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Composting Principles

Composting Principles was written many years ago by Bob James and was previously only available as a downloadable white paper. We have now made it accessible to all as an article. You can read it in conjunction with other composting articles. This will give you a greater understanding of composting and the many varied ways you can compost. Plus new easier ways to compost to suit more people especially those who failed at composting. We hope that the easy methods will generate more interest in composting among people. The more we all compost the less pressure we place on the environment and reduce council waste. In addition this produces less methane and nourishes your garden all at the same time. This article relates to all the traditional methods of composting and does not take into account composting with Soldier Flies

You can read this article on Composting with Black Soldier Flies either now or after you read Composting Principles.

Composting Principles

By: Bob James
(Q.D.A.H.,D.App.Sc),B. App.Sc(Hort Technology),Grad Dip. Mgt.,M. Sc( Enviro,Sc), Permaculture Design Cert J.P.(Qual)
Edited by: Victoria Brun
© Direct Compost Solutions

The Australian Brush Turkey has used heat from composting organic matter to incubate their eggs since time memoriam. Other names include Scrub Turkey, Bush Turkey or Wild Turkey. The male does all the work after the hen lays the eggs then walks away. He uses his very sensitive face to detect the exact temperature of the pile. Then he adds more organic matter to increase the temperature, or to rake away some material to lower the temperature. They knew about composting long before man used it to their advantage.

These days, people use composting to dispose of waste and improve poor soil. It also serves as a method to decontaminate soils that contain simple contaminants like low Carbon oil. This process utilises available fungi to break down organic pollutants into basic Carbon Dioxide and Water. These elements are then released into the air. It’s important to note that composting does not break down more complex Organic Pollutants.

History of composting

People have been using composting since as early as AD 23. The farmers of the day left organic matter on top of the soil until the next season of planting. By then it had broken down into the soil where it naturally improved the soil. They did not know the chemistry of composting back then. Just that it worked and kept the soil fertile for the next years planting.

Organic matter will hold nutrients and water for plants to access. It is therefore even more important to recycle nutrients back into the soil. Thus composting converts plants into improved soil.

Australians throw out an estimated $8bn worth of food each year. Throwing out food waste is not just throwing away the food itself. But also the energy that has gone into growing, processing, storing, refrigerating and transporting it.

Landfill areas in any large cities are rapidly filling up with our waste. Household organic waste is usually half the volume of all household waste. The estimated of waste is 631 kg per household per year. Add commercial organic waste to that and we have a huge problem. We need to divert waste back into our soil instead of landfilling it. Especially because Australia is the driest continent in the world.

Estimates suggest that Australians throw out approximately 4.9 million tonnes of food each year.

So why waste this great nutrient source by sending it off to the council tip. Much better to dispose of it in your own backyard. Nourish your own soil and reduce the environmental damage caused by large council waste sites. The production of methane from council tips harms the environment more than CO2.

What are the benefits of composting

  • – Improve drainage in clay soils and help sandy soils retain water and dissolved nutrients
  • – Helps plants grow stronger cell walls to resist diseases and insect attack
  • – Decrease runoff and thus decrease pollution of local watercourses
  • – Reduce council waste and associated Council disposal costs for your rubbish.
  • – Reduced greenhouse gasses
  • – Methane & carbon dioxide created in land fill areas are the result of anaerobic composting . i.e.. Composting without air. Aerobic composting (with air) is more common in the home garden. Thus less harmful to the environment.
  • Reducing the use of artificial fertilisers. Composted material is as good if not better and cheaper as well.

There are quite a few different methods to compost organic material but all have the same basic components of needing some Carbon rich material (eg. dead plants, especially dead leaves) plus some high Nitrogen material (eg. fresh grass clippings) and some naturally occurring Bacteria, Fungi as well as some small animals (eg. worms, cockroaches, lizards, etc). Without constant reduction of our organic waste by microorganisms, the world would be smothered in organic matter as it builds up day by day.

There are more micro-organisms in a teaspoon of soil than there are humans on the planet.

Conditions required to Compost

Nearly all composting methods need all of the following conditions in various amounts and combinations for composting to occur. The better the conditions the faster composting will occur. The conditions are:

  • A. Plenty of Organic Matter, for energy for the decomposing organisms
  • B. Nutrients, especially Nitrogen
  • C. Oxygen, (with a few commercial exceptions)
  • D. Water, but not too much nor too little
  • E. Cations, especially Calcium to stabilise the compost
  • F. A suitable pH range
  • G. Temperature

(A) Organic Matter

To achieve good results in a reasonable time, it is necessary to reduce any organic matter of plant or animal origin to bits smaller than 5-10 cm before using them for composting.

