Backyard Composting Basics
Nature has been composting since the beginning of the earth. All organic matter eventually breaks down. Composting in your backyard uses the same principles that nature uses - we just try to speed it up by creating an environment that supports microbial activity. The elements necessary to promote this environment are:
Adding air means adding oxygen to your pile. Microbes need oxygen to break down material efficiently. Under ideal conditions they work hard and reproduce quickly depleting oxygen in the pile.
You can aerate your compost pile by turning it or probing it with an aeration device and adding bulky items such as straw or chipped twigs. Bulky items also keep the pile from compacting and restricting oxygen flow.
Your pile should be kept slightly moist (not wet). You can compare this to a damp sponge. If the pile is too wet it will compact down and restrict airflow. This slows down the process and causes a foul odor. If your pile becomes too wet, turning it will help dry it out.
It is a good idea to reduce the size of the composting materials before you place them in the bin. Smaller materials have more surface area available for microbes to attack. Materials such as twigs should be chipped to a size of 2" or less before composting.
Carbon to nitrogen ratio
The ideal ratio of carbon to nitrogen is 30 to 1 (30:1). This is simply the balance between greens and browns. Carbon supplies energy in carbohydrates and nitrogen provides growth in proteins. All living things need these elements to survive and they use roughly 30 parts carbon to each 1 part of nitrogen. If too little nitrogen is present in the pile, not enough heat will generate. If too much nitrogen is present, it is released into the air as ammonia and can cause odor problems. Don't worry too much about the C:N ratio, just remember this is a factor in the composting process. You don't have to be precise in making your pile, just try to use approximately 60% browns to 40% greens.
The optimum temperature for fast decomposition is between 90 and 135° F. When microbes flourish, they raise the temperature of the pile. It is necessary for a pile to reach a temperature of 131° F for 3 days to destroy weed seeds or plant pathogens. If your pile does not heat up, your compost pile will still break down, but at a slower pace. The higher temperatures are also a deterrent to the attraction of rats or other unwanted vermin.
For hot/fast composting you need a minimum of 1 cubic yard of material to start a pile. The ideal volume for fast composting is 3' long x 3' deep x 3' high.
If you feel you do not have enough material to start a hot/fast compost pile, a pile can be started with a smaller amount, however, it will not heat up until you have more volume. For example, a small amount of leaves, twigs or garden debris can be placed in a pile. Do not start a bin or pile with green/nitrogen material only (such as grass clippings) or you could end up creating an anaerobic condition and a smelly mess. Food waste should always be buried under carbon material such as leaves, newspaper, sawdust or straw to deter rodents.