Introduction
The most widely used vermicomposting system, worldwide, is the ‘bed’ method, which involves applying thin layers of sanitised and partially matured compost, to the surface of beds containing high densities of earthworms. New layers of waste are applied to beds on a regular basis and the earthworms move upwards into the fresh waste to feed and to process the material. Earthworm numbers increase as more waste is applied until a limiting density is reached.
Harvesting earthworms by hand
The earthworms are then harvested or the beds are divided.
Harvesting earthworms by hand can be a very time consuming business and although in principle trommel screens would be suitable, these are seldom used. The top 100 mm to 150 mm of the compost bed soil is removed regularly and is the worm compost sold. How long does it take to make mature vermicompost? It is difficult to compare directly composting with vermicomposting in terms of the time taken to produce stable and mature composted products.
With vermicomposting, particles of waste spend only a few hours inside the earthworm’s gut and most of the decomposition is actually carried out by micro-organisms, either before or after passing through the earthworm. Hence, earthworms accelerate waste decomposition rather than being the direct agent. With windrow composting, it usually takes at least six to twelve weeks to produce a stable compost, and research suggests that vermicomposting takes about the same length of time.
Processing rates will depend on many factors
However, processing rates will depend on many factors such as the system being used, the nature of the wastes and the ratio of earthworms to waste.
Ingredients Composting organisms require four equally important things to work effectively:
- Carbon — for energy; the microbial oxidation of carbon produces the heat[citation needed]. High carbon materials tend to be brown and dry.
- Nitrogen — to grow and reproduce more organisms to oxidize the carbon. High nitrogen materials tend to be green (or colorful, such as fruits and vegetables) and wet.
- Oxygen — for oxidizing the carbon, the decomposition process.
- Water — in the right amounts to maintain activity without causing anaerobic conditions. Certain ratios of these materials will provide beneficial bacteria with the nutrients to work at a rate that will heat up the pile. In that process much water will be released as vapor (“steam”), and the oxygen will be quickly depleted, explaining the need to actively manage the pile.
The hotter the pile gets, the more often added air and water is necessary; the air/water balance is critical to maintaining high temperatures (135°-160° Farenheit) until the materials are broken down. At the same time, too much air or water also slows the process, as does too much carbon (or too little nitrogen). The most efficient composting occurs with a carbon:nitrogen mix of about 30 to 1. Nearly all plant and animal materials have both carbon and nitrogen, but amounts vary widely, with characteristics noted above (dry/wet, brown/green).
Fresh grass clippings have an average ratio of about 15 to 1 and dry autumn leaves about 50 to 1 depending on species. Mixing equal parts by volume approximates the ideal C:N range. Few individual situations will provide the ideal mix of materials at any point in time – in this respect, home composting is like horseshoes, perfect is great, but close still works. Observation of amounts, and consideration of different materials as a pile is built over time, can quickly achieve a workable technique for the individual situation.
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