Creating and managing our compost doesn’t have to be complicated. There are a few key components to a successful and healthy hot-compost pile. An easy way to share and highlight the components of successful composting is by using the acronym C.O.M.P.O.S.T as a memory tool.
Carbon (browns) and Nitrogen (greens) are both critical elements of healthy compost. Carbon is an abundant, naturally occurring element that forms the basis of most living organisms. Nitrogen is a gaseous element that exists in plant and animal tissues and is released in decomposition. For use in our hot compost system the suggested ratio is 25 to 30 parts carbon to 1 part nitrogen.
What makes our hot composting system successful, effective and (nearly) odorless is the presence of huge amounts of bacteria and microorganisms that break down the organic waste material aerobically. In order for these organisms to thrive and proliferate they need access to oxygen which is maintained through aeration. Aeration can be accomplished by making sure your compost container can breathe using holes, slats or pipes that allow air flow. Turning the compost is also a form of aeration and mixes oxygen into the system.
The bacteria and other organisms breaking down our compost need moisture to to function. Dry conditions can slow down, or stop, biological activity by making it impossible for our bacteria to move or consume anything. To wet and our bacteria can suffocate. Ideally, our compost system wants to maintain a moisture content somewhere around 50%. Think about a wet sponge that has been wrung-out, it’s still moist but not dripping wet.
The size of the material we add to our compost can also be important to how well it functions. The bacteria working in our compost don’t have the ability to chew and break apart materials. They need smaller pieces to maximize surface area they can eat more, faster. At the same time, we need to have some larger materials in our compost for structure. This creates air pockets for oxygen and keeps the compost from compacting.
How our compost smells is a key indicator of how healthy it is. A healthy compost pile should smell like rich, earthy soil. A sour or foul ammonia odor coming from the compost is an indicator that something is out of balance, usually too much moisture (creating an anaerobic condition) or too much green material. In general, the problem is solved with more brown material, aeration (turning) and less water.
There are a lot of determining factors in where we want to locate the compost pile and it usually deals with convenience, personal preference and exposure. In colder climates where it might be difficult to keep compost warm, a southern exposure where the bin can get some sun could be advantageous. In the southwest, a shaded spot will help keep it from drying out or getting too hot. Also consider locating it with easy access to inspect and maintain the bin, close to a water source so we can maintain moisture, and possibly near the garden where it will be easy to use the finished compost.
The temperature of our compost pile determines how quickly and how completely the decomposition process happens. Colder piles will still decompose but they will take much longer and may not completely break down invasive seeds and pests. Ideally we want the center of our compost pile to maintain a temperature between 150 and 120 degrees Fahrenheit. To maintain this optimal temperature range, we must maintain proper carbon:nitrogen ratios, good moisture and turn the pile on a regular basis for aeration.
Click here to download a printable PDF of this for use in the Lab.
The acronym C.O.M.P.O.S.T. is used to illustrate the components of a successful compost system in the Minibook Urban Composting Made Easy by Southwest Urban Farmer and Master Gardener Kari Spencer.