Items you CAN add to a compost heap:

  • – Vegetable and food scraps
  • – Leaves (eg in autumn from deciduous plants), soft stems, dead flowers
  • – Tea leaves and tea bags, coffee grounds
  • – Vacuum cleaner dust – Old potting mix
  • – Used vegetable oil – Egg shells
  • – Old newspaper (wet and shredded)
  • – Grass clippings, weeds without any seeds or other propagation material (especially Nut Grass ‘Nuts’), wood ash, human and animal hair
  • – Saw dust (except from CCA treated timber)

Items you CAN NOT add to the compost heap:

  • Diseased plants
  • – Metals, plastics, glass and other NON–compostable materials
  • – Fat, bones
  • – Magazines (these are too thick unless broken down or shredded)
  • – Larger branches (again good if reduced in size)
  • – Saw dust from CCA TREATED timber pine logs
  • –‘Coppers logs’ (CCA -Copper, Chrome, and Arsenic)
  • – Meat & dairy products (these will attract rats, mice and dogs and cats
  • – either yours or the next door neighbours), bread or cakes (these may attract mice or rats-either native or domestic). Animal manures (especially droppings of cats and dogs as these could have parasites in them and they stink too)
  • – Weeds with seeds or underground stems (eg. nut grass ‘nuts’). They will propagated when the compost is used
  • – Sharp or thorny plants as these probably will not have broken down by the time your compost is ready to use.

There are plenty of bacteria, fungi and Actinomycetes (a major group of fungi that do a lot of the decomposing) so adding “Compost Activators” is of no benefit as there is a vastly larger number and variety already in the air, soil and Organic Matter (OM).

Maybe, if you think it needs it, you can add some old compost so the bacteria, fungi & Actinomycetes already in the compost will act as a starter source when dug into the new composting heap.

What is the best ratio of Carbon to Nitrogen?

The table below gives you an idea of Carbon and Nitrogen contained in some materials

Leaves 0.7 % NC/N 60:1 & water content is about 20%
Weeds 2% NC/N 19:1 & water content is about 80%
Poultry Manure 2.5% NC/N 10:1 & water content is about 30%

Water content can be estimated by:

Fresh plants85-90% water
Lawn clippingsC/N 20:1 and 85% moisture
PaperC/N 170:1 and 10% moisture
Cattle droppingsC/N 12:1 and 50% moisture
Fruit wasteC/N 35:1 and 80% moisture

Water content may also be estimated by:

  • – If you can just squeeze water from a material then there is about 60% water in it
  • – If it feels like a squeezed–out sponge then it has about 55% water
  • – Sun dried for a few days will leave about 10% water but
  • – If lying around and not in the sun, it will have about 20-40% water

Adding sawdust and bark

Sawdust and barks are commonly used in composting. They contain compounds in them, some of which are easily composted. Eg. Sugars and starches from inside cells and cellulose from cell walls, but others, eg. Lignin from cell walls, are a lot harder to compost

Ideal size of a compost heap

The ideal size of a compost heap is 1 m as this will allow the heap to heat up enough to kill any insects and weed seeds in the middle. Turning every 3-4 days by moving the outside cooler material to the inside and the hot inside material to the outside, allows the pile to cool down and not overheat which can, in very dry hot areas, can cause the pile to catch alight.

Orgainc matter

Organic matter in a compost heap needs to be as small a piece as practical (usually 5-10 cm) as the smaller the material then the larger the surface area for the microbes to work on to reduce the material. This holds especially true for newspaper and cardboard that remains in large sheets. It will mat together and give poor aeration. A commercial shredder will achieve this result for you in your backyard or even just running over the heap with a mower will cut up the material and be almost as good.

Animal manures

Different types of animal manures are available. People often mix the manure with bedding when they clean out animal housing areas. The mixing of manure with bedding depends on factors such as the frequency of cleaning out animal housing areas, the type of animals housed in the shed, and the type of bedding used. Eg. Straw, sawdust, or non-traditional materials like newspaper, or chopped cardboard.

When mixing manure with bedding, cattle and horse manure result in good compost. Pig manure is typically wet, and not mixed with bedding. It needs to be combined with straw or a similar product to lower its water content. Nonetheless, the strong odor associated with pig manure often makes it unsuitable for use.

When obtaining horse or cow manure, exercise caution. Feed lot waste often contains chemicals used in the growing process of the that feed. The animals pass these chemicals in their waste. Composting does not destroyed these chemicals. Potentially they cause harm to your plants. Read this newsletter on poison in horse manure: https://directcompostsolutions.com/composting-horse-manure-BEWARE

Due to its high nitrogen content, it is necessary to mix poultry manure with a high carbon material like sawdust.

Human waste

Collecting human waste (such as from composting toilets) typically involves letting it sit and cure for a year or more, resulting in a dry, nitrogen-rich product. Moreover, it often contains a significant amount of fiber from the paper and/or sawdust used.

