Hot and cold composting: what’s the difference?

Home composting is an eco-friendly way to turn kitchen and garden waste into a valuable resource which can be used in your garden. Homemade compost is teeming with beneficial microorganisms and nutrients that enhance soil health and help garden plants thrive. There are many ways to make compost, and in this post we look at the key differences between ‘cold’ composting and thermophilic or ‘hot’ composting.

Cold composting is a common method for composting kitchen and garden waste. Waste can be added gradually to a compost bin or a heap. The contents is turned (i.e. mixed up) using a garden fork or compost aerator every few weeks and decomposes over a period of 6-12 months.

Hot composting is a much faster process, and you can get finished compost in up to 18 days. All the ingredients are added at once and as a result, there is much faster growth of bacteria and fungi decomposing the organic matter in the pile. This makes the pile hot – the centre can get as hot as 70 degrees Celsius! The pile must be turned regularly to introduce air, prevent it from getting too hot (this will kill the beneficial microorganisms) and to mix up the materials so that everything breaks down at a similar rate.

If maintained properly, the pile will get hot enough to destroy weed seeds, pathogens and insect pests. This means you can compost materials that you would want to avoid putting into a cold compost pile, such meat, fish, dairy, cooked foods and weeds that are diseased or have gone to seed.

With cold composting, carbon and nitrogen are lost to the air, which means that the finished product will only be 20% of the original volume, whereas with hot composting, the volume stays the same.

Hot composting takes a bit more care and attention, but for those who are willing to invest a bit more time, hot composting can produce excellent results in a short space of time. See here for how to make compost in 18 days using the Berkeley hot composting method and here for how to use a ‘hotbin‘ (takes 30-90 days). For an introduction to additional composting methods, including wormeries and bokashi, and how to start and maintain a composting system, see our guide.

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