Written by Diana McGinn, Certified Master Gardener since 2022
I have been trying to have a successful backyard open compost bin for a couple of years. I like the idea of taking advantage of natural processes to divert a small amount of organic waste from going into our landfills, where it decomposes without oxygen, creating methane gas. Plus, I know the decomposed organic matter came from plant materials that I added and that the finished material can be safely added to my garden beds when the process is complete, gradually improving the growth potential of the soil.
As described in the references listed below, there are many science-based studies written that describe the biological and chemical processes that occur as carbon materials are broken down and that also prescribe the best practices for the ideal open compost pile. Basically, this process utilizes a variety of naturally occurring microorganisms which digest organic matter, in the presence of water and oxygen. A different type of successful composting can also be done using worms (vermicomposting). Since this requires a different setup, it will be discussed in a future newsletter.
Inedible parts of a wide variety of common fruits and vegetables are compostable. To facilitate the process, it is important to provide a mix of brown (dry) and green (wet) organic matter. The best ratio is approximately 2 parts brown to 1 part green. Common examples of brown organic matter (OM) include dead leaves, dried plants, dead grass, straw, or small amounts of shredded plain paper (not glossy). Common examples of green OM include vegetable or fruit waste, eggshells, immature weeds, coffee grounds, and untreated grass clippings. The wet and dry OM can be mixed together or added in layers. It also speeds the decomposition process if the added OM is chopped into smaller pieces. The pile needs to be kept watered to the wetness of a “wrung-out sponge” and mixed periodically (recommended weekly, if possible).
Materials that are NOT compostable in the backyard include pet waste, meats and oils, plants with seeds or diseases, large amounts of grass, especially if the lawn has been treated recently with pesticides/herbicides. Backyard compost piles do not reach a sufficient temperature to kill seeds or any disease-causing organisms and it is best to avoid the potential of later adding chemicals to garden beds where food is grown.
Other considerations are where to locate the pile, how big the pile should be, and whether a structure is needed to contain the material. A containing structure is often used just to prevent material from blowing around and to assist with maintaining the pile size and shape. The structure can be made out of a wide variety of commonly available material such as pallets, scrap lumber, wire, or cinderblocks. The are also commercially available barrel units that are self-contained and can simplify many of these decisions.
The basic size of the pile should be a minimum of 3 ft. x 3 ft x 3ft. This size facilitates the higher internal temperatures needed for the decomposition process. If you have large amounts of material seasonally (i.e. fall leaves), you can create more than one bin and have piles at different stages of decomposition.
Also important, is locating the pile in a convenient location that is accessible for adding and removing material and within easy reach of the hose. As mentioned, the ability to keep the pile damp is critical for this process. If you live on the windy, hot-summer Front Range, it helps to locate the pile in part shade and protect it from the wind to reduce the need for constant water. If you live at higher elevations, there may be less need for shade and wind protection.
To improve conditions for my composting efforts, this spring I moved my compost pile to the east side of a shed, where it gets afternoon shade and protection from the west winds and it is also near a newly transplanted tree seedling that needs extra water, so it is easy to water the pile at the same time. So far, the change seems to be helping. I turned the pile recently and there was a lower layer of brown, crumbly OM, indicating the composting process is working! I will plan on mixing the finished compost into the existing soil in my raised beds this fall.
CMG Fact Sheet #7.212 Composting Yard Wastes
CMG Garden Notes #246 Making Compost