CompostSoil Biology

Different Degrees of Compost

Before and during shots of a compost pile built for demonstration during a
PDC.So this is 14 days into the process, not 60 days at completion.

Many words these days have become so broad in their use that they have lost real meaning. The word ‘love’ is a perfect example. In one breath people express love for a dog, pizza and their partner. The word compost has suffered a similar fate. What many call compost is more accurately defined as “an accumulation of rotten/rotting organic material” or “a stinky breeding place for flies”. I love compost so I want to rectify this rotten situation.

Well intentioned gardeners across the world accumulate yard waste, house scraps and maybe even some manure from a hamster or the house hens in the back corner of the yard. The piles are continually added to, so the process of decomposition is never really completed. This means the offensive odors and unappealing textures repel gardeners from ever moving the ‘composted’ material to the growing beds where it is needed. On the other hand, possums, rats, raccoons and flies love these buffet spreads and the pile acts as a magnet for every worm in your yard, concentrating all their benefits directly below the ‘compost’ pile where nothing grows.

When it comes time to use this material on the garden, you sow for yourself hours worth of weeding because the pile has never reached a high enough temperature to denature the weed seeds. But don’t worry, with a better understanding of the composting process you can compost those weeds properly next time you dig them out of your growing beds.

So what is real compost?

Compost should be a diverse pile of measured ingredients in which moisture, oxygen and temperature are managed to create ideal breeding habitat for a beneficial suite of micro-organisms. This diverse community of beneficial microscopic life aids the breakdown of organic material and creates humus. That’s brown gold soil humus, not Mediterranean restaurant hummus.

While there is much that science does not know about the creation and real composition of humus, there is consensus on its many benefits. It is commonly believed however, that humus is made up, at least in part, of the bodies of microbes that have played their role in decomposition of organic material. So the more microbes you can breed during the life of the compost pile, the more humus you should end up with.

It should always be kept in mind that the aim of composting is to breed micro-organisms and the end product of the process should be the creation of humus. For those paying attention there lies in these simple statements a real challenge. To measure success in breeding cattle is simple because the specimens are large and the populations comparatively small. To breed microorganisms is challenging because the specimens are microscopic, as the name suggests, and the populations are, for all practical purposes, innumerable.

There is however one main indicator that will, once you are armed with some knowledge of these microbes , allow you to monitor their populations and activity. That indicator is temperature.

There are two broad categories which these armies who decompose the raw materials of your compost pile can be divided into. These are mesophilic and thermophilic. The mesophilic kind are microbes that thrive in temperatures of 10°C – 45°C and thermophilic thrive between 45°C – 70°C. Trials show that most seed in a compost pile is denatured when compost is held at 55°C for 3 days. So you want the thermophilic microbial life in your pile. Many pathogens are also killed at this temperature. For this reason, milk is pasteurized at 72°C for a duration of 15 seconds. It is recommended that all parts of the compost stack achieve at least 55°C for a minimum of three days. In order to ensure that all materials achieve that temperature, move the outer materials into the core of the stack when turning.

A sturdy handle like this is advisable so that the dial face does not get damaged
when pushing and pulling the probe in and out of your compost pile.

Measuring the temperature in a large stack (ideally at least 1m³) can be challenging without the correct tool. If you need to dig into the pile to insert a small, conventional thermometer you lose heat as you open the pile, so your reading is not accurate. The same is true if you need to dig to insert the probe of an electronic device that is on a flexible wire instead of a rigid probe that can penetrate an undisturbed pile to any depth you choose. If we are at all serious about gardening we need to be serious about compost production. Someone who is an aspiring compost producer will often get frustrated and give up if they are not armed with the right tools. Those tools are simple: a good ergonomic compost fork for turning the pile and an accurate and durable temperature probe.

Fiskars make a great, purpose built, light and ergonomic compost fork.

When you compare the cost of a quality compost probe like the ones available through PRI’s online store, to the cost of bags of fertilizer, synthetic or organic, it is clear which is the better investment. The purchasing of fertilizers is a repetitious investment while a good temperature probe is a one-time buy for a lifetime of efficient, effective and rewarding composting. My experience has been that until I invested in one of these temperature probes designed specifically for composting, my composting was a hit and miss endeavor, and we all know that success breeds success. Every successful gardener need to be a compost master. Every successful compost master needs the right tools.

Once you have the ingredients in your heap in the correct ratios (approximately 45% high carbon material, 35% green material and 20% high Nitrogen material), the other key factor, along with monitoring the temperature, is the moisture. Your hand is a sufficiently accurate gauge for this. Take a handful of material from about 300 mm into the stack, squeeze tightly and it should produce a single drop of water. If it does, the moisture content of the stack is most likely adequate. At the very least you want to have a wet palm after squeezing it. If the stack is too dry to wet your hand, the stack needs to be turned and watered using a fine mist whilst turning. For more detailed instructions and explanations you can find resources here and here.

Below is a suggested guide for the turning temperature in your pile and the accompanying turning schedule. If the pile is turned in a way that maintains the correct temperature and moisture in the pile, you can be confident your oxygen levels are appropriate also.

