1. Particle Size
  2. Temperature
  3. Humidity
  4. pH
  5. C/N ratio
  6. Aeration
  7. Microbe growth

There are a number of factors that need to be adjusted for the optimum quality and production time. Missing any one of of the above determinant composting factors will limit the effectiveness of the natural process taking place.

Compost Component Particle Sizes

All particles sizes need to be as small as possible. In a lengthy, natural process in the forest the particles are all shredded by larger macro-organisms like arthropods. But these larger insects we want to keep out of our pots… besides it takes months for them to shred plant materials. A small particle size gives easy access to the bacterias and fungus for molecular bond division. These two microorganisms will be breaking down the material by depositing digestive enzymes on the surface of the components. Bacteria and fungus do not have mouths. The material will need to be pre-digested for the microbes to absorb them into their tiny bodies. The materials we use for our high nitrogen compost at Organic Soil Technology comes to us inherently small particle sizes except for our sugar cane stalks.  The cane is already smashed and broken for microbe easy access but a last shredding is done. Our other components of rice hulls, manures and rice meal are already shredded giving them a large enough surface area for microbe access. Small particle sizes create more surface area. Surface area is an important component when we are talking organic technology. Surface area influences not only compost temperatures and rates, surface areas influence pot-substrate water retention and cation exchange capacity’s for nutrients.



Open air composting is an aerobic exthermo-biological reaction where temperature moisture and air all effect each other. Therefore proper temperature is important as heat is released in the procedure. You will find different recommended temp targets depending on which University’s information you are studying. But here at OST we maintain a higher temp than most recomendadtions. In our view high temperatures of between 65C and 75C should be maintained during the thermophilic stage. The major reason for high temperatures is to rid the materials of pathogens, live seeds and macro-organisms. The reason for keeping the compost below this range is because at higher temperatures there is a loss of nitrogen in the form of ammonia from vaporization when the C:N ratio is low.

The C:N ratio also effects the temp. Too much carbon and your target temp might never be reached. So a drop in temperature when the compost is still young means the pile is becoming anaerobic. Anaerobic decomposition is a much cooler process. The pile will need aeration when the temp drops to get air to the aerobic microorganisms at work.

As you can see monitoring the temperature during the process can tell you a lot. The temp should reach 70C within 2 to 3 days. Monitoring the temp throughout the composting will give you a good idea just where the composting process is. There will be different temps in the pile due to surface area loss and aeration. So go deep into the pile for readings.

Sanitation | Lethal Compost Temp Specs

Sanitation of the compost will take effect for different microbes at different temps and temp durations.

  • Viruses 1-2 hrs at 55 to 70C
  • Non-spore-forming bacteria 5 to 30 min at 50 to 60C
  • Spore forming bacteria 5 to 10 min at 121C
  • Fungus 1 to 2 hrs at 55c



We need to keep the humidity percentage at about 60%. An anaerobic process will take over if the humidity is higher. Microorganisms use water to move around as well. If the humidity is not high enough the decomposition process will slow down. Here at OST we add water that is mixed 30% with molasses. In this way we distribute the simple sugar for microbe energy as we maintain the humidity needed. The moisture, molasses and an even spray of microorganisms in liquid solution is added in the beginning as the compost pile is built. Moisture will evaporate as the weeks progress so adding water during aeration is required as well.


Monitoring pH

The pH of your compost is not something that is adjusted. The pH changes with time so it is something that is monitored as the composting process is working. You can measure the pH at any time during the composting but remember that activity and therefore pH will vary depending on the depth of the sample. The closer to the center the hotter it will be.      So samples at different locations will be necessary if you are really intent on knowing what is going on.

In the beginning stages of decomposition, organic acids are formed, such as humic, acetic, butyric, lactic and propionic acids. This will give the compost a 5-6pH level. Initially, the acidic conditions are favorable for the growth of fungi and therefore the breakdown of lignin and cellulose. As the composting continues the organic acids should end up becoming neutralized. This gives bacteria a chance to do it’s work. But if anaerobic conditions prevail, organic acids may accumulate rather than decompose. This will halt or slow the composting process dominated by bacterias. Aerating or mixing the compost pile should reduce this acidity. Adding lime in the form of calcium carbonate will decrease acidity but that would vaporize nitrogen in the form of NH4+ and this would lower the final nitrogen content of the compost.


Carbon Nitrogen Ratio


For all the interesting info on the Carbon Nitrogen Ratio, refer to its post.