How Composting Works


Composting occurs as a natural process when bacteria, fungi, insects and other organisms decompose waste and convert it into a soil amendment. The waste products provide the organisms with food. A compost pile or bin must have aeration, moisture and a balance of carbon and nitrogen. The combination of these causes the compost to heat and initiate the process of decomposition. Special containers for composting are widely available, but a simple pile also works.


Fruits and vegetable trimmings, coffee grounds, crushed egg shells, leaves and garden waste compost readily. Avoid composting any diseased plants or weeds that have formed seeds. Tree and shrub trimmings decompose slowly unless shredded. Do not compost dairy, animal waste or meat products, including bones. These items attract pests and will slow the composting process. All materials decompose more quickly when chopped into small pieces.


A balance of materials provides the best results when composting. A compost pile needs brown materials high in carbon and green materials high in nitrogen. Aim for a carbon/nitrogen ratio of 25:1 to 30:1. Carbon materials include leaves, straw and pine needles. Nitrogen materials tend to hold moisture, such as grass clippings, rotted manure, fruit wastes and table scraps. Keeping the nitrogen materials to about a quarter of the total materials is a simple way to maintain balance.

Air and Water

The organisms that break down the waste products require oxygen and water. Provide aeration through layering the materials and turning the compost. Some items, such as leaves, form mats and need to be broken apart for proper air flow. Keep the moisture content between 40 and 60 percent. Too much water suffocates the good bacteria and too little water causes them to go dormant. Allow access to rain, or water the compost to provide moisture. Covering the compost during heavy rain or wet seasons prevents it from absorbing too much moisture.


You can use finished compost for numerous garden applications. It works as a mulch, soil conditioner and fertilizer. Compost will improve drainage and fertility when worked into poor soil. It balances the soil pH. Compost combined with other materials, such as perlite, makes a potting mix for container plants. To use compost as mulch, spread a 3-inch layer over garden beds. If amending the soil, the 3-inch layer needs to be worked into the top eight inches of soil. A light top dressing throughout the year provides a dose of nutrients similar to fertilizer.

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About this Author

Kit Arbuckle is a freelance writer specializing in topics such as health, alternative medicine, beauty, senior care, pets and landscaping. She has training in landscaping and a certification in medicinal herbs from a botanical sanctuary.