•Active or Thermophilic Phase - This is the phase when the most rapid breakdown of materials occurs. After the materials are mixed and the pile is created, temperatures rise above 45ºC and decomposition starts. The micro-organisms use oxygen to consume the materials and respire carbon dioxide. Temperature and moisture beyond the optimum ranges (40-60ºC, 50-60% moisture) or low oxygen levels will reduce biological activity. High moisture levels reduce oxygen. Low moisture levels can result in temperatures rising too high. The time required for the active phase will depend on the materials, ambient air temperatures, and the composting method. In-vessel systems with turning and aeration can offer the shortest times.
•Curing or Mesophilic Stage - After the main thermophilic phase, most materials have broken down and are not recognizable from their original form. Temperatures are more stable (usually less than 40ºC) even after the pile is turned. In this stage there is a shift in the organism populations to those that prefer lower temperatures. Turning is not needed but compost should remain aerobic. In the curing phase, compost is not yet mature. Immature compost may have higher levels of organic acids, high C:N ratios, extreme pH values or high salt contents - all of which can damage or kill plants. The time to cure may vary up to a year but is generally less than 3 months.
•Maturing Phase - compost needs time in storage to mature. Maturity is indicated by the degree of humification or the conversion of organic compounds to humic substances that are resistant to microbial breakdown. There are various tests for compost maturity. Lab tests can be used or germination tests using lettuce or cress seeds can be used. Immature compost may injure the germinating seeds and plants will not survive. During the maturing phase, pile size is less critical than during the active or curing phases.
How to Achieve Success: √ Balanced Carbon & Nitrogen
A C:N ratio ranging between 25:1 and 30:1 is the optimum combination for rapid decomposition
Carbon: When plants die, they end with high carbon content and are the "brown” components that are added to compost. Decomposers consume the protein-rich tissues first and disperse the nitrogen in the form of dead bacteria, bug droppings, ammonia and other by-products leaving only carbon behind which is why it takes longer to decompose.
Nitrogen: Living things have a high nitrogen content – they are the "green” components that are added to compost. Manure is considered a green material because it stays rich in nitrogen for so long. Fresh grass cuttings, vegetable peels, and other food scraps are also nitrogen rich.
√ Adequate Moisture and Oxygen √ The Right Particle Size √ A Healthy Temperature
Just as carbon and nitrogen must be balanced, so must moisture and oxygen. Too much moisture leaves no air space, but too much ventilation dries out the materials. Early in the composting process, the main difficulty is keeping all the materials in a well-mixed pile moist— damp to the touch, but not "wet”. Later, as they break down into a crumbly, more absorbent, compact mass, the main challenge may be to keep the material aerated with fresh air. Rapid composting at high temperatures can deplete oxygen in the pile quickly, even early in the composting process.
Composting happens where moist organic materials are exposed to air. When materials are broken down into small particles, there is more exposed surface area for composting organisms to attack. Microscopic organisms penetrate solid objects slowly.
The best way to know whether your compost is healthy is to take its temperature. Composting occurs most efficiently when the pile’s temperature rises to between 40 to 60 degrees Celsius and stays there until most of the material has decomposed. As the material decomposes, it cannot support as many bacteria. As the bacteria decreases, the temperature gradually drops.