  • Day 1 temperature: 20°C, similar to air temperature
  • Day 2 temperature: 10°C increase in temperature to 30°C-40°C
  • Day 3 temperature: Optimally you have achieved 50°C-65°C in the core of the stack
  • Day 3-10 temperature: Maintained between 50°C-65°C (with proper moisture levels maintained)
  • Day 11 temperature, 1st turn: Turn the stack and temperature may drop to 40°C, moisten with fine spray if needed whilst turning and mixing the stack.
  • Day 12 temperature: Returned to 50°C-65°C and maintained until 2nd turn at day 20.
  • Day 20 temperature, 2nd turn: Turn the stack and it should be turned every 10 days to maintain moisture and for aeration, once stack is turned, temperatures should be in the 40s°C.
  • Day 22-24 temperature: Similar to day 12. May be slighter cooler, temperatures in the 50s and maintain temperatures in the 50°C-60°C range for 10 days until the
    next turn.
  • Day 30 temperature, 3rd turn: Materials should show signs of decomposition
  • Day 30-35: Temperatures return to the 50s°C and maintain temperatures in the 50s for an additional 10 days with good moisture management.
  • Day 40 temperature, 4th turn: Temperatures drop when turned, and increase to 45°C-55°C over the next 5 days. There should be significant signs of decomposition.
  • Day 40-45 temperature: Temperatures in the high 40s – 50°C and maintained for the next 10 days until turned on day 50.
  • Day 50 temperature, 5th turn: Temperatures dropping with increased signs of decomposition. Stack may now be about half its original size. (Note: you might reduce the diameter of the wire cage to increase height of the stack or combine two stacks into a single stack if making multiple stacks).
  • Day 50-55 temperatures: Dropping to 30°C to 40°C with extensive decomposition once temperatures are 10°C above air temperatures, compost is ready to be used.


  1. Good article Samuel! I’ve been on a mission to inform people of the difference between compost and what’s usually in the ubiquitous black bins too.

    I’d add that a volume of 1.5 cubic meters is a good minimum, since it has sufficient volume after settling to keep temperatures high.

    Also that turning is not really necessary unless the temperature is over 65 degrees or you need to incorporate new material. The more you turn it the more you will disturb fungi growing in it. We often need to get more fungi out into our soils as they are typically bacterial dominated. Balanced or fungal dominated soil is beneficial depending on what we are trying to grow. I’ve found that after a while the heap will soak up water by sprinkling from above.

    Another great tip is that the white fungal looking material that can soon appear is a filamentous actinobacteria called streptomyces. It thrives in low oxygen conditions, so indicates that the material is going anaerobic. It creates antibiotics that are detrimental to fungus; bad news for any of the 90% of plants that are mycorrhizal. Bad smells and black colouring are also tell tale signs. Finished compost should be chocolate brown, crumbly and smell neutral or earthy.

    Dr. Elaine Ingham’s material (of Soil Foodweb International) has been invaluable to me in understanding compost, worm compost, compost tea, soil, nutrition and disease – but there is still much to learn.

  2. Thanks for the article Sam.

    I tried the Berkley compost and I didn’t succeed to have a finish product in 18 days. Composting is definitely an art that need practice. My pile was way too small to create a decent environment for microorganisms. Next time I’ll try with a wire around.

    Now here is my question, for everyone to get their head around.

    Why do you personally choose to do a hot compost pile and not a cold compost pile? What are the advantage/disadvantage?

    I am trying to get my head around the best way of doing my compost (in Switzerland, cold-temperate climate). I spent 6 months working with the Grow Biointensive method where we do cold compost pile with a C:N of 60:1. The aim being to create the more possible stable carbon for a long term approach of storing carbon into the soil and really building the carbon structure. But it feels like the microbes are a lot less active than with a hot compost. My understanding is that with a cold compost pile we create more compost per unit of compost material due to not having the loss through the microbial activity (the heat).

    If someone had any deep research about the subject I would be very grateful.

  3. I can see the benefit of rapidly producing weed-free compost thermophilically, though I do enjoy the ‘ubiquitous black bin’ approach too. 3 or 4 of these bins gives you a low effort compost supply. Dump it in, collect next year (in cold climate). It’s not the rolls-royce approach but it still gives a useful product, with much less effort (but still enough effort!). I need persuading to go to all the effort of preparing ideal compost ingredients, turning, watering… since they say a cold process results in much the same end-product, just over a longer timeframe (?). I don’t mind too much about weeds because I also mulch. Very happy to be persuaded, though!…

  4. Hoi Oscar
    are you living in Swiitzerland too? I’m from Wädenswil and research in composting too.
    How can we get in contact?

