The general guide followed by many composters today is to use equal amounts of “Greens” and “Browns” and excellent compost can be made just by having a basic understanding as to whether the materials
being added to the bin are Greens and Browns. This knowledge need to be supplemented with an understanding of how to correct the balance if the bins turn out to be too wet or too dry.
To recap on the earlier page Greens
are those materials that are rich in nitrogen, decompose quickly and provide protein to the microorganisms involved in the composting process. Nitrogen is a crucial component of the proteins, nucleic acids, amino acids, enzymes and co-enzymes necessary for
cell growth and function
Browns are carbon rich materials that are slower decomposing and the carbon is the basic building block provides a source of energy and growth it makes up about half of the mass of microbial cells.
This page provides a little more detail on the Carbon: Nitrogen ratio and lists a range of Greens and Browns in order of their Carbon content. I must stress that compost will still be produced if the C: N ratios of the
bins are outside the recommended range. However, it is not just a question of getting the right C: N Ratio. All living organisms require moisture and the moisture level in the compost heap or bin should be between 40-60%. If below 35 to 40%, the rate
of decomposition will slow and below 30%, to all intents and purposes the decomposition process will stop. The bin will then offer a warm and dry housing opportunity to rats and other creatures. If the materials are too dry, the problem can be easily
rectified by adding more Greens, compost/comfrey tea or water.
If waste food and plenty of Greens are added to the pile too much moisture is more likely to be the problem. If the mixture is, too wet air may not penetrate
the wet acidic (see Compost pH) contents with the main microbial activity to be by anaerobic organisms, resulting in the wet and smelly bin that puts so many composters
55% to 60% is the usual recommended upper limit for moisture content. If it is too wet, extra carbon rich materials can be added to deal with this problem. Turning the contents as the additional
Browns are added will also make more oxygen available encouraging aerobic decomposition. In the worse cases, the bin can be emptied and fresh Browns mixed into the wet mass and the bin refilled. Browns with a high C: N ratios such as wood chip
or straw are very useful in such cases.
Too much circulating air , or prolonged hot sunlight can make the pile or bin too dry for fungi, bacteria and other decomposers to work effectively. Inadequate moisture
levels are the more common problems found with home composting.
During the summer, it may be necessary to add water to the bin, even if the C: N ratio is within the recommended range, to compensate for that lost
due to the heat from the sun and evaporation. This is particularly likely to happen with some of the smaller plastic bins.
The C: N ratio and moisture are not the only factor to consider. Compost organisms need oxygen, and
larger particles help maintain an aerobic environment by increasing airflow in the compost. Woodchip and wood pellets are excellent at increasing the available air in the compost bin (and make excellent bulking agents when composting cooked food waste)
scrumpled paper and kitchen roll tubes provide air pockets, Jerusalem Artichoke and other hollow stalks also provide a useful means of providing air pockets. If woodchips are used, there are advantages in watering the material before adding it to the bin,
as they do not absorb moisture as readily as paper or leaves. Many composters will add shredded paper or leaves to the woodchip to assist moisture retention in the compost bin.