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Composting: Basic Information

photo: pile of compost
Photo courtesy of Campaign Recycle Maui Inc./compost Maui

compost is organic material that can be used as a soil amendment or as a medium to grow plants. Mature compost is a stable material with a content called humus that is dark brown or black and has a soil-like, earthy smell. It is created by: combining organic wastes (e.g., yard trimmings, food wastes, manures) in proper ratios into piles, rows, or vessels; adding bulking agents (e.g., wood chips) as necessary to accelerate the breakdown of organic materials; and allowing the finished material to fully stabilize and mature through a curing process.

Natural composting, or biological decomposition, began with the first plants on earth and has been going on ever since. As vegetation falls to the ground, it slowly decays, providing minerals and nutrients needed for plants, animals, and microorganisms. Mature compost, however, includes the production of high temperatures to destroy pathogens and weed seeds that natural decomposition does not destroy.

Did You Know That compost Can...
  • Suppress plant diseases and pests.
  • Reduce or eliminate the need for chemical fertilizers.
  • Promote higher yields of agricultural crops.
  • Facilitate reforestation, wetlands restoration, and habitat revitalization efforts by amending contaminated, compacted, and marginal soils.
  • Cost-effectively remediate soils contaminated by hazardous waste.
  • Remove solids, oil, grease, and heavy metals from stormwater runoff.
  • Capture and destroy 99.6 percent of industrial volatile organic chemicals (VOCs) in contaminated air.
  • Provide cost savings of at least 50 percent over conventional soil, water, and air pollution remediation technologies, where applicable.

Organic Materials

photo: compost and a shovel

Yard trimmings and food residuals together constitute 23 percent of the U.S. waste stream, as documented by EPA. An estimated 56.9 percent of yard trimmings were recovered for composting or grasscycled in 2000, a dramatic increase from the 12 percent recovery rate in 1990. Accompanying this surge in yard waste recovery is a composting industry that has grown from less than 1,000 facilities in 1988 to nearly 3,800 in 2000. Once dominated by public sector operations, the composting industry is increasingly entrepreneurial and private-sector driven, led by firms that add value to compost products through processing and marketing. Compost prices have been as high as $26 per ton for landscape mulch to more than $100 per ton for high-grade compost, which is bagged and sold at the retail level.

While yard trimmings recovery typically involves leaf compost and mulch, yard trimmings can also be combined with other organic waste, such as food residuals, animal manure, and biosolids to produce a variety of products with slightly different chemical and physical characteristics. In contrast to yard trimmings recovery, only 2.6 percent of food waste was composted in 2000. The cost-prohibitive nature of residential food waste separation and collection is the primary deterant to expanding food waste recovery efforts. Yet in many communities, edible food residuals are donated to the needy, while inedible food residuals are blended into compost or reprocessed into animal feed. In some areas, composting operations are working with high-volume commercial and institutional food producers to recover their food byproducts, saving these firms significant disposal costs. For more information on organic materials, visit our Organic Materials Web site.

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What to compost - The IN List

  • Animal manure
  • Cardboard rolls
  • Clean paper
  • Coffee grounds and filters
  • Cotton rags
  • Dryer and vacuum cleaner lint
  • Eggshells
  • Fireplace ashes
  • Fruits and vegetables
  • Grass clippings
  • Hair and fur
  • Hay and straw
  • Houseplants
  • Leaves
  • Nut shells
  • Sawdust
  • Shredded newspaper
  • Tea bags
  • Wood chips
  • Wool rags
  • Yard trimmings

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What not to compost - The OUT List

Leave Out...

Reason Why...

Black walnut tree leaves or twigs Releases substances that might be harmful to plants
Coal or charcoal ash Might contain substances harmful to plants
Dairy products (e.g., butter, egg yolks, milk, sour cream, yogurt) Create odor problems and attract pests such as rodents and flies
Diseased or insect-ridden plants Diseases or insects might survive and be transferred back to other plants
Fats, grease, lard, or oils Create odor problems and attract pests such as rodents and flies
Meat or fish bones and scraps Create odor problems and attract pests such as rodents and flies
Pet wastes (e.g., dog or cat feces, soiled cat litter) Might contain parasites, bacteria, germs, pathogens, and viruses harmful to humans
Yard trimmings treated with chemical pesticides Might kill beneficial composting organisms

NOTE: Finished compost can be applied to lawns and gardens to help condition the soil and replenish nutrients. Compost, however, should not be used as potting soil for houseplants because of the presence of weed and grass seeds.

U.S. Environmental Protection Agency
1200 Pennsylvania Avenue, NW
Washington, DC 20460
www.epa.gov