Composting, nature’s own way of recycling, is the controlled decomposition of organic material such as leaves, twigs, grass clippings, and vegetable discards. Composting produces useful soil amendment products. Whether done on-site or in a large-scale facility, composting helps to keep the high volume of organic material out of landfills. Onsite composting eliminates the hauling materials and is generally exempted from solid waste regulations. Large-scale facilities produce a more consistent product under regulatory oversight. For additional information on regulations, contact your local enforcement agency.
The following sections provide basic composting information to get you started. The principles of composting are the same if you have one cubic yard or hundreds. Small scale landscapers process organic materials usually without regulatory oversight. Before beginning any composting operation, check with the proper regulatory agencies. See information below in the Off Site section under Regulations. Since composting involves the decay of organic materials, consider the impact an operation could have on others. Neighbors complain when poorly run operations produce odor, dust, or excessive noise.
Backyard composting happens in an open pile or a homemade/manufactured composting bin. Businesses, schools, and other facilities compost, too. Some professional landscapers offer composting as a service for their clients. This saves trips to the dump and produces compost for the client.
Contact your city or county government for information about free composting workshops and discounted composting bins, obtain ready-to-use bins through retail or mail-order establishments, or punch side and bottom holes in an old garbage can to start composting. For a description of how to build your own bin or for a list of manufactured composting bins, visit our About Composting Bins page. In addition, see CalRecycle's Building You Own Composting Bin: Designs for Your Community guide.
Recipe for Composting
While the overall process involves a multitude of organisms, fungi, and bacteria, the composting recipe only requires four basic ingredients: nitrogen, carbon, water and air. Easy as baking a cake, blend roughly equal parts of green or wet material (high in nitrogen) and brown or dry material (high in carbon). After you chop or shred into short pieces, layer or mix these materials in a pile or bin and add water into the pile. Microorganisms break down the material over several months if the pile is turned weekly.
Nitrogen. Grass clippings, yard trimmings, and other green material are ideal sources of nitrogen for composting. Vegetable and fruit discards provide nitrogen, too. To prevent odors and eliminate pests, avoid meat or dairy scraps and bury food scraps deep within the compost pile.
Carbon. Dry leaves, twigs, or wood chips provide the carbon bulk needed for a compost pile. Use sawdust sparingly if the pile contains excess nitrogen.
Water. Microorganisms like moisture content at 40 to 60 percent and shut down when the pile gets, too dry or soggy. Your compost pile should be moist as a wrung-out sponge. Test for adequate moisture, reach into the pile, grab a handful of material (at least warm-to-the-touch if material is composting), and squeeze it. If a few drops of water come out, it probably has enough moisture. Water and turn the pile or place a hose into the pile so that more than the top gets moist, but not soggy. During dry weather, water regularly. A properly constructed compost pile drains excess water.
Air. Bacteria and fungi need oxygen to live and work. If your pile is too dense or soggy, the air is depleted of oxygen and the beneficial organisms die. Decomposition slows and an offensive odor arises. To keep the process aerobic, turn the pile with a pitchfork weekly. Many composting bins make this an easy task by coming apart so that you can re-pile the old pile back into the bin. More expensive bins rotate or roll to aerate the material inside.
Composting happens faster if actively managed or slowly in a casually monitored manner.
Given adequate mass and the right blend of nitrogen (greens), carbon (browns), moisture, and air, compost piles heat up to temperatures of 120 to 150 degrees Fahrenheit. These high temperatures kill most weed seeds and speed up the process to just a few months. Compost happens even if you just pile up yard trimmings and food scraps, water sporadically, and wait. Some of the pile won’t get as hot, decomposition slows over a longer time, and most weed seeds survive.
Ideally, the compost pile measures at least three feet wide by three feet deep by three feet tall (one cubic yard). This minimal mass provides enough insulation to maintain pile temperature produced by the organisms present. However, smaller or larger piles work just fine if managed well.
When Finished Product
You produce compost when the original material becomes a uniform dark brown, crumbly product with a pleasant earthy aroma. If a few chunks of woody material are left, screen these out and put them into a new pile.
