Consider Composting - February 17, 2016
Jeff Schalau, Agent, Agriculture & Natural Resources
University of Arizona Cooperative Extension, Yavapai County


Composting is a critical link in the home gardening chain. It 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. Compost enhances soil fertility, increases water holding capacity, and adds humus. 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, leaves, safe animal manures, coffee grounds, vacuum cleaner 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 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, materials available, and interests. If you only have a few annual flowerbeds and do not grow vegetables, 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 disappear quickly.

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 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.

When the carbon-nitrogen ratio is near 20:1, the compost will get warm and smells sweet like leaf mold. The 20:1 ratio is an ideal substrate 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 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 humid areas, compost gets too wet and bins should be designed to allow some drying (woven fence wire). 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 for my compost.

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 clippings 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. Adding small amounts of soil to these layers will inoculate the compost with locally-adapted microbes.

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 resources below.

Follow the Backyard Gardener on Twitter use the link on the BYG website. If you have other gardening questions, call the Master Gardener help line in the Camp Verde office at 928-554-8992 or e-mail us at verdevalleymg@gmail.com and be sure to include your name, address and phone number. Find past Backyard Gardener columns or provide feedback at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/.

Additional Resources

Composting and Mulching: a Guide to Managing Organic Yard Wastes
University of Minnesota Extension

extension.umn.edu/how-manage-soil-and-nutrients-home-gardens/composting-home-gardens

Making and Using Compost
University of Missouri Extension

extension.missouri.edu/p/G6956

Composting for the Homeowner
University of Illinois Extension

web.extension.illinois.edu/homecompost/intro.cfm

Home Composting
North Carolina State University Extension

content.ces.ncsu.edu/backyard-composting-of-yard-garden-and-food-discards

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Arizona Cooperative Extension
Yavapai County
840 Rodeo Dr. #C
Prescott, AZ 86305
(928) 445-6590
Last Updated: August 23, 2018
Content Questions/Comments: jschalau@ag.arizona.edu
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