This method needs to be seen and felt to be believed.
Hot composting is a phenomenon of nature whereby under favourable conditions thermophilic microorganisms thrive in your compost heap and break it down in record time, producing amazing amounts of heat in the process.
Since I cracked hot composting a number of years ago it has become a cornerstone activity at the Ansa Permaculture Design test site. Subsequently I have employed it for many of my client projects.
What are the conditions for good hot composting?
- Air: It is an aerobic process – the micro-organisms need air to breathe.
- Water: They need moisture. You must totally soak the pile at the beginning.
- Heat: Thermophilic bacteria & friends like a temperature of between 55 – 65deg C hence:
- Large compost pile size: A larger pile has a higher volume: surface area ratio and so also has a higher heat generation to heat loss ratio also. A starting pile of 1.5m cubed or greater is recommended
- Carbon to nitrogen balance: the materials used in composting should have a chemical balance of about between 25:1 or 30: 1 Carbon to Nitrogen. All organic matter will have more carbon than nitrogen anyway so in practice this means making a heap with a mix of (relatively) high nitrogen “greens” and high carbon “browns”. Examples of “greens” are grass mowings, vegetable peels, animal maure and urine. Examples of “browns” are shredded paper, wood chip and straw. Shredded hedge clipping comprising of leaves and twigs make a very good “ready mix” of the right proportions.
- High material surface area: Use well chopped up material to give the micro-organisms plenty surface area to act on.
Hot Compost Method
This is my variation of the Californian “Berkely Method”. To honour its origins I’ve collaborated with well known Californian rapper “Baby Bash” in making the backing track for this tutorial – enjoy!
- Build a tall flat topped pile of about 1.5m3 in size
- Build the pile in alternating layers of “greens” and browns of about 5cm thickness. Start with a layer of “browns” to admit air under the pile
- Soak each layer with water as you build the pile. You could have a well directed spray hose on all the time for this purpose.
- Cover the pile with a tarpaulin and leave for 4 days – the pile gets hot.
- Every 2 days thereafter turn the pile with a pitchfork. This involves moving the pile by progressively skimming off the material at the top and sides of the pile to make the centre of the new heap. At the end of the move the material at the centre of the old heap becomes the outside of the new one. This way all of the material gets time at the centre of the heap and so gets properly composted. It also admits fresh air to the heap and prevents temperatures getting too hot for the bacteria.
Remember: Chop and Soak!
In practice the ratio of high carbon “brown” material to high nitrogen “green” material is quite forgiving. The key steps that are easy to forget however are to chop up the material as much as you can first, and to really soak the heap at the start before you cover it for the first time. It will also work if you can’t turn it exactly every 2 days. I’ve found every 3 days can work as well, especially for the later stages. Using this interval however will draw the process out to about a month long altogether.