Elements of Composting

Rapid composting requires an environment in which microorganisms will thrive. To compost well, you must "think like a microbe" and create the best environment to support microbial activity.

Microbes have similar environmental needs as people: water, air, comfortable temperatures, and food. The elements of the compost environment that are important for rapid, efficient composting, include:

	Moisture
	Aeration
	Pile temperature
	Particle size
	Carbon to nitrogen ratio

Moisture

Microbes need moisture to thrive. At the ideal moisture level, 40-60%, a handful of compost will feel wet but water cannot be squeezed out of it. Some people compare this to the feeling of a damp sponge.

It may be necessary to add water to the composting system to keep it moist.  Add water when building and turning the compost pile.

Compost should be kept moist, but not soggy. If the materials are too wet, they will compact and restrict the airflow through the pile. This leads to anaerobic (no oxygen) conditions, which slow down the degradation process and causes foul odors. A pile which becomes too wet should be turned. Turning the compost will dry it out and add oxygen. 

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Aeration

Aeration means adding oxygen to your compost system. Microbes need oxygen to break down organic materials efficiently. Because they reproduce so quickly under ideal conditions, microbes may deplete the available oxygen through their activity. Therefore, it is important to aerate your compost.

You can aerate your compost by turning it. This directly incorporates oxygen into the pile.

You can aerate by adding bulky items. Bulky items provide air channels so that oxygen can flow into and through the compost. Bulky items also keep the pile from settling and compacting, which could restrict oxygen flow. Bulky items include oak leaves, pine needles, chipped twigs, and straw.

You can aerate by probing the pile with a piece of rebar or an aeration tool. Simply probe the devise in several places in the pile. This will create passageways for air to enter the pile.

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Pile Temperature
Compost pile temperature is a function of the biological activity within the composting system, and, to some extent, its exposure to the sun. When microbes flourish, they will raise the pile temperature through their metabolism, reproduction, and conversion of composting materials to energy.
The main reason to be concerned about pile temperature is that maintaining a minimum pile temperature of 131°F for 3 days is desirable to destroy weed seeds or plant pathogens. To establish this highly efficient biological system requires the proper food balance (a mixture of nitrogen and carbon rich materials), sufficient pile size (approximately one cubic yard), oxygen and adequate moisture content (moist but not soggy).
Your composting system may not reach higher temperatures during the composting process (see Troubleshooting - Pile too Cool). If your pile does not heat up, don't worry: Compost Happens! at all temperature levels.  Compost thermometers are available for measuring compost temperature.

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Particle Size
Smaller materials have more surface area available for microbes to attack. Therefore, reducing the particle size of raw materials will increase the speed of the composting process. Size reduction also reduces the volume of the compost pile, thereby saving space.
	It is a good idea to chip or mulch small limbs and twigs to a size of 2-3 inches before composting.
	Particle size can be too small. For example, sawdust sized and wet materials can decrease aeration, reduce the rate of composting and perhaps cause anaerobic conditions leading to odor problems.

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Carbon to Nitrogen Ratio

Scientists speak of an ideal ratio of Carbon to Nitrogen of 30 to 1 (30:1), as measured on a dry weight basis. This is known as the C:N ratio. But DON'T GET CAUGHT UP IN THE NUMBERS. What's important is to understand how greens and browns affect the compost process and to use them to manage your compost system.

You can calculate the C:N ratio of your materials by using the chart below.  For example, if you have two bags of grass clippings (C:N = 20:1)  and one bag of leaves (C:N = 60:1) then combined you have a C:N ration of (20:1 + 20:1 + 60:1)/3 = (100:1)/3 = 33:1, which is pretty close to the ideal (C:N = 30:1).

You may also use the Virtual Pile, which will calculate C:N ratios for you.  If you have a slow connect speed, the Virtual Pile may take a minute or two to load.

Note that all plants have more carbon than nitrogen; that is why the C:N ratio is always above 1.0. Grass has a great deal more nitrogen than wood chips, thus it is called a "green" material. Wood chips are very high in carbon, but low in nitrogen. Thus they are called a "brown" material.

All plant material contains a mixture of Carbon and Nitrogen, and all plant material will compost over time. You will find the right mix of materials for your composting needs by trial and error. Don't worry so much about the C:N ratio, just understand that it can be a factor in your composting process.

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