Since compost happens automatically in nature, composting is a very forgiving art. With enough time, any organic material will break down into stable finished compost. There are many techniques, however, to make this process quicker, safer and more pleasant.
A good compost pile is built with a proper nitrogen ratio in order to provide a good environment for the decomposition organisms. High nitrogen materials such as kitchen scraps, animal manures and grass clippings must be combined with high carbon materials such as autumn leaves, wood chips, or straw.
The best compost is made with a carbon nitrogen of 30 parts carbon to each 1 part nitrogen. If this ratio is too high, decomposition can slow down and you may end up with a less fertile compost. If the C:N ratio is too low, your compost pile will stink much worse.
In casual terms, high nitrogen materials are refered to as “greens” and high carbon materials as “browns.” Good compost building is about combining the proper ratios of greens to browns.
Carbon:Nitrogen Ratio Chart
Ratios of Common “Green” Materials
- Kitchen Wastes: 15:1
- Grass Clippings: 19:1
- Rotted Manure: 20:1
- Coffee Grounds: 20:1
Ratios of Common “Brown” Materials
- Leaves 60:1
- Straw: 80:1
- Paper: 180:1
- Wood Chips: 300:1
Some people weigh and calculate the proper amount of greens to browns using a C:N ratio chart like this one. For example, if you the average family, you produce 10 pounds of kitchen scraps per week. Food scraps have a C:N ratio of 15:1 and if we are using leaves at a carbon ratio of 60:1, we know that we will need to add 5 pounds of dry leaves weekly to create good compost.
I don’t generally recommend this detailed algebraic approach to building a compost pile, and this is where the “art” of compost comes in. For the average compost at home, or even the more professional compost system on a larger scale, I recommend my own method – the “smell test.” Carbon materials work so quickly in soaking up odor that once properly mixed and combined with smelly nitrogen materials, the smell will vanish nearly instantaneously. Stop adding carbon materials at this time, or you risk adding too much carbon, which is actually less of a problem than not adding enough.
It is important to know the approximate ratios, so you know to use far less wood chips than you would straw for example. However, your nose is a better tool for building the properly proportioned compost pile than a calculator.
There are many methods of combining the greens and browns together, each with its advantages, disadvantages, and rabid fan bases. Some of the most popular composting methods for home are the cold compost and the batch compost, but we will discuss all current popular methods of composting on this site.