogen fertilizer, by contrast, pushed microbial diversity in the opposite direction. Soils treated only with synthetic nitrogen had lower diversity scores and fewer beneficial organisms. This matters because diverse microbial communities are more resilient and better at suppressing plant pathogens. Compost doesn’t just add nutrients to soil. It builds the living system that makes nutrients available to plants over the long term.
Erosion and Runoff Control
Compost spread as a surface blanket is remarkably effective at preventing erosion. A study on roadside slopes found that compost blankets 1 to 2 inches thick reduced suspended sediment loss by 90 to 99% compared to unprotected ground. A Massachusetts Department of Transportation project reported similar results, with erosion reductions of 95 to 97%. In some treated plots, researchers collected no runoff at all, even under heavy rainfall, because the compost layer absorbed water before it could flow downhill.
This absorption capacity also prevents nutrient pollution. When rain washes bare soil into streams, it carries nitrogen and phosphorus that fuel algal blooms and degrade water quality. Compost blankets trap those nutrients in place, keeping them in the soil where plants can use them rather than letting them reach waterways.
Carbon Sequestration in Soil
Composting doesn’t just prevent greenhouse gas emissions. It actively pulls carbon out of the atmosphere and stores it in the ground. When compost is added to soil, a substantial portion of its carbon resists further breakdown and remains locked in the soil for years or decades. Research measuring carbon retention over 150 days found that compost-amended soil stored 4.2 to 6.8 metric tons of carbon per hectare, depending on application rate. Roughly 62% of the carbon in the compost stayed in the soil rather than returning to the atmosphere.
Scaled across farmland, gardens, and public landscapes, this adds up. Every ton of compost applied is both a waste diversion strategy and a carbon storage strategy, doing double duty for the climate.
Less Need for Synthetic Fertilizer
Compost delivers nitrogen, phosphorus, potassium, and micronutrients in a slow-release form that plants absorb over months. This reduces dependence on synthetic fertilizers, which carry their own environmental costs. Manufacturing synthetic nitrogen fertilizer requires extremely high temperatures and pressures, powered mostly by burning fossil fuels. Between production and field application, fertilizers contribute an estimated 2% of global greenhouse gas emissions.
Compost can’t always replace synthetic fertilizer entirely, especially in large-scale agriculture where precise nutrient ratios matter. But even partial substitution cuts emissions from manufacturing, reduces the risk of nutrient runoff (because compost releases nutrients slowly rather than in a single burst), and builds long-term soil fertility that synthetic products don’t provide.
Cleaning Up Contaminated Soil
One of the lesser-known environmental benefits of compost is bioremediation: using compost to break down pollutants in contaminated soil. The microbial communities in compost can degrade or transform a wide range of contaminants, including hydrocarbons, solvents, pesticides, wood-preserving chemicals, and petroleum products. In one documented case, soil contaminated with 3,000 parts per million of a common herbicide was remediated to undetectable levels in just 50 days using compost.
This approach is cheaper and less disruptive than hauling contaminated soil to a treatment facility, and it leaves behind healthier soil rather than a barren site.
Potential Downsides to Watch For
Composting isn’t without risks, though they’re manageable. Compost made from sewage-based materials can contain heavy metals like lead, arsenic, and cadmium. Regulatory limits exist for these contaminants, but quality varies across products. If you’re buying compost, look for products tested under the U.S. Composting Council’s Seal of Testing Assurance program, or choose compost made from food scraps and yard waste rather than biosolids.
Poorly managed compost piles can also produce odors and, in anaerobic pockets, generate some methane. Turning your pile regularly and maintaining the right balance of carbon-rich “browns” (leaves, cardboard) and nitrogen-rich “greens” (food scraps, grass clippings) prevents this. At the industrial scale, well-run composting facilities monitor oxygen levels and temperature to keep decomposition aerobic and efficient.
There’s also a scale problem. With only 5% of wasted food being composted in the U.S., the infrastructure for collection and processing lags far behind the opportunity. Expanding access to curbside composting programs and commercial facilities is one of the most impactful steps municipalities can take to capture the environmental benefits that composting offers.