Composting turns food scraps and yard waste into dark, crumbly soil. Microbes do the work. Bacteria and fungi break down organic matter, generating heat in the process. A well-managed pile reaches 55 to 65 degrees Celsius, hot enough to kill pathogens and weed seeds. The result is humus, a nutrient-rich material that improves soil structure.

The process needs four things: carbon-rich browns like leaves and cardboard, nitrogen-rich greens like grass and food scraps, water, and air. The ratio matters. Too much of one ingredient slows decomposition. Turning the pile adds oxygen and speeds things up. A balanced pile can finish in a few weeks. A neglected one takes months.

Composting keeps organic waste out of landfills. In landfills, food scraps decompose without oxygen and release methane, a potent greenhouse gas. Composting avoids that. Cities from San Francisco to Milan run collection programs. Home composting works too. A small bin in a backyard can handle most kitchen scraps.

Key ingredients

• Browns: leaves, cardboard, straw
• Greens: food scraps, grass clippings
• Water
• Air
• Time