Composting is better than landfilling because it avoids producing methane, a greenhouse gas roughly 80 times more potent than carbon dioxide over a 20-year period. When organic waste breaks down in a landfill without oxygen, it generates massive amounts of this gas. Composting breaks down the same material with oxygen, producing mainly carbon dioxide and creating a nutrient-rich soil product instead of pollution. The difference matters more than most people realize: over half of everything sitting in U.S. landfills is organic material that could have been composted.
What Happens to Food Waste in a Landfill
A landfill is not designed to break down waste. It’s designed to store it. When organic material like food scraps, yard trimmings, and paper gets buried under layers of trash, oxygen disappears within months. That shift to an oxygen-free environment triggers anaerobic decomposition, where bacteria produce a gas mixture of roughly 50% methane and 50% carbon dioxide, along with small amounts of other volatile compounds.
Methane is the real problem. Over a 100-year window, it traps 27 to 30 times more heat in the atmosphere than the same amount of carbon dioxide. Over 20 years, the comparison is even worse: methane’s warming potential jumps to 81 to 83 times that of CO2. Landfills are one of the largest human-caused sources of methane emissions in the United States, and food is the single most common material sent to them, making up 24.1% of all municipal solid waste.
Beyond gas, decomposing organic material in landfills also produces leachate, a toxic liquid that seeps through the waste pile. Leachate contains dissolved organic matter, heavy metals, ammonia, and synthetic chemical compounds. During the early acidic phase of decomposition, concentrations of these pollutants are especially high. Ammonia is particularly stubborn. Unlike some contaminants that decrease as the landfill matures, ammonia persists as a long-term pollutant, posing ongoing risks to groundwater and surrounding ecosystems even in older landfills.
How Composting Handles the Same Waste
Composting is aerobic decomposition, meaning it happens in the presence of oxygen. Microorganisms break down organic material into a stable, soil-like product while releasing mainly carbon dioxide and water vapor. Because oxygen is available throughout the process, the methane-producing bacteria that dominate landfills never take over. The result is a dramatically lower climate impact from the same pile of banana peels and grass clippings.
The process also generates moderate heat, which helps kill weed seeds and harmful pathogens. Finished compost hosts a thriving community of beneficial microorganisms that can suppress plant diseases and outcompete harmful bacteria. Some of these microbes produce natural antimicrobial peptides that actively fight off invading pathogens, making compost a form of biological pest control when added to soil.
Compost Stores Carbon in the Ground
One of the less obvious advantages of composting is that it locks carbon into the soil rather than releasing it all into the atmosphere. When compost is applied to land, a significant portion of its carbon resists further breakdown. Research measuring carbon retention found that about 60% of the total organic carbon in applied compost remained sequestered in the soil, roughly matching the compost’s content of chemically stable, hard-to-degrade carbon. The easily broken-down fraction decomposed, but the rest stayed put.
Over longer timeframes, this adds up. An eight-year study of compost-amended pasture found that soil organic carbon stocks increased by 0.6 metric tons of carbon per hectare per year in the top 10 centimeters of soil. Even after subtracting the carbon that was simply delivered by the compost itself, the net gain was 0.3 metric tons per hectare annually. That’s carbon pulled from the waste stream and stored underground instead of cycling through a landfill’s gas vents.
Soil Gets Healthier, Not Just Less Polluted
Composting doesn’t just avoid harm. It creates something useful. Finished compost contains nitrogen, phosphorus, and potassium, the three nutrients plants need most. A typical green waste compost carries around 15.5 grams of nitrogen, 2.25 grams of phosphorus, and 7.14 grams of potassium per kilogram. These aren’t concentrated like synthetic fertilizers, but they release slowly over time, feeding plants steadily rather than in a single burst that can wash away into waterways.
The physical structure of soil improves too. Adding compost increases soil organic matter, sometimes dramatically. Studies have measured average increases of around 3 percentage points in soil organic matter after compost application. That extra organic matter acts like a sponge, helping soil hold more water during dry periods and drain better during heavy rain. It also loosens compacted soil, giving roots more room to grow and reducing erosion. For gardens, farms, and landscaping, this translates to healthier plants that need less irrigation and fewer chemical inputs.
The Scale of What’s Being Wasted
The gap between what could be composted and what actually is remains enormous. According to the EPA, organic materials including food, yard trimmings, wood, and paper make up 51.4% of municipal solid waste in U.S. landfills. That’s more than half of everything Americans throw away, sitting in anaerobic pits generating methane and leachate instead of being turned into a resource.
Food waste alone accounts for nearly a quarter of the landfill stream. Unlike paper or wood, food scraps are wet and dense, making them especially productive methane generators once oxygen disappears. They’re also among the easiest materials to compost, whether through municipal curbside programs, backyard bins, or commercial composting facilities. Every ton of food scraps diverted from a landfill to a compost pile avoids methane emissions and produces material that can improve soil for years afterward.
Composting vs. Landfill Gas Capture
Some modern landfills capture methane and burn it to generate electricity, which reduces emissions. But capture systems are imperfect. They can only be installed after enough gas builds up, which means the first year or more of methane production escapes entirely. Even well-managed systems typically capture only a portion of total emissions, with the rest leaking through cracks, seams, and the landfill surface. Composting avoids producing the methane in the first place, which is a fundamentally different approach: prevention rather than partial cleanup.
Landfill gas capture also does nothing about leachate contamination, doesn’t produce a beneficial soil product, and doesn’t return nutrients to agricultural land. It’s a mitigation strategy for a disposal method, not an alternative to creating something valuable from organic waste.