Elements of “Fast” or “Hot” Compost Piles (Also Known as “Batch” Piles)
When an environment is favorable for any species to sustain life, that species will reproduce rapidly until the environment begins to decline. The more decomposers eating your organic waste, the more quickly you will produce finished compost. Our goal is to create the most favorable environment possible so that decomposers multiply quickly, as is the case with the fast compost process in a hot compost pile, also known as a batch pile.
NOTE: Heat may not be desirable if you are composting with a specific decomposer, (e.g., grubs, red wigglers or other earthworms). Instead, you will want to buy or make a container that meets the habitat needs of that specific decomposer.
For compost piles in Compost Bins on CompostMania and tumblers, the hot batch process creates an ideal environment to attract fast-acting aerobic bacteria. They reproduce so quickly that the center of a hot compost pile will initially reach 140 to 170 degrees Fahrenheit. As it is maintained over 8 weeks, the pile will attract many additional decomposers including bacteria, fungi, insects and macroorganisms such as worms, mites, and sowbugs.
A hot batch environment provides optimal levels of four basic needs:
1) Mass. For a fast compost pile to heat properly, it must be large enough that outer portions of the pile provide insulation for the hot center. The minimum mass desired is 3’x 3’ x 3’. Compost piles that are smaller than this will not heat up well, and may not heat up at all.
For a home composting pile, the maximum desirable size is 4’ x 4’ by any length (known as a windrow). If you build larger than this, you run the risk of having the pile attract anaerobic bacteria unless you upgrade to large-scale equipment and methodologies.
2) Food. Organic waste provides food for decomposers. We are primarily interested in two food groups: nitrogens and carbons. A waste is considered a nitrogen if its nitrogen content is higher than its carbon content. If the carbon content is higher than nitrogen content, it is considered a carbon.
There is a popular terminology referring to nitrogens as “greens” and to carbons as “browns.” This can be confusing since color has nothing to do with it. Here are a few rules of thumb for differentiating between the two:
Nitrogens include wastes that rot quickly and therefore are more likely to produce a strong odor if not aerated. Nitrogens typically have higher water content. Nitrogens include grass clippings, manure, flat beer, fizzed-out soda, coffee grounds, tea grounds, fresh non-woody plants, flowers and garden wastes.
Carbons include wastes that rot more slowly. They would burn easily due to their low water content. High-carbon wastes include material that is woody in nature such as twigs, wood chips and pine cones. Carbons also include dead leaves, straw, newspaper, cardboard, sawdust, pine needles, sawdust, prunings, tree bark and tumbleweed.
3) Water. Organic wastes such as coffee grounds and manure may already have a high moisture content. However, you will usually need to add more water to the pile as you build it. The dampness of your batch pile should be equivalent to that of a wrung-out sponge (i.e., when you squeeze a handful of it, one drop may fall). As materials decompose, water will be depleted by decomposers, by wind, and by evaporation. So remember to water again every time you turn the pile.
4) Air. Organic waste should be added loosely to your fast compost pile, not compacted down, so that many air pockets exist. As materials decompose, these pockets will collapse. In addition, decomposers will deplete the air supply over time, so you will need to turn the batch pile to reintroduce more air into it.
The steps in How to Build a HOT Compost Pile incorporate guidelines that allow you to achieve these four crucial elements in a home composting pile or bin composting environment.
Mary Tynes, Master Composter, www.mastercomposter.com
Image credit: http://www.flickr.com/photos/superfantastic/4123518950/