Originally Published: June 13, 2014 6 a.m.
Composting reduces the amount of material going into our landfills. Twenty to 40 percent of the solid wastes currently entering landfills could be composted. In addition, compost enhances soil fertility, increases water holding capacity, and adds humus, which provides nutrients for plants. If you keep this material on-site (i.e. on your property), then it also reduces transportation costs and lengthens the usable life of sanitary landfills.
Composting is a microbial process that converts plant materials such as yard trimmings, grass clippings, leaves, safe animal manures, coffee grounds, vacuum cleaner contents and kitchen scraps into a beneficial organic soil amendment. Gardeners have used compost for centuries to increase soil organic matter, improve soil physical properties, and supply most of the essential nutrients for plant growth.
Composting is both art and science. The "science" is well documented and resources are available at Cooperative Extension offices, libraries, and on the Internet. The "art" is making it practical and easy given your individual household, landscape/garden, and waste products generated. If you only have a few annual flowerbeds and do not vegetable garden, you can compost kitchen scraps and yard wastes on a small scale. If you are vegetable gardener, you should make as much compost as possible - our summer temperatures and alkaline soils cause it to decompose quickly.
Composting is not as complicated as it seems. It need not smell bad, attract vermin, or take too much time.
The critical factors in composting are maintaining: 1) an appropriate (about 20:1) carbon-nitrogen ratio by weight; 2) good aeration; and 3) adequate moisture. You should never add human/dog/cat waste, meat products, bones, dairy products, oil, or grease to your compost. The trickiest part is the carbon-nitrogen ratio. Green materials and manure contain relatively large amounts of nitrogen. Brown materials such as straw, pine needles, twigs, sawdust, wood shavings, and other non-green materials are almost entirely carbon. This means about 20 parts brown material to one part green waste or manure.
When the carbon-nitrogen ratio is near 20:1, the compost will get warm and smells sweet like leaf mold. This ratio is ideal for decomposing bacteria and fungi. They utilize the carbon and nitrogen by incorporating it into their cell structure, increasing their populations which, in turn, speeds the decomposition process. When finished, the bacteria and fungi have slowed down, leaving behind nutrient rich compost. When there is too much carbon, compost decomposes very slowly and it does not rise in temperature. When there is too much nitrogen, the compost will smell like ammonia. You are in control and can add appropriate materials at any time to adjust the ratio and shift the activity to create a proper balance.
Adequate aeration ensures that aerobic conditions predominate. A lack of aeration can create anaerobic conditions which lead to a stinky, unsavory compost pile. Straw, twigs, and pine needles can increase aeration or a few lengths of 4 inch perforated drainage pipe can be strategically buried in the pile to allow oxygen in the atmosphere to reach the inside of the pile.
Moisture is relatively easy to maintain once adequate aeration is achieved. Compost should be kept as moist as a wrung-out sponge. In Arizona, compost tends to dry out too quickly. For this reason, I recommend a compost bin with solid (not ventilated) sides. I just have simple galvanized sheet metal to contain my compost pile. If you turn the contents of the pile every two to three weeks, it will compost faster. If you don't turn the pile, but keep it moist and have the proper ingredients, you will have compost in six months.
Composting is very forgiving - when things are out of balance, you can readjust your compost by adding materials or increasing aeration.
You can visit with a Master Gardener volunteer at the University of Arizona Cooperative Extension office on the Prescott Rodeo Grounds at 840 Rodeo Dr. #C, 9 a.m. to noon and 1 to 4 p.m. Mondays through Fridays. Call 928-445-6590, ext. 224, for more information.
Jeff Schalau has been the Agriculture and Natural Resources Agent with the University of Arizona Cooperative Extension, Yavapai County, since 1999.