Composting

Composting is a way for gardeners and farmers to enrich and otherwise improve the soil while reducing the flow of household waste to landfills. Essentially the slow natural decay of dead plants and animals, composting is a natural form of recycling in which living organisms decompose organic matter.

Background

The decay of dead plants and animals starts when microorganisms in the soil feed on dead organic matter, breaking it down into smaller compounds usable by plants. Collectively, the breakdown product is called humus, a dark brown, spongy, crumbly substance. Adding humus to soil increases its fertility. Compost may be defined in various ways. The Oxford English Dictionary defines it (as a noun) as a mixture of ingredients for fertilizing or enriching land, a prepared manure or mold; Webster’s New World Dictionary defines it (as a verb) as the making of compost and the treatment of soil with it. “Compost” and “composting” both derive from the Old French composter, “to manure” or “to dung.”

History

The origins of human composting activities are buried in prehistory. Early farmers undoubtedly discovered the benefits of compost, probably from animal manure deposited on or mixed with soil. In North America, American Indians and then Europeans used compost in their gardens. Public accounts of the use of stable manure in composting date back to the eighteenth century. Many New England farmers also found it economical to use fish in their compost heaps.

While living in India from 1905 to 1934, British agronomist Sir Albert Howard developed modern home composting methods. Howard found that the best compost pile consists of three parts plant matter to one part manure. He devised the Indore method of composting, alternating layers of plant debris, manure, and soil to create a pile. Later, during the composting process, he turned the pile or mixed in earthworms.

How Composting Works

Composting is a natural form of recycling that takes from six months to two years to complete. Bacteria are the most efficient decomposers of organic matter. Fungi and protozoans later join the process, followed by centipedes and millipedes, beetles, and earthworms. By manipulating the composition and environment of a compost pile, gardeners and farmers can reduce composting time to three to four months. Important factors to consider are the makeup of the pile, the surface area, the volume, the moisture, the aeration, and the temperature of the compost pile.

Yard waste such as fallen leaves, grass clippings, some weeds, and the remains of garden plants make excellent compost. Other good additions to a home compost pile include sawdust, wood ash, and kitchen scraps, including vegetable peelings, egg shells, and coffee grounds. Microorganisms digest organic matter faster when they have more surface area to work on. Gardeners can speed the composting process by chopping kitchen or garden waste with a shovel or running it through a shredding machine or lawn mower.

The volume of the compost pile is important because a large compost pile insulates itself, holding in the heat of microbial activity. A properly made heap will reach temperatures of about 60 degree Celsius in four or five days. Then the pile will settle, a sign that is working properly. Piles 0.76 cubic meters or smaller cannot hold enough heat, while piles 3.5 cubic meters or larger do not allow enough air to reach the microbes in the center of the pile. These portions are important only if the goal is fast composting. Slower composting requires no exact proportions.

Moisture and air are essential for life. Microbes function best when the compost heap has many air passages and is about as moist as a wrung-out sponge. Microorganisms living in the compost pile use the carbon and nitrogen contained in dead matter for food and energy. While breaking down the carbon and nitrogen molecules in dead plants and animals, they also release nutrients that higher organisms such as plants can use.

The ratio of carbon to nitrogen found in kitchen and garden waste varies from 15:1 in food waste to 700:1 in wood. A carbon-to-nitrogen ratio of 30:1 is optimum for microbial decomposers. This balance can be achieved by mixing two parts of grass clippings (carbon-to-nitrogen ratio, 19:1) and one part of fallen leaves (carbon-to-nitrogen ratio, 60:1). This combination is the backbone of most home composting systems.

Modern Uses and Practice

Composting remains an important practice. Yard and kitchen wastes use valuable space in our landfills. These materials compose about 20 to 30 percent of all household waste in the United States, but according to a 2022 EPA report, only 4.1 percent of wasted food makes it to a composting pile. Composting household waste reduces the volume of municipal solid waste and provides a nutrient-rich soil additive. Furthermore, organic matter that becomes buried in landfills is a major source of methane emissions, a greenhouse gas. Compost or organic matter added to soil improves soil structure, texture, aeration, and water retention. It improves plant growth by loosening heavy clay soils, allowing better root penetration. It improves the water-holding and nutrient-holding capacity of sandy soils and increases the essential nutrients of all soils. Mixing compost with soil also contributes to erosion control and proper soil pH balance.

Some cities collect and compost leaves and other garden waste and then make it available to city residents for little or no charge. Some cities also compost sewage sludge or human waste, which is high in nitrogen and makes a rich fertilizer. Properly composted sewage sludge that reaches an internal temperature of 60 degrees Celsius contains no dangerous disease-causing organisms. However, it may contain high levels of toxic heavy metals, including zinc, copper, nickel, and cadmium.

