When most people think of compost, they tend to simply think of it as an organic material that is added to their garden beds to help
nurture plant growth. The science behind composting isn't too difficult to understand, but you do need to have more than a slight
interest in composting to actually realize what is happening within the compost pile. Throughout the different stages of the decomposition process,
compost is literally teeming with millions of microorganisms. These microorganisms will vary in population density and type depending on which
stage or phase your compost pile is in.
Composting Phases
- The Mesophilic Phase
- The Thermophilic Phase
- The Maturation Phase
Mesophilic Phase
The mesophilic phase is the first phase of the decomposition process during which the specific mesophilic bacteria and fungi start to
degrade the soluble organic materials within the compost pile. For a few days, the temperature of the pile will remain in a moderate
range until microorganism activity starts to increase. As the process continues, the 'breaking down' of the proteins within the compost
will cause ammonia to be released and the soil pH of the pile will spike
to approximately 9. All of this activity building within the compost will cause the temperature to start rising. The mesophilic phase
will usually last a few days.
Thermophilic Phase
The thermophilic stage commences when the temperature of the compost reaches approximately 113°F. As the temperature continues to rise
to this stage of the process, the mesophilic bacteria will cease activity and thermophilic bacteria will take over and continue
degrading the organic waste. An ideal temperature to attain during the thermophilic phase is roughly 140°F to 160°F as increasingly higher
temperatures will tend to start limiting the high rate of decomposition within the compost and start destroying some thermophilic
microorganisms. The thermophilic phase will last anywhere from just a few days to several months, depending upon many different
factors. Human and plant pathogens are destroyed during the thermophilic phase of decomposition.
Maturation Phase
Once the thermophilic microorganisms have depleted the supply of proteins, fats and complex carbohydrates, mesophilic microorganisms
return to finish, or mature, the compost. Not to be confused, there is considerable difference in the makeup of the microorganisms
inhabiting the compost during the initial mesophilic phase and the latter maturation phase. This phase will result in degradation of
residual gases and other compounds that were formed during the high heat conditions of the thermophilic phase.
