Backyard Composting: Turning Trash into Treasure

In Alabama, a family of four generates an average of 2.5 tons of garbage per year. Twenty percent of the solid waste produced annually in Alabama is composed of lawn and garden debris such as grass clippings, tree and shrub trimmings, leaves, and kitchen wastes. Fortunately these wastes contain materials ideal for backyard composting.

Why compost? Compost acts as wonderful mulch and a great slow-release fertilizer for trees and shrubs as well as vegetables and bedding plants. Compost tilled into a sandy soil can improve the soil’s water and nutrient holding capacity, and when added to a clayey soil, improves drainage and soil aeration. Above all it is an inexpensive and environmentally friendly way to recycle yard and garden wastes, cut down on landfill overcrowding and reduce waste disposal costs.

The key to effective composting in the home landscape is to regulate the conditions under which microbial decomposition takes place. Microbial conditions must be just right – a balance of air, water, carbon, nitrogen, and temperature - for rapid and effective decomposition to occur.

Let’s begin with air. Composting is an aerobic process requiring oxygen to occur. Compost piles can receive oxygen in two ways: by turning the compost pile and by constructing the pile so surface air can diffuse into the center. Too little oxygen in a compost pile can result in offensive odors. Microorganisms also need water to survive and function properly. Moisture content of a compost pile should be between 40 and 60 percent. The compost should be moist when squeezed but not dripping wet.

Materials high in carbon and nitrogen provide food sources for the microorganisms. Carbon (C) sources (carbohydrates found in plant residues) supply energy while nitrogen (N) sources (manures, kitchen scraps, nitrogen fertilizers) provide needed protein. The ratio of C to N is important for microbial growth and to prevent odors from forming. An optimum C:N ratio is about 30:1. Surface area can also be a factor in this relationship because carbon in leaves is much more available than the carbon in a large wood chip. Small chips give more surface area on which to feed. A leaf shredder or chipper is useful for preparing an efficient compost pile.

Temperature is another important factor. Microorganisms generate heat as they grow and multiply. The heat helps destroy many kinds of weed seed and disease organisms, however if temperatures rise above 140° F, beneficial microorganisms begin to die. Turn the pile when temperatures reach this point to prevent overheating and speed up the entire process.

Determine your type of system by how well you will be able to manage the compost process. Cages, piles, or turning units are popular choices. When building and managing your compost pile, the important thing to remember is to follow the correct layering sequence. Construct a compost pile in layers, alternating yard wastes, a nitrogen source, if needed, and soil or finished compost. Begin with a 6-inch layer of coarse materials such as small twigs or branches then place finer materials such as leaves or grass clippings in a layer about 6 to 8 inches deep. If using high carbon materials such as wood chips, add 1 cup of commercial fertilizer such as 10-10-10, 10-6-4, or 13-13-13 or manure. The final layer consists of soil or finished compost 1 to 2 inches deep. Repeat the sequence of layers but omit the coarser material with subsequent layers.

What can you add to the pile? Almost any plant waste can be added to the compost. Kitchen scraps such as vegetable and fruit scraps, egg shells, and coffee grounds can also be added but make sure to bury in the pile to avoid odor. DO NOT add meat scraps, bones, or fats because they will attract unwanted animal and insect pests.

Turn to mix the compost periodically, ideally after the temperature in the middle of the pile has reached 140° F, to encourage uniform aeration of the pile. Add water if the pile dries out. Compost is ready to use when it looks like a uniform potting soil (dark colored and crumbly) with little distinguishable evidence remaining of original materials. For more information on composting contact your local Extension office or visit our online publication at http://www.aces.edu/pubs/docs/A/ANR-0638/ANR-0638.pdf.