Hands sift through compost ready for use

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. Click any item below to learn more about elements of the compost environment important for rapid, efficient composting (show all items).

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.

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.

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 degrees F for three 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. If your pile does not heat up, don't worry: Compost Happens! at all temperature levels.

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.

Carbon to Nitrogen Ratio

For composting, scientists target a carbon-to-nitrogen ratio of 30 to 1 (30:1), as measured on a dry-weight basis. This is known as the C:N ratio, and it can be easily calculated. Take an example where a composter starts with two bags of grass clippings, each with a C:N ration of 20:1. That person also has a similarly sized bag of leaves, which has a C:N ratio of 60:1. Combining the content of the three bags would result in a mix very close to the ideal ratio:

(20:1 + 20:1 + 60:1) / 3
= (100:1) / 3
= 33:1

The following chart lists the C:N ratios for many common composting materials:

MaterialC:N Ratio
Coffee grounds 20:1
Corn stalks 60:1
Feces/manure, cow 20:1
Feces/manure, horse (with litter) 60:1
Feces/manure, rotted 20:1
Fruit wastes 35:1
Grass clippings 20:1
Leaves 60:1
Newspaper 50-200:1
Oak leaves (green) 26:1
Peat moss 58:1
Pine needles 60-110:1
Sawdust 600:1
Sawdust, two-month weathered 325:1
Straw 80-100:1
Table scraps 15:1
Vegetable trimmings 12-20:1
Wood 600:1

Don't get bogged down in the numbers, though. What's important is to understand how greens and browns affect the compost process and to use them to manage your compost system.

All plants have more carbon than nitrogen. That is why the C:N ratio is always greater than 1:1. Materials, like wood chips, that are rich in carbon but low in nitrogen are known as "brown" materials. At the other end of the spectrum, materials, like grass clippings, that have a lower C:N ratio are called "green."

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 stress over the C:N ratio. Just understand that it might be a factor in your composting process.