As a follow up to the vermicompost (worm composting) post the other day, today’s post delves into outdoor composting. While similar in their goals, vermicompost and outdoor compost bins have radically different requirements. As suggested by the name, outdoor compost bins require access to the outdoors so that naturally occurring microorganisms can populate the compost pile. In contrast to vermicompost, the microbiotic organisms enter the pile from the atmosphere. Some inoculant – a small amount of soil containing bacteria and other decomposers – is added during the process.
According to the Environmental Protection Agency, food scraps are the third most common type of waste in the US. Along with yard waste, they constitute roughly 20% of landfills by volume. Nationwide, this adds up to approximately 52 million tons of waste annually. In order to divert some of this material from the waste stream, individuals can compost their food and yard waste. By doing so, homeowners can reap the benefits of mimicking natural systems as opposed to chemical inputs (as discussed in an earlier post comparing the first and second green revolutions) and helping to close the loop by returning matter into the nutrient cycle.
Composting has a number of other benefits. The reduction of waste sent to the landfill results in lower tipping fees, potentially reducing strain on city budgets. A byproduct of decreased landfill dumping is reduced methane production. While this gas can be captured and burned, it is not necessarily a sustainable method of energy generation, as mentioned in an earlier post.
What follows is a basic version of the steps to ensuring a healthy compost pile. These are taken from Denver Urban Gardens’ compost demonstration site at Colorado Blvd and 13th Ave in Denver.
How to compost
- Build pile nearby composting material
- Choose an area that is level and semi-shady
- Build pile in layers with about 60% mixed carbonaceous (such as chopped wood or dried out leaves) material and about 40% mixed nitrogenous (such as food scraps or grass clippings) material (by volume) – until you have reached three feet wide, by three feet deep, by three feet high
- Sprinkle on some soil or finished compost. Mix layers well.
- Add water – pile should feel like a wrung-out sponge.
- Cover pile with black plastic tarp or straw.
- Temperature of pile should rise to about 120 deg F in 3 days and to about 140 deg in another 3-4 days
Having worked on several piles at the demonstration site last year, it is amazing how hot the compost gets within a few days. In addition, some of the piles shrunk by 80%, reducing down to a mere fraction of the starting cubic yard. The resulting compost, which forms in 6-8 weeks and is ready after another 6-8 weeks of curing is not as rich as the vermicompost. However, there are fewer challenges than maintaining my underground compost bin.
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