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Composting in Urban Areas

By John Pohly, Colorado State University Cooperative Extension agent, horticulture

No time to compost? Don't think it's important?

You may want to think again.

That yard waste -- leaves, grass and dried plant debris -- may one day have no place to go, if landfills become full and close. Then composting will sound like a terrific idea.

News such as this should be just what you need to begin a compost program. It will help you save on your trash bill and you'll recycle organic matter that doesn't need to go to the dump in the first place.

A lot of waste can go into a compost pile, including food scraps from the kitchen, such as vegetable and fruit waste, bread, pasta and similar materials. From the yard, you can bring grass clippings, tree leaves and weeds that haven't developed seeds. Twenty percent of your compost pile can be shredded newspapers.

Maintained properly, compost isn't dirty and smelly. If composting is done correctly, it can occur in the average city neighborhood without offending anyone's senses.

Mother Nature provides the three ingredients needed to begin composting -- nitrogen, oxygen and moisture.

NITROGEN

The micro-organisms that break down compost need nitrogen to do the job. Green plant materials, such as grass clippings, contain nitrogen; so do manures, from leaf-eating animals. (You also can get nitrogen from chemical fertilizers.) Pet waste, from dogs and cats, is not recommended because of the possibility of transmitting diseases or parasites to humans.

Too much nitrogen, however, and the compost pile smells of ammonia; too little and the microorganisms will not be able to do their job.

OXYGEN

A compost pile also needs oxygen. If making a free-standing compost pile, this isn't much of a problem. You must mix the compost to keep it from packing and excluding air. Do this by turning the pile upside down or by using aerating tools that you can buy for this purpose.

If making compost in a container, you'll need to be sure the container has plenty of airholes to supply oxygen.

MOISTURE

Additional moisture is a must because of Colorado's arid climate. The correct moisture content for the compost is about the same as a damp sponge. Too wet and the compost won't get enough oxygen. (Pore spaces for air will be filled with water and the compost will smell sour.) Too dry, and the microorganisms won't work.

As organic materials decompose, they give off heat. Temperatures in a compost pile can reach 150 degrees F. to 160 degrees F, if the pile is working properly. The pile should be at least three feet high and five feet wide to maintain the volume necessary for adequate moisture and heat retention.

What should you do if your landscape won't produce this volume of materials? You may want to purchase a manufactured compost bin that allows the composting of smaller volumes of materials.

For faster decomposition, reduce all materials going into the compost to their smallest possible size. This means chopping or shredding larger materials. Unless you can reduce tree limbs to chips, don't use limbs in the compost.

Photograph courtesy of Judy Sedbrook.

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Date last revised: 01/05/2010