Composting and Mulching: A Guide to Managing Organic Yard Wastes

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Materials for Composting

Many organic materials are suitable for composting. Yard wastes, such as leaves, grass clippings, straw, and nonwoody plant trimmings can be composted. The dominant organic waste in most backyard compost piles is leaves. Grass clippings can be composted; however, with proper lawn management, clippings do not need to be removed from the lawn (see Alternatives to Composting Grass Clippings, page 12). If grass clippings are used, it is advisable to mix them with other yard wastes such as leaves or wood chips as a bulking agent to increase free air space. Otherwise, the grass clippings may compact and restrict air flow. Branches, logs, and twigs greater than 1/2-inch in diameter or more than 8 inches long should be put through a shredder/chipper first. Kitchen wastes such as vegetable scraps, fruit waste, coffee grounds, and eggshells may also be added. Some cities have ordinances that restrict the use of food scraps in compost piles. Check with local authorities about restrictions in your area.

Because they may pose a health hazard or create a nuisance, certain organic materials should not be used to make compost. Adding human, cat, or dog feces cannot be recommended because they may transmit diseases. Meat, bones, grease, whole eggs, and dairy products should not be added because they can attract rodents to the site. Most plant disease organisms and weed seeds are destroyed during the composting process when temperatures in the center of the pile reach 130-150 degrees F for 15 days or longer. However, in most home compost piles, it is very difficult or impossible to mix Materials for Compostingefficiently enough to bring all wastes to the center. Consequently, adding large amounts of weeds with seeds or diseased plants may create problems if the compost is used in the garden.

Sawdust may be added in moderate amounts up to a maximum of 10% of the total pile volume, if additional nitrogen is applied and free air space is adequate. Approximately 1-1.5 lb. of actual nitrogen (6-9 cups of ammonium nitrate) is required for 100 lbs. of dry sawdust. Wood ashes act as a lime source and if used should only be added in small amounts (no more than 1/2 cup per five gallon bucket). Excessive amounts of wood ashes will result in loss of nitrogen from the pile. Ordinary black and white newspaper can be composted; however, the nitrogen content is low and paper will therefore slow down the rate of decomposition. If paper is composted, it should not be more than 10% of the total weight of the material in the compost pile. We recommend recycling newspaper through appropriate community recycling centers rather than through backyard composting.

Examples of other organic materials that can be used to add nutrients, especially nitrogen, to the pile include cotton seed meal, blood and bone meal, livestock manure, and lake plants.

Avoid composting plants that have been treated with herbicides or pesticides. Small amounts of herbicide-treated plants (e.g., grass clippings) may be mixed in the pile as long as you are careful to let them decompose thoroughly. Studies have shown that low levels (less than 0.1 parts per million) of 2,4-D, diazinon, and pendimethalin can be detected in well-composted yard trimmings². This level, however, is less than 1% of the level typically found in yard waste mixtures prior to composting and is not considered a risk for using in the garden. Ideally, clippings from lawns recently treated with herbicides should be left on the lawn to decompose (see section on Alternatives to Composting Grass Clippings). Both pesticides and herbicides are degraded at varying rates. A list of common chemicals used on the home lawn and their degradation rate in soil is provided in Table 1. Even if some treated grass clippings are used, the degradation of these chemicals in a properly maintained compost pile should be at least as fast as that in the soil.

Composting Structures

To save space, hasten decomposition, and keep the yard looking neat, it is recommended that the compost pile be contained in a structure. Composting structures can be made of a variety of materials and made as simple or complex as desired. There are many options available that can be tailored to individual needs. Listed below are a few suggestions for containing the compost.

A barrel or drum composter generates compost in a relatively short period of time and provides an easy mechanism for turning (Figure 1). This method requires a barrel of at least 55 gallons with a secure lid. Be sure that the barrel was not used to store toxic chemicals. Drill six to nine rows of 1/2-inch holes over the length of the barrel to allow for air circulation and drainage of excess moisture. Place the barrel upright on blocks to allow bottom air circulation, fill it three quarters full with organic waste material, and add about 1/4-cup of a high nitrogen containing fertilizer. If needed, apply water until moist. Every few days, turn the drum on its side and roll it around the yard to mix and aerate the compost. The lid can be removed after turning to allow for air penetration. Ideally, the compost should be ready in two to four months. The barrel composter is an excellent choice for the city dweller with a relatively small yard.

      Figure 1

Bin-type structures are the most practical for larger quantities of organic waste. For example, a circular bin can be made by using a length of small spaced woven wire fencing and holding it together with chain snaps (Figure 2). The bin should be about four to five feet in diameter and at least four feet high. A stake may be driven in the middle of the bin before adding material to help maintain the shape of the pile and to facilitate adding water. With this design, it is easiest to turn the composting material by simply unsnapping the wire, moving the wire cylinder a few feet, and turning the compost back into it.

      Figure 2

A three-chambered bin is a very efficient and durable structure for fast composting (Figure 3). It holds a considerable amount of compost and allows good air circulation. The three-chambered bin works on an assembly line idea, having three batches of compost in varying stages of decomposition. The compost material is started in the first bin and allowed to heat up for 3 to 6 weeks. Next, it is turned into the middle bin for another 4 to 8 weeks, while a new batch of material is started in the first bin. Finally, the material in the middle bin is turned into the last bin as nearly finished compost and left to cure until finished composting, usually an additional 5 to 16 weeks.

      Figure 3

To make this structure, it is best to use rot-resistant wood, such as redwood or cedar, or a combination of wood and metal posts. Unless the wood is rot resistant, it will decompose within a few years. Each bin should be about five feet by three feet and about four to five feet high. This volume is ideal for maintaining heat and at the same time is manageable for turning. Using removable slats in the front offers complete access to the contents for turning.

There are many other structures for composting, and no one structure is best. Invent your own, or for a more thorough description of different structures, refer to Rodale's Complete Guide to Composting^4. If you don't want to build a structure, there are several commercial composting units available through local garden stores or mail-order catalogues. Make sure that these units meet the minimum size requirement of one cubic yard or larger in size so that you have a large enough mass to self-heat to 130 degrees F-150 degrees F.

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