Hot composting has a few benefits over cold composting. It requires a little more attention and labour than cold composting, and is more suited to those with large volumes of organic matter in batches, rather than continuously adding to the heap. It is the fastest method of composting, and the best way to deal with large amounts of garden waste such as pruning off cuts and leaf litter.
The high temperatures reached in a hot compost heap allow beneficial micro-organisms to thrive and accelerate the breakdown of the compost, and if maintained at the right temperatures should kill any weeds, seeds or pests within the heap. Depending on the size of the heap and the materials used a hot compost heap will produce finished compost within a few months or even a few weeks if well maintained.
Hot composting is also excellent as it doesn’t require a container or compost bin, and is most often built as a free standing heap. It can be covered with a tarp or plastic to keep away pests and provide insulation to keep your compost at the ideal temperatures. If you do not have the space for a large heap hot composting can also be done in an enclosure similar to that used for cold composting. A tumbler or barrel design is excellent as it makes the process of turning your compost very simple, compost bays are suitable if you have the space, or any kind of plastic compost bin can be used to contain the compost heap.
How to make your own Hot Compost heap
You should aim to build the heap roughly 1.5m wide and roughly the same height, this is the minimum size needed to reach the high temperatures required in the centre of the heap. You will need enough garden waste to build a pile this size.
You can almost any organic matter into a hot compost heap, basically anything that was once living. Finely chopped or shredded material is best as it has a greater surface area and creates more air pockets, meaning it breaks down very quickly and helps to produce the heat required in the compost pile. The most important factor in creating a healthy compost heap is balance, the most important elements are air, water, and a good balance of “brown” and “green” ingredients, equal parts of each is a good ratio to begin with.
Begin your heap by creating a layer of “brown” ingredients, and continue to build alternating between “green” and “brown” layers, each layer should be roughly 150cm deep. As you add each layer you should also add enough water to moisten the materials. Aim for a sponge-like texture rather than completely soaking the ingredients. You can also add a sprinkle of blood and bone or any organic fertiliser as a compost starter, or use a small amount of finished compost to begin the next batch.
Keep layering ingredients until your pile is roughly 1.5m high. It is a good idea to cover the compost heap with plastic or a cover of some kind to help maintain the temperature and protect the heap from heavy rains and dry spells. The compost heap is now ready to go, and should begin to generate heat within a few hours. The heap will reach temperatures of up to 80oC at the centre as bacteria and fungi break down organic matter and produce heat.
Maintaining your hot compost heap
You will need to turn your heap regularly, about once a week is ideal. This will help to keep your compost balanced and regulate temperature. As the centre of the heap reaches high temperatures it is possible for the heap to become too hot, or become too anaerobic and stagnant. This is easily avoided with regular maintenance to keep your compost balanced. Monitoring temperature is important, turning the heap is also very important as it introduces more oxygen to the heap.
You can check the temperature by sticking a metal rod of any kind into the centre of the heap, hold it there for a minute or two, and then check the temperature by feel, this will give you a rough idea of how warm your heap is. If you’d like to be more precise there are compost thermometers available at most garden centres, or you can even try attaching a meat thermometer to a pole for a DIY compost thermometer.
You can remove the finished compost when the compost has broken down to a rich dark soil-like consistency and no particles or pieces remain. This will take between 1-6 months, usually somewhere in between, and a well made compost heap can begin to produce finished compost within a few weeks. Your homemade compost is now ready for you to use, and makes an excellent soil conditioner and mulch.
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