  5. I live in an area of Western Australia where we ownly seem to get compostable material for about 4 months of the year in winter the rest of the year my land is a dust bowl with dam all rain . I water a postage stamp area of lawn but due to the heat it does not grow much so other than food scraps which the chooks have first go at and the rest goes into my compost bin as cold compost that eventually breacks down over twelve months and is used in the vegie patch the following year I do not buy in compost as the local suppliers cannot guarantee the quality of their product as wholly organic so its a bit of a problem to get compost so my garden effert strugles a bit but what I do get to grow is o so tasty compared to shop bought foods that I keep on trying. good luck composting to all those who have compostable matter to use .

  6. Sorry, but why wait so long? Geoff (In Permaculture Soil) shows the audience how-to compost in 18 days. With the correct c:n ratio and moisture you should be golden.

    30:1 c/n

  7. Tom – there can be a big difference in the product of a well managed compost pile and a pile of organic matter left to itself. If it goes anaerobic (which is very common) different organisms take over. A lot of nutritional value is lost via gaseous anaerobic waste products (e.g. ammonia, hydrogen sulphide, phosphene) and produce liquids wastes that are harmful to roots (e.g. alcohols, organic acids). It tends to have poor structure, and doesn’t kill weed seeds or pathogens. Disease causing organisms thrive in these conditions. The yeast can attract flies (including fruit fly and other pests). Vermin can be attracted to exposed food scraps and dry piles good for nesting.

    Tad – The Berkeley method is OK if you have the time & energy, and you want a bacterial dominated compost. Turning disturbs the fungi and fungi tend to grow slowly on complex foods. I’m not yet convinced that the compost is actually ready to use at day 18. When I tried it the middle of the pile was still at 48 degrees and I didn’t build the heap as large as I should have.

  8. Hi Stephen,

    I am in New Zealand at the moment but I come back to Switzerland next friday. I will be at the “Festival de la Terre” in Lausanne the Sunday 16th june

    We can keep this discussion on private, here is my email: [email protected]

  9. Roger Mitchell, I understand your predicament. While in Yemen the year before last I was helping people to build compost piles. It was a real mission to find green material. Nitrogen will not be your issue because you can accumulate the chicken manure. Green material, you will need to design that source into your system. Observe your environment for the plants that are pioneering. Will grow well with out much care and maintenance other than chopping them back to harvest for you compost pile construction. This can be trees, shrubs or ground covers. Observe or research what accomplishes this function for you, get an area established for that purpose and then time the building of your compost piles for the peaks in green matter on these plants. If water is scarce maybe this green matter garden can be planted near grey water outlets.
    As your productive garden grows in size the green matter available to you will snow ball.

  10. Oscar,
    I dont have deep research but my thought would be to do both. Depending on your requirements. I have not had experience with cold compost but have wondered why Kay does it that way. Sounds like soil carbon is the goal for them and I understand they had issues with that in the past so that may be a priority for them to get balance back in the system. The aim of this thermophilic pile is to breed biology and create humus as a result. In the same way Tim is suggesting a different method if fungal domination is your goal. ‘Horses for courses’ as we say in English mate.
    I have Dr. Ellaine Inghams book on my near future reading list and I think you would enjoy the influence of this book on your learning journey. As you saw at PRI compost teas are a way to enhance the biology further and get more returns on the energy invested in any compost pile. Berkley, cold, or longer term thermophilic. But that is something for another blog : )

    Tim Auld. Thanks for you contribution to this conversation. I found it very valuable.

  11. A thought for Roger. With regard to your local compost supplier not being able to guarantee the organic status of their compost.
    I would not be overly concerned about what has gone in to their ingredients, as long as it has broken down with thermophilic action.
    Most things we would be thinking of as contaminants will be dealt with by the microbial action and made inert.
    My understanding with things like organic certification is that you can use any natural inputs regardless of their organic status as long as they are composted thermophilically.
    I would be asking what the ingredients are, if its mostly chipped green waste and some form of animal manure I would feel very confident that it is fine.
    I would have a few more reservations if it was human waste from a council facility as there could be a lot of heavy metals, but these would be stable as long as your pH was close to neutral.

  12. Hi to every one, Im in the tropics Panama to be more specific, Im completely new on composting subject, any book or tips recommended to this kind of climate, we basicaly have 4 months dry and 8 month really wet.
    We have enough green material, access to coconut (sponge…I dont know the right name in inglish but I guess you know what I mean) I thought of this product as it keeps moisture really well and theres air in between the fibers, no wood chip access, for carbon I thought of maybe dry grass and small branches (no wood chip machine). The locals use here ashes but I dont really understand the beneficials of this.
    Basically we have access to what nature provides here, but no end up products as shown on one of the videos.
    I also used a kind of compost tea (guess I could call it like that) just collecting leaves from Gliricidia sepium and had great results against fungi on my citrus plants, and as a fertilizer.

    looking forward to your comments!

  13. Would it be an area of interest to inhibit heavy-metal uptake by garden plants? I did an experiment. I made some Nano Particle Iron Phosphate and added it to my soils to competitively inhibit those very noxious things like Cadmium in my Kale and Broccoli. I believe that riding our food chain by heavy metals should reduce many diseases like breast and prostate cancer. Mother nature has abundant challenges for us. Heavy metals are natural as a baby’s smile. Use science to rid of them.

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