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.