The basic principles of composting used by home gardeners are also used by municipalities composting sewage sludge and garbage, by farmers composting animal and plant waste, and by some industries composting organic waste. Food and fiber industries, for example, compost waste products from canning, meat processing, dairy, and paper processing.

Technology in the 2020s has made composting easier and more efficient than in the past. Small-scale systems have been designed for environments with little space. Despite their size, these systems have a significant processing capacity and are suitable for businesses as well as households. They also control odor and reduce greenhouse gas emissions.

Vermicomposting

One relatively recent form of composting is vermicomposting, or using worms to convert organic matter to compost. Earthworms have long been celebrated for their ability to break down organic matter into humus. In 1972, Michigan biology teacher Mary Appelhof developed the idea of home vermicomposting as a way to continue composting in the winter. Over the course of one winter, one pound of Eisenia fetida, or red wriggler worms, converted sixty-five pounds of garbage into worm compost in a bin in her basement. She published her method in her two brochures, in 1973 and 1979, and then in the 1982 book Worms Eat My Garbage. Appelhof also organized a workshop in Kalamazoo, Michigan, in 1979, with funding from the National Science Foundation, that brought together international scientists, entrepreneurs, and commercial earthworm breeders to discuss the possibilities of vermicomposting.

Around the same time, in England, soil ecologist Clive Edwards was researching the development of large-scale vermicomposting operations, known as continuous-flow systems. Large-scale vermicomposting began in England, Canada, and the Netherlands in the 1980s. In the United States, the first large-scale continuous-flow vermicomposting processor was built by the Oregon Soil Corporation in Portland, Oregon, in 1991.

To be suitable for vermicomposting, earthworms must be detritivores, meaning they feed on organic waste, and they must be epigeic, or surface dwelling. Only a handful of earthworm species are known to fit the criteria, and of them, only five have been extensively used: red wrigglers; Eisenia andrei, a close relative; Eisenia hortensis, the European nightcrawler; Perionyx excavatus, also called blues or Indian blues; and Eudrilus eugeniae, also called African nightcrawlers.

Bibliography

Appelhof, Mary. Worms Eat My Garbage. 35th anniversary ed., Storey Publishing, 2017.

Bem, Robyn. Everyone’s Guide to Home Composting. Van Nostrand Reinhold, 1978.

Campbell, Stu. Let It Rot! The Gardener’s Guide to Composting. 3rd ed., Storey Publishing, 1998.

"Composting at Home." United States Environmental Protection Agency, 27 Sept. 2024, www.epa.gov/recycle/composting-home. Accessed 23 Dec. 2024.

"Composting." Cornell Waste Management Institute, Cornell U, cwmi.css.cornell.edu/composting.htm. Accessed 23 Dec. 2024.

Ebeling, Eric, editor. Composting Basics: All the Skills and Tools You Need to Get Started. With Carl Hursh and Patti Olenick, 2nd ed., Stackpole Books, 2017.

Edwards, Clive A., et al., editors. Vermiculture Technology: Earthworms, Organic Wastes, and Environmental Management. CRC Press, 2011.

Markham, Brett L. The Mini Farming Guide to Composting: Self-Sufficiency from Your Kitchen to Your Backyard. Skyhorse Publishing, 2013.

Martin, Deborah L., and Grace Gershuny, editors. The Rodale Book of Composting: Easy Methods for Every Gardener. Rev. ed., Rodale Press, 1992.

Parrish, Rogue. "The History of Vermicomposting." Garden Guides, Leaf Group, 21 Sept. 2017, www.gardenguides.com/121248-history-vermicomposting.html. Accessed 23 Dec. 2024.

“Reducing the Impact of Wasted Food by Feeding the Soil and Composting.” Environmental Protection Agency, 15 Nov. 2022, www.epa.gov/sustainable-management-food/reducing-impact-wasted-food-feeding-soil-and-composting. Accessed 23 Dec. 2024.

Simons, Margaret. Resurrection in a Bucket: The Rich and Fertile Story of Compost. Allen & Unwin, 2004.

"USCC Position: Keep Organics out of Landfills!" US Composting Council, Aug. 2012, nrcne.org/wp-content/uploads/2019/12/Keeping-Organics-Out-of-Landfills-POSITION-STATEMENT-Final-7-18-12.pdf. Accessed 23 Dec. 2024.

Woods, Scott. "Innovations in Composting Technology: Reducing Footprint and Increasing Efficiency." Waste Advantage, 31 Oct. 2023, wasteadvantagemag.com/innovations-in-composting-technology-reducing-footprint-and-increasing-efficiency/. Accessed 23 Dec. 2024.