Stop adding organic material to your compost pile after it gets to your optimal size (see the Time-Temperature Process above) and start a new pile. Allow your first pile to cure for a month and reach ambient temperature.
Through practice and observation, find what works best for your situation and needs. Since composting is a popular book topic, check your local library or bookstore. Remember to check with your local government for workshops, handouts, or guides on composting.
Composting Facility or Operation
California law defines a composting facility as a solid waste facility. Most composting activities on a small scale can be excluded from regulations or can be authorized with just noticing the local enforcement agency. Larger sites or ones handling food and other wastes from offsite sources may require a permit. For more information, please refer to Compostable Materials Handling Operations and Facilities Regulatory Requirements.
Composting regulations are established by CalRecycle and enforced by the local enforcement agency. There are other environmental agencies that may also have requirements for composting operations, such as the Regional Water Quality Control Board, the Air Quality Management District, the local planning department, and the local fire district. Information on how a composting activity of given size and feedstock fits into regulation, and what other licenses or permits are required, can be obtained by contacting your local enforcement agency.
Equipment and Cost
From a purely technical perspective, medium-scale composting offers opportunities and efficiencies over small-scale operations. However, while the fundamentals of composting remain the same whether it’s one cubic yard or 1000, certain management issues become more critical as volumes increase.
Managing a small home compost pile requires little more than a pitchfork. However, managing hundreds of cubic yards at a time may require heavy equipment. Small motorized loaders with a front bucket or blade, sometimes called skip loaders, are useful equipment for moving and lifting composting materials. Preprocessing larger trimmings will facilitate decomposition, so a chipper or grinder may be useful. In the process end, screening the compost separates larger pieces from the finer compost and creates a higher quality product. The larger pieces can be returned to the composting process, or further refined and used as mulch.
Clearly, the larger the operation, the more expensive it becomes. However, larger piles will decompose more rapidly than small, and a variety of different green material produces a more consistent product. The marginal costs of production—the dollars spent per ton of material—generally decreases as an operation grows. Additionally, the avoided disposal costs may justify the investment in equipment to manage large amounts of material.
Size and Temperature
Caution must be taken to avoid piling materials, too high or getting, too hot. While a hot pile is desirable to kill weeds and pathogens, temperatures should be managed and kept below 150 degrees Fahrenheit to avoid destroying beneficial organisms and control fire danger. With the right combination of ingredients and weather conditions, the danger of spontaneous combustion is very real if compost piles are allowed to stack much over ten feet high. The heat from microbes consuming the composting material will build up through a "chimney" effect. Once temperatures reach approximately 170 degrees, the microbes are killed off, but a biochemical reaction takes over that can eventually result in flames. The water vapor or steam released from an active, healthy compost pile should not be mistaken as fire.
Perhaps your landscaping activities generate more trimmings than you are able to manage or your own composting operation isn’t feasible. There are two good reasons to deliver materials to an organics recycler or composter instead of a landfill: (1) the "tipping fee" is usually less at a recycler’s operation than disposal and (2) the recycler has a supply of soil amendments that your clients can use.
If your local government doesn’t know of one, CalRecycle can help you find an organics recycler who will process your trimmings and also be a source of soil amendments for your landscaping projects.
Use this checklist to help you do your part by composting organic materials for yourself or your clients, or deliver your trimmings to a commercial organics recycler.
- Compost piles or bins are located in an area with easy access that is aesthetically acceptable.
- Compost ingredients are added and blended to balance nitrogen and carbon ratios. The right mix is equal parts "green" and "brown."
- The compost is kept sufficiently moist, like a wrung-out sponge.
- The compost pile is turned, fluffed, or aerated to provide oxygen to microbes and prevent odor.
- The finished compost is used as a soil amendment to return nutrients to the landscape and save money on amendment purchases.
- Diseased plant material and mature weeds with seeds should not be added to a pile.
- Large-scale composting must be performed in a responsible, good-neighborly manner.
- State and local laws require permitting or licensing of larger composting facilities.
- Take excess material to local, commercial-scale composters. They accept clean landscape trimmings and sell quality organic soil amendment for landscaping uses.