When adding Humanure (a mixture of human waste and manure) to soil, it retains the majority of the nutrients. These are nitrogen, phosphorus, potassium, carbon, and calcium. Thus they are not lost to the sewage system. Additionally, this approach avoids any loss of potable water.

Humanure kills most pathogens and parasites by both the heat generated and the long time it is left to compost (usually up to two years)

(B) Nutrients

A lot of written information recommends that Calcium be added to compost so it is not too acidic. But most compost is close to neutral with a pH of about 7 when mature, being neither acid nor alkaline. Calcium comes in many different forms.


By adding lime (calcium carbonate – which comes from finely ground up limestone) or dolomite (lime plus magnesium – naturally occurring so can vary) will increase the pH of your compost pile making it alkaline. Making the compost pile alkaline causes a chemical reaction to occur creating ammonia gas (NH4- Nitrogen plus hydrogen) which causes Nitrogen to be lost to the air attached to the hydrogen ion of the ammonia. The usual loss is about 25% nitrogen, but adding lime will raise that to about 50% loss of nitrogen.

Extra lime or dolomite may need to be added to your compost pile when the material being composted is quite acid (low pH) such as Fruit waste, due to their naturally occurring Organic acids.

A better method would be to add Calcium in the form of Gypsum (which is naturally occurring) at the rate of 4-6 kg/cubic metre to increase the pH (make it more alkaline) as this will also reduce the odour, especially if you are adding phosphate (say in the form of Superphosphate which is made in a lab)


If your soil is slightly acidic, (low pH, as in Brisbane), then it is better to add the lime or dolomite directly to the soil rather than via the compost material. Whereas the soil in Southern Australia (eg Adelaide) is already alkaline as it comes from limestone so you don’t need to add lime.


Nitrogen is needed to provide food for the composting micro-organisms that oxidise the Carbon in the raw mix. Micro-organisms need about 30 parts by weight of Carbon for each part of Nitrogen used, hence the need for the 30:1 ratio. Soft green garden waste, kitchen scraps and grass clippings are high in Nitrogen, while dry, brown and woody material, eg dry leaves, branches & straw, are low in Nitrogen but high in Carbon.

A compost heap high in Nitrogen but low in Carbon will quickly turn stinky and mushy and so is undesirable. If you have too much Carbon, Urea or Sulphate of Ammonia, can be used to provide extra Nitrogen (N).

If high Nitrogen organics are not available, using two grams of urea (46% Nitrogen) or using 10g of Sulphate of Ammonia (28% Nitrogen) per cubic meter, will increase the Nitrogen.

Carbon and Oxygen

Carbon is there for the microbes to feed on but excess Carbon containing materials such as thick branches, will take a long time to break down (2 to 3 years or more)

The heap requires oxygen to oxidize the carbon. To ensure oxygen reaches all parts of the heap as frequently as possible, it is necessary to turn the entire heap regularly, every 3-4 days. While smaller heaps do not require as frequent turning since oxygen can penetrate them, they do not generate as much heat as larger heaps within the same timeframe.

Greenhouse Gases

A compost heap starved of Oxygen will start to produce Greenhouse gases – another reason to turn your compost heap regularly.

Commercial compost mixes frequently incorporate Ferris sulphate (FeSo4) to introduce iron and impart a dark brown color to the mixture. However, the resulting “compost” appearance can be deceiving, as it may appear fully composted despite being only 3 days old and thus relatively raw and highly undesirable. Ferris (Fe) is the scientific name for iron.

Micro-organisms need a good supply of Phosphorus (P) with a ratio of Carbon to Phosphorus (C/P) of 75-150. Leaves (especially Gum leaves), woody plant residue, and sometimes lawn clippings have a carbon level above 1500, requiring the addition of extra phosphorus. Adding a light sprinkling of 2% phosphorus is sufficient to balance the compost, as excessive amounts can hinder decomposition. Typically, superphosphate is used, but organic alternatives such as bone dust, rock phosphate, or mineral rock dust can also be utilized.

Provided a wide range of organic material is used no other nutrient is needed by the micro-organisms. Be aware organic matter from over-worked soils may have major deficiencies of nutrients and therefore not very useful to the micro organisms in your compost heap.

(C) Oxygen

Aerobic microbes require oxygen, and they are referred to as aerobes. Anaerobic microbes do not require oxygen and are known as anaerobes. Aerobes facilitate faster composting of organic matter in heaps. In cases where anaerobes dominate the composting process, they generate a foul odor containing sulfur. This necessitates the frequent turning of large heaps to ensure oxygen reaches all parts of the heap. However too much oxygen can dry the heap out requiring more water. It is a fine line between wet and dry compost.

(D) Water

The moisture in a compost heap should roughly be 50-55% moisture (ideally 55 g water + 45 g organic matter). Below 40% moisture the composting is slow but over 60% the heap becomes anaerobic. In hot & dry times the heap needs to be moistened. But during a wet season it’s better to cover it so it doesn’t get too wet.

(E) Cations

Particles in the soil called “colloids” attract cations, which are ions with a positive charge. Depending on how many negative charges the colloid holds, will determine how many positive charges the colloid can attract, hold and exchange for other Cations. The more negative charges the colloid holds the greater the Cation Exchange Capacity (CEC) it has. When the colloid has only a few negative charges, it cannot attract and retain a significant amount of positively charged cations. As a result the loose cations are leached away when it rains. Or when you water your garden.

Sand only has a few ‘negative’ charges on its colloids, and therefore cannot attract enough ‘positively’ charged Cations to make it nutritious.

Clay is said to have lots of negative charges on its colloids so can attract plenty of positive charged Cations.

Humus and Organic Soil Matter are even better than clay and therefore have a high Cation Exchange Capacity (CEC). So adding a small amount of compost to your soil can greatly improve its nutrient qualities.

The higher the CEC the greater the capacity of the soil to hold nutrients and exchange nutrients to feed the plants.

As compost matures it increases its capacity to hold and exchange Cations making it more nutritious. However this is also affected by pH as there are acid-forming cations or alkaline-forming cations. Increasing the pH of soil also increases the Cation Exchange Capacity.

Acid forming cations are Hydrogen (H) and Aluminium (Al) Alkaline forming cations are Calcium (Ca), Magnesium (Mg), Potassium (K), and Sodium (Na), and Ammonia (NH4).

(F) pH Effects

Initially a compost heap is slightly acid (about pH 5.5) because plant cell sap is acidic. It then becomes even more acid (lower pH) from the acids made by the bacteria. During the Thermophilic (heating up) stage the heap becomes alkaline (over pH 7) because of ammonia formation. The natural buffering capacity of humus converts ammonia to protein, resulting in it becoming near neutral (pH 7).

Many factors, such as the composition of your compost or the frequency of turning it, can alter the pH. It is just another part of overall compost principles to consider when composting.

(G) Temperature Effects

As microbes feed and multiply, they give off heat thus heating up the heap. A compost heap has a good insulation layer around it so it stays hot. The inside of a large heap often reaches 60°C as they have a smaller surface area to volume ratio so loose heat slower, while small heaps will probably only reach 55°C inside.

Mesophilic micro-organisms

Mesophilic micro-organisms (those that are active below 40°C), become dormant as the heap heats up. The Thermophilic microorganisms (those active above 40°C) replace them. As the temperature drops to below 40°C within the heap, the Mesophilic micro-organisms become active again.

Thermophilic organisms

Thermophilic organisms become inactive at temperatures over 60°C, so the heap tends to be self regulating but because they become inactive the heap takes longer to finish breaking down. All heaps need monitoring and if they are consistently too hot then the heap needs to be reduced in size.

During turning, the internal temperature may drop by 5-10°C but it returns to its initial temperature within a few hours.

The Thermophilic stage kills most pathogens and parasites at 55-60°C, preventing their survival. Achieving this requires up to 3 weeks of composting within the centre of the pile. Therefore, it is crucial to keep infected plants within the inner parts of the heap for at least 3 weeks or, ideally, to exclude them from the heap altogether. Dispose of them in your council bin.

Trouble Shooting

  • a) Smelly compost. Excessive moisture in the compost, either from rain or an abundance of wet food (from kitchen waste) and insufficient dry material, or inadequate air in the mixture, typically causes this issue. Fix it by mixing in some dry material like leaves, OR turn the mix to get more air into it OR raise the mix up (eg spread out on planks) to give better drainage or add calcium in the form of Lime or dolomite. Or the other option is to use cardboard.
  • b) Unwanted visitors. Ants, cockroaches, mice or rats sometimes invade the compost heap Fix it by covering the heap with green organic matter then cover the heap with underfelt, hessian or a polythene sheet. Turn the heap to disrupt the “visitors” OR put fine wire mesh under the heap to stop mice & rats but which still lets in the earthworms. Avoid adding dairy products, meat or seafood to the mix.
  • c) Compost is too slow. Maybe the heap is not hot enough OR does not have enough air OR not enough water Fix it by adding Nitrogen rich material such as lawn clippings or kitchen scraps. Turn the heap more OR add some water. Cover the heap in winter so it does not get too cold


It can be quite an art maintaining and managing a compost heap. There are many other various options to composting that work in various different ways. A Compost heap is just one method. The trick is working out what option works best for you and your needs.


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