   Garden Composting - December 29, 1999 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Much of what goes into our trash cans, and ultimately into our sanitary landfills, can be composted. Homeowners commonly recycle kitchen wastes, weeds, grass clippings, leaves, small twigs, and other yard debris into compost. Newspapers, hair (from pets and haircuts) and the contents of vacuum cleaner bags can also be composted. In fact, almost anything that was once living is a candidate for composting. There are major exceptions to this rule. Grease, oil, meat scraps, human and pet excrement should NOT be added to garden compost. Composting requires some basic knowledge about the organisms that will perform the task of decomposition and their basic needs. These micro and macro organisms are your work force. If you take care of them, they efficiently convert the waste materials into rich humus. The most critical factor for successful compost is the ratio of carbon to nitrogen (C:N) in the raw materials. A C:N ratio of thirty parts carbon to one part nitrogen is ideal. Tables containing C:N ratios of various raw materials are available from the Arizona Cooperative Extension office. The proper amount of moisture is also important. Too much moisture will prevent oxygen exchange and too little will not provide favorable conditions for the organisms to thrive. Carbon is the main constituent of organic matter. Plants take in carbon dioxide during photosynthesis and incorporate it into cell walls, proteins, sugars, nucleic acids (DNA and RNA) and lipids (fats and oils). Just as we consume foods and convert them to carbon dioxide through respiration, organisms in the compost pile use the organic residues that you add to your compost. Although nitrogen is needed in smaller quantities, without it the compost will not decompose. Nitrogen is a major constituent of protein and nucleic acids. Most backyard composters use manure, green plant residues, or nitrogen fertilizers to bring nitrogen into balance with the carbon. The microorganisms that get the process started are in the air and soil. By adding small amounts of topsoil to your compost, you can inoculate the pile. The organisms living in the compost use both carbon and nitrogen to grow, reproduce, and grow more. Once their populations increase, they begin to break down the organic matter more quickly. A food chain (or a food web) with many different organisms feeding on the raw materials and each other lives within the compost pile. Fungi, bacteria, actinomycetes, insects, and worms feed on the raw organic matter. Springtails, mold mites, beetles feed on the fungi. Protozoans, roundworms, rotifers, and other small organisms graze on bacteria. Larger insects such as centipedes, solpugids, beetles, mites, and flat worms feed on the smaller organisms. All the organisms produce waste and/or die to create the compost. It's a real jungle in there. When I compost at home, I use three-foot high wire fencing and form a six-foot circle. The first layer is a 10" thick layer of straw, leaves, or freshly pulled annual weeds. To this I add a four-inch thick layer of horse manure. I top this off with dusting of my best garden topsoil. I repeat the process three times and add just enough water to moisten the ingredients and wash the topsoil downward. It gets really hot (140 degrees F) in two or three days and maintains this for a week or so. The compost will need turning after a couple of weeks to mix the materials on the outer edges into the center of the pile. Just undo the wire fence and move it to an adjacent location, then fork the compost back in. Add water if it seems dry. Kitchen scraps can be buried in the surface of the pile. At my house, we have a half gallon plastic bucket with a lid for kitchen wastes. To this we add vegetable wastes, leftover cereal, moldy bread, and thing else that we can catch (except grease and oil). We even add leftover coffee and tea (liquid, grounds, and leaves). This provides liquid and would just be added to our septic system so why not add it to the compost. I am also a homebrewer and the spent grain from the mash is an excellent addition. A compost pile that is not working is either too dry, too wet, or lacking sufficient nitrogen. A compost pile that smells like ammonia has too much nitrogen. In any case, you can add the appropriate materials and get it cooking again. Sometimes when it slows down, I add a pinch of ammonium sulfate. It works wonders. Many people have toys that they use to make and monitor their compost. These include shredders, thermometers, manufactured bins, and handy gadgets to help you turn it. I hope this helps you get started composting. Heck, it may even inspire you to start homebrewing. The University of Arizona Cooperative Extension has publications and information on composting and cover crops. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 or E-mail us at mgardener@kachina.net and be sure to include your address and phone number. |