Some books about composting give the impression that compost piles must be built according to a particular recipe. They suggest that a pile must be arranged in precise layers of specific materials for decomposition to proceed effectively. This impression is misleading. No single formula provides effective decomposition. Assorted ingredients and varying amounts of intervention on your part will all result in compost.
Design a compost pile that reflects your purpose and your willingness to manage the process. If you’re not in a hurry, you can throw material into the pile haphazardly. If you’re interested in fairly rapid decomposition and high internal temperatures to kill weed seeds, then design the pile with deliberate attention to the carbon-nitrogen ratio. Achieving roughly equal amounts of carbon and nitrogen is easier if you build the pile all at once. Although layering is traditional, mixing the materials actually works better. To produce a pile that will heat up in less than a day, run alternating handfuls of nitrogen and carbon materials through a shredder as you build the pile.
You can arrange the materials in layers if you wish. The tiers should be between 2 and 6 inches thick. Within that range, the material will heat up in the same amount of time. As you build the pile, whether you do it gradually or all at once, don’t compact the materials in an effort to get more into the composting area. Air is essential to the decomposition process, and compressing the pile just reduces the available air supply and slows decomposition significantly.
Managing the Carbon-Nitrogen Ratio
For home composters, accurate calculation of the carbon-nitrogen ratio of a compost pile is virtually impossible—there are too many variables. However, after you’ve had a year or two of experience making compost, you’ll know when you’re on target.
The subtlety of carbon-nitrogen ratios is important only if you’re producing compost quickly and want as much nitrogen as possible in the finished product. The difference in the nitrogen content of a compost that decomposed slowly over a year or longer and a compost made carefully but quickly is relatively small. Slow compost protected from the weather may contain between ½ and 1 percent nitrogen; quick compost made with attention to the carbon-nitrogen ratio may contain 2 percent nitrogen.
Feel confident that you’re managing the ratio well if you use roughly equal volumes of carbon and nitrogen materials. If the pile heats up well and doesn’t smell bad, you’re pretty close to right.
Managing Particle Size
The decomposition rate increases as the size of the organic materials decreases. If you don’t care about the rate of decomposition, then you can just throw whole, uncut materials into the pile. But if you want the pile to decay faster, take the time to chop up large fibrous materials, such as cornstalks and broccoli stems.
Exclude woody materials if you’re not chopping or shredding them, since they take much longer than other organic materials to decay. This is especially important if your compost bin doesn’t allow you to pull finished compost from the bottom. Even if there is access space at the bottom, twigs and branches tend to block the way, making the removal of compost a real nuisance.