Composting: Nature's Most Interesting Process

What It Covers

Josh Clark and Chuck Bryant break down home composting on Stuff You Should Know, covering why diverting food waste from landfills matters, how to set up a bin, what materials to add or avoid, and the three-phase biological process that transforms kitchen scraps into nutrient-rich humus fertilizer.

Key Questions Answered

• •Landfill methane problem: Food waste comprises 40% of all US landfill material. Landfills use anaerobic decomposition, which produces methane — a greenhouse gas 70% more potent than carbon dioxide. Composting the same material aerobically produces carbon dioxide instead, while simultaneously extending landfill lifespan and generating usable fertilizer from what would otherwise be wasted space.
• •Carbon-to-nitrogen ratio: Maintain a roughly 30-to-1 carbon-to-nitrogen ratio for an efficient pile. A practical rule: green or recently living materials (banana peels, grass clippings, coffee grounds) are nitrogen-rich; brown, dry materials (newspaper, corn cobs, dried leaves) are carbon-rich. Layer these proportions when adding material rather than measuring precisely with instruments.
• •Pile location and structure: Place the bin under a deciduous tree — bare winter branches allow sunlight to warm the pile in cold months, while summer leaf cover prevents drying. Single-bin systems work for beginners (new material on top, finished humus at bottom); three-bin systems allow staged decomposition but require active daily management to rotate material between chambers.
• •Three-phase temperature cycle: A compost pile progresses through mesophilic (up to 40°C), thermophilic (50–65°C), and curing phases. The thermophilic stage, reaching 100–150°F, kills pathogens, parasites, and disease organisms naturally. Exceeding 65°C kills beneficial microbes and stalls the process, so regular turning and moisture management keep temperatures in the productive range throughout decomposition.
• •What not to compost: Avoid meat, dairy, diseased plants, pesticide-treated vegetation, invasive weeds (specifically buttercup, morning glory, and quack grass whose seeds survive composting), pet waste, and charcoal ash. Wood ash raises pile alkalinity enough to halt microbial activity. Grass clippings in excess create too much nitrogen, producing ammonia gas and odor rather than useful decomposition byproducts.