Greens and Browns layered in a bin before turning.
Alternating in this way helps give the right ratio of Greens & Browns
Most people use a cold, or passive composting system when they first start composting as it is simpler and requires less effort as material from the kitchen and garden is added to
the bin as and when it becomes available. The disadvantage of this technique is that it is slow (taking 6 –18 months) and does not kill seeds or pathogens.
Hot composting involves more work than cold composting but
will produce compost in a much shorter time (25- 90 days) it kills seeds, perennial weeds and pathogens. I personally feel that is more rewarding as the efforts of the composter contribute to the quality of the finished product.
The four phases in the hot composting process are:
The first mesophilic phase during which the temperature rises to 40-42 °C. This stage may last for only a few
hours or a couple of days depending on the bin and contents;
- a thermophilic phase lasting from a few days up to three or four weeks where the temperature rises from 45-70 °C.
- a second mesophilic
phase occurs as the material cools allowing mesophilic organisms to recolonize the bin and
- the final phase is that of maturation (or curing) which can last for several weeks to several months.
objective in managing the temperature of the material is to prolong the thermophilic stage so that the heat kills pathogens and seeds but without the temperature rising above 65/70 C when beneficial microorganisms will be
killed. A good visual warning that the bin is to hot is provided by the growth of a white “mould”, actually anaerobic thermophilic bacteria. Which means that the appears of the white growth acts as a warning to cool the bin. This “mould”
will disappear when the temperature drops
While a “cold composting system may benefit from a sunny location the hot composting area should, if possible, located so that it does not get dried out too
much sun or waterlogged heavy rain.
Hot composting bins need to be at least one cubic meter in size but can be much bigger depending on the size of the garden or grounds from which the feedstock. When hot compost
it will be necessary to have easy access to the bin to turn the material so a one cubic metre bin will require at least 1.5 x 1.5 metres of space.
Most Hot composting systems involve adding the organic
material in a “Batch” to fill or half fill the bin at the same time. Normally a bank of 3 or 4 bins are used so that the material can be aerated by turning from one bin to the next. If the material is to be turned by hand a bin of about
1m x 1m x 1 or 1.5m high is preferred. If mechanical turning is to be used the bin can be considerably larger.
In the basic hot composting system, the bin is filled with equal parts of Green and Brown materials. These
need to be cut, chopped or shredded into small pieces ideally 1- 2”. Decomposition takes place on the surface of organic material if it is chopped, smashed, -or cutt into small particles, (less than 2-inches in diameter), more
surface area is created and decomposition happens faster. Depending on the technique manure, mature compost or soil may be added as a source of additional microorganisms or lime may be added to control acidity. Layers of addition Greens such
as comfrey or nettles may be used as an activator. Water should be added as the pile is built, often between each layer. To breakdown quickly a moisture content of 50% will be required
At this stage you could cover
the heap both to maintain moisture, and to prevent the material becoming waterlog during wet weather.
When starting to use a new bin or a significant change of feedstock the temperature should be monitored
regularly taking the pile temperature every day or every other day if possible, for a period of about a month. The temperature should rise to 40 -76 C in the first one or five days. The actual temperature will vary
with the bin size, moisture levels and microbial activity.
The contents of the bin should be aerated by turning whenever the temperature falls below 40C which is normally about every four of seven days.
Some composters turn the bin routinely every couple of days or weekly while others record the temperature and turn the contents when the temperature falls. After a slight delay the temperature will rise again.
recommended turning technique is to turn the material round the edges of the bin to make the central core of the new bin and while what was the hotter central core to form the new exterior of the new pile ( see diagram). This
ensures that the cooler edges of the bin during the first week is heated in the hotter central core during the second week.
The moisture level of the contents should be adjusted each week during the turning stage,with water
being added to maintain the correct moisture levels being careful that it does not become waterlogged as this will both cool the contents and may result in the formation of undesirable anaerobic patches.,
the monitoring, recording temperatures and turning is