Composting is the process of breaking down organic waste, like food scraps and yard trimmings, into a nutrient-rich soil amendment through controlled biological decomposition. Microorganisms (bacteria, fungi, and other tiny life forms) consume organic material and, given the right balance of air, moisture, and nutrients, transform it into a dark, crumbly substance that enriches soil and diverts waste from landfills. In the United States, about 25 million tons of municipal solid waste were composted in 2018, yet only 4.1 percent of food waste was composted that year, leaving enormous room for growth.
How Composting Works
At its core, composting is a feeding frenzy. Billions of bacteria and fungi colonize a pile of organic material and begin eating through it. As they digest, they generate heat, sometimes pushing internal temperatures above 55°C (131°F). That heat is a feature, not a bug: it kills weed seeds and harmful bacteria, essentially sanitizing the finished product. EPA regulations for composting certain materials require maintaining at least 55°C for three consecutive days in enclosed systems, or 15 days with regular turning in open piles, to ensure pathogens are destroyed.
The whole process hinges on oxygen. When microbes have access to air (aerobic conditions), they break down material efficiently with relatively little odor. When oxygen is cut off, a different set of bacteria takes over, producing methane and foul-smelling compounds. This is exactly what happens when food waste sits buried in a landfill, sealed under layers of trash. Composting keeps the process aerobic by design.
The Carbon-to-Nitrogen Balance
Every compost pile needs two broad categories of ingredients, often called “browns” and “greens.” Browns are carbon-rich materials: dry leaves, plant stalks, twigs, shredded cardboard (without wax or tape), shredded non-glossy paper, and untreated wood chips. Greens are nitrogen-rich: fruit and vegetable scraps, grass clippings, coffee grounds with their paper filters, paper tea bags, and crushed eggshells.
The ideal ratio is roughly 30 parts carbon to 1 part nitrogen by weight. When nitrogen is too high relative to carbon, excess nitrogen escapes as ammonia gas, which is what creates that sharp, unpleasant smell from poorly managed piles. When carbon is too high, microbes don’t have enough nitrogen to fuel their growth, so the pile stays cool and breaks down very slowly. In practice, layering a few handfuls of greens with a thicker layer of browns, then mixing periodically, keeps most backyard piles in a productive range.
Why It Matters for the Climate
Organic waste buried in landfills decomposes anaerobically, generating large amounts of methane, a greenhouse gas far more potent than carbon dioxide in the short term. In 2014, U.S. landfills produced the equivalent of 181.8 million metric tons of CO₂ from methane alone. Composting operations that same year produced just 2.1 million metric tons. Per ton of waste processed, composting generates less than 10 percent of the greenhouse gases that landfilling does. That gap makes waste diversion to composting one of the more straightforward ways to reduce emissions from the waste sector.
Home Composting Methods
The simplest approach is a backyard bin or open pile. You add browns and greens in layers, keep the pile about as moist as a wrung-out sponge, and turn it every week or two to introduce oxygen. A well-managed pile can produce finished compost in two to six months depending on what goes in, how often you turn it, and your local climate. Hotter weather speeds things up considerably.
Worm Composting
Vermicomposting uses specialized composting worms, most commonly a species called red wigglers, to process food scraps indoors or in a sheltered outdoor bin. These worms are popular because they reproduce quickly, adapt well to bin conditions, and stay small. They need moisture levels around 80 to 90 percent (think the consistency of damp bedding), temperatures between 13°C and 25°C (roughly 55°F to 77°F), and a slightly alkaline environment. The worms eat through food scraps and shredded paper, and their castings (waste) become an especially nutrient-dense form of compost. Vermicomposting works well for apartment dwellers or anyone without yard space.
Bokashi Fermentation
Bokashi is an anaerobic method that uses a sealed bin and a grain inoculant loaded with lactic acid bacteria, yeast, and sometimes other beneficial microorganisms. You layer food scraps with the inoculated grain in an airtight container. The bacteria lower the pH rapidly, fermenting the waste rather than decomposing it in the traditional sense. Within a few weeks, the material shrinks significantly in volume and moisture. It isn’t finished compost at that stage. You either bury the fermented material in soil, where worms and soil organisms finish the job, or add it to a traditional compost pile. Bokashi handles items that standard composting struggles with, like cooked food and small amounts of dairy, because the sealed, acidic environment suppresses the bacteria that cause rot and attract pests.
Industrial Composting vs. Home Composting
Industrial composting facilities control temperature, moisture, and oxygen levels precisely, processing large volumes of waste at consistently high temperatures. This matters for more than just speed. Many products labeled “compostable,” particularly bioplastic items like plant-based utensils and food packaging, require industrial conditions to break down. These materials carry a seedling logo certifying they meet industrial composting standards, but research from University College London found that consumers often don’t understand the distinction between industrially compostable and home compostable. A bioplastic fork tossed into a backyard bin will likely sit there unchanged for years because home piles rarely sustain the temperatures and microbial activity that industrial facilities maintain.
If your municipality offers curbside organics collection or operates a drop-off composting program, those materials typically go to an industrial facility where certified compostable packaging can actually break down. Without that infrastructure, it’s best to treat “compostable” plastics as regular trash rather than contaminating a home pile with material that won’t decompose.
What the Finished Product Does
Finished compost is dark, crumbly, and smells like forest floor. Mixed into garden soil, it improves structure in both directions: it helps sandy soil retain water and nutrients, and it loosens dense clay soil so roots can penetrate more easily. It introduces a thriving community of beneficial microorganisms to the soil, supports earthworm populations, and slowly releases nitrogen, phosphorus, and potassium as plants need them. Unlike synthetic fertilizers, compost feeds the soil ecosystem rather than just the plant, building long-term fertility instead of providing a short-term nutrient spike.
For home gardeners, a few inches of compost worked into garden beds at the start of each growing season can noticeably improve plant health and reduce the need for purchased amendments. For municipalities, large-scale composting turns a disposal cost into a usable product while cutting landfill methane emissions significantly.