Products, Vendors, CAD Files, Spec Sheets and More...
Sign up for LAWeekly newsletter
Composting can be traced at least as far back as Marcus Cato, a farmer and statesman from Rome, who lived over 2,200 years ago. He reported the virtues of compost for enhancing agricultural productivity, stating that all food and animal wastes should be composted and returned to the soil. In the United States, George Washington was an avid composter who designed a building specifically for that purpose on his farm in Mount Vernon, New York. By the 19th century, composting was commonly practiced to restore organic matter to soils.
Today, Americans generate more than 240 million tons of trash (solid waste) each year, or 4.5 pounds per person on a daily basis. Of this amount, 72 million tons (31%) is recycled, a number that has been rising steadily as communities work to conserve landfill space. Municipalities and universities are taking part as well, with many erecting composting facilities on site taking advantage of their own trash and debris. In addition, the number of licensed composting facilities operating in the United States today has tripled since 1990, to over 3,000. Commercial composting processes 17 million tons of yard and food wastes and is responsible for a quarter of the recycling that occurs annually in the United States, as reported in 2005 by the United States Environmental Protection Agency.
The California Integrated Waste Management Act (resulting from Assembly Bill 939, Sher.) mandated a 25% diversion of organic waste from landfills by cities and counties by 1995 through source reduction, recycling, and composting activities and a 50% diversion by 2000 (based on 1990 levels). Due largely to this legislation, diversion rates have increased dramatically from 11 to 50% between 1989 and 2006.
In California, when looking at the acres of turf trimmed both commercially and by homeowners, grass trimmings account for the largest single component of municipal waste. These clippings comprise approximately half of the yard trimmings deposited in state landfills. In fact, an average California lawn produces 300 to 400 pounds of grass clippings per 1,000 square feet annually, which equates to as much as 8 tons per acre each year. Leaves and grass contribute up to a million tons of material each year, or 8% of the California waste stream. When commercial prunings, branches, stumps, and similar compostables are tallied, the total increases to over 13% or 1.7 million tons of material every year. Composting also provides a means to recycle millions of tons of crop residues, stable bedding materials, manures, food wastes and other organic materials in a sustainable and environmentally beneficial manner.
Besides conserving landfill space, composting benefits the environment.
Composts used as soil amendments add valuable organic matter to the planting bed and can significantly improve plant growth and development, particularly in depleted or damaged soils. Compost use can also improve water quality. Healthy plant coverage is considered to be the single most important ?EUR??,,????'??Best Management Practice?EUR??,,????'??? for controlling stormwater runoff and reducing soil erosion.
Composts improve soils and promote plant health, particularly in poor quality, problem or damaged soils commonly encountered in landscapes. Within and on the soil, compost is used to:
Compost is generated when organic matter is consumed and decomposed by microorganisms under favorable environmental conditions. Key management factors for the compost process include maintaining a good nutrient balance, correct moisture content and temperatures, and adequate aeration.
The most important nutrient balance concern when generating compost is the ratio of carbon to nitrogen (C:N) in the decomposing mixture. Bacteria, actinomycetes and fungi use available carbon for energy they require to grow and reproduce and nitrogen to build protein and genetic material.
The moisture content of compost should ideally be about 60% after mixing. Microbes need water to live and grow, but too much will block the supply of fresh air which contains the oxygen that they also need. A general rule of thumb is that a handful of compost should feel moist and hold together without dripping, but not be so dry that it won?EUR??,,????'???t mold. While composting actually generates moisture, a significant amount is usually removed by air flowing through the compost pile. Therefore, moisture often must be added during composting to support an active process.
The temperature increases that occur during the composting process result from the breakdown of organic material by bacteria, actinomycetes, fungi, and protozoa. Compost piles can reach 150?????F in less than 2 days. Applying heat to compost from an external source is not necessary since heat is generated from within the compost pile.
As microorganisms decompose (oxidize) the available organic matter, heat is generated and released into the compost. Much of the generated heat is retained in the pile because compost is an excellent insulator and can result in rapid temperature increases. As temperatures increase, the efficiencies of the microbes increase exponentially until around 150?????F. At that point, the composting rate drops rapidly, becoming negligible above 160?????F, since such high temperatures kill the microbes in the pile. The majority of compost formation should occur when temperatures are in the thermophilic (100-150?????F) range. The Environmental Protection Agency has found that decomposing organic matter exposed to 131?????F for 3 days is enough to eliminate parasites, fecal matter, and plant pathogens. Turning the pile regularly to allow cooler surface zones to mix with hot center areas is recommended to maintain 131????? F.
A fresh supply of air is vital for composting. Proper aeration is needed to control the environment required for biological processes to thrive with optimum efficiency.
Bulking agents are typically wood, straw, or similar materials added to the compost mixture to increase porosity and improve aeration. Because smaller particles provide greater surface area to microbes than larger ones, they decompose more rapidly than bulking agents.
When compost preparation is correct, the active phase will start immediately and thermophilic conditions will be reached as microbes consume readily available carbon and nitrogen-containing compounds. After several days or weeks (based on the quantity and sizes of the feedstock), the temperature will drop and the mesophiles will take over, consuming lignin and other hard to decompose organic materials.
Materials are typically repiled for this curing phase. Compost is considered finished, stable, and mature when:
Feedstock is materials used to manufacture the compost product. Compost can be derived from a number of feedstock materials including woody (trees, shrubs) and herbaceous (turfgrass and small flowering plants) greenwaste, crop residues, biosolids (sewage sludge), wood by-products, animal manures, biodegradable packing and building materials and food scraps.
Feedstock materials, even within a particular type, can vary significantly depending on the conditions under which they were collected and processed. The composting process dramatically changes the properties of these feedstock materials, resulting in greater uniformity and consistency. Among the more frequently encountered feedstock materials are:
Francisco Uviña, University of New Mexico
Hardscape Oasis in Litchfield Park
Ash Nochian, Ph.D. Landscape Architect
November 12th, 2025
Sign up to receive Landscape Architect and Specifier News Magazine, LA Weekly and More...
Invalid Verification Code
Please enter the Verification Code below
You are now subcribed to LASN. You can also search and download CAD files and spec sheets from LADetails.