How Composting Helps the Environment

Composting turns plant parts into nutrients for the next generation of plants.


In 2009, the City of San Francisco introduced the "Mandatory Recycling and Composting Ordinance," which required all San Franciscans to separate their trash into recyclables, compostables and landfill trash. Before the ordinance was enacted, the city determined that 36 percent of the trash going to landfills was compostable food waste. Since the program began, one million tons of plant waste has been turned into compost. Following San Francisco's lead, Boulder, Seattle and Portland have begun their own curbside recycling programs. Diverting plant waste into compost has a number of benefits for the environment.

Helps Landfills

Composting helps keep vegetable matter out of landfills. Not only does composting keep landfills from filling up prematurely, it minimizes the pollution they create. Plant matter doesn't decay cleanly when placed in landfills: The layers of trash burying the plant matter create an anaerobic environment. This airless environment causes the plant matter, as it decays, to produce methane gas as it decays. This potent greenhouse gas is 21 times more potent than carbon dioxide. Consequently, composting helps minimize landfills' contribution to climate change.

Feeds the Soil

Jared Eliot, in his classic 1748 book "Essays Upon Field Husbandry," introduced an often-cited metaphor. The soil, he said, is like a bank. A person who grows food in the soil without returning plant wastes and manure to it is like a person who repeated withdraws cash from a bank account without ever making a deposit. Composting food waste, then returning that compost to fields and gardens, allows us to return nutrients to the soil bank that feeds us.

Improves the Soil

Compost improves the soil in many ways. It helps loosen the compaction of heavy soils. It helps sandy soils trap and hold water. When mixed with soil, compost functions like a sponge, holding water where the roots need it most, reducing the amount of irrigation a crop needs. Composting adds nutrients and fosters the growth of beneficial microorganisms, insects and earthworms. It also helps to minimize wind and water erosion both by holding onto moisture in the soil and by encouraging healthy root growth. Overall, compost makes major contributions to soil health, increasing the chance of plant success.

Minimizes Chemicals

Spreading compost on cropland minimizes the need for chemical fertilizers. Compost not only provides the basic nutrients supplied by chemical fertilizers -- nitrogen, potassium and phosphorus -- it provides a wide array of trace minerals and other nutrients not available in chemical fertilizers. Less use of chemical fertilizers reduces their associated environmental problems, including water pollution. Nitrogen from these fertilizers causes algae blooms in lakes and the ocean, radically altering the coastal ecosystem. Chemical fertilizers also leach into groundwater and contaminate drinking water wells.

Resources (1)

  • How to Grow More Vegetables; John Jeavons

About the Author

Susan Peterson


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  • Hemera Technologies/ Images
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