Get Composting - November 19, 2008
Jeff Schalau, Associate Agent, Agriculture & Natural Resources
University of Arizona Cooperative Extension, Yavapai County

You are not a real gardener unless you compost its just that simple. Composting need not smell bad, attract vermin, or take too much time. Twenty to forty percent of the solid wastes currently entering the landfill could theoretically be composted and used to enhance soil fertility, increase water holding capacity and reduce soil surface erosion. If you keep this material on-site (i.e. on your property), then it also reduces transportation costs and would lengthen the usable life of sanitary landfills.

Composting is a microbial process that converts plant materials such as grass clippings, leaves, 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 some of the essential nutrients for plant growth.

Composting is an 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, and gardening interests. 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 enough compost to cover the soil of your garden plot with three inches deep every year.

The critical factors in composting are maintaining: 1) a 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 wastes and manure contain relatively large amounts of nitrogen. Straw, pine needles, twigs, sawdust, wood shavings, and other non-green materials are almost entirely carbon.

When the carbon-nitrogen ratio is near 20:1, the compost will get warm and smells sweet like silage or 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 and speeding the decomposition process. The bacteria and fungi die, leaving behind nutrient rich compost. When there is too much carbon, compost decomposes very slowly. 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.

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, shavings can increase aeration or a few pieces of 4 inch perforated drainage pipe can be buried in 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 humid areas, compost gets too wet and bins are designed to dry out quickly. Conversely, 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 bins in my garden.

During the fall season, we often have lots of leaves. Rather than burning or bagging them, compost them. As stated above, leaves are mostly carbon and will need an addition of nitrogen-containing materials to begin composting. Grass clipping are an ideal nitrogen containing material, but are not usually available in large enough quantities to compliment huge amounts of leaves. In these cases, you may also use a nitrogen containing fertilizer to make up the difference. Just make sure you layer the leaves and nitrogen fertilizer to ensure the nitrogen is available throughout the compost pile.

Remember that composting is an art and science. It is very forgiving when things are out of balance you can readjust your compost by adding materials or increasing aeration. For more composting information, I have provided some on-line resources with the web-based version of this column. Several previously published Backyard Gardener columns also contain lots of composting information. I encourage you to dig deeper on the subject of compost!

The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site:

On-Line Composting Resources

Composting and Mulching: a Guide to Managing Organic Yard Wastes (Univ. of Minn. Cooperative Extension)

Cornell Composting (Cornell Waste Management Institute)

Texas A & M University Composting Resources

Composting at Home (Ohio State University Extension)

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Arizona Cooperative Extension
Yavapai County
840 Rodeo Dr. #C
Prescott, AZ 86305
(928) 445-6590
Last Updated: July 16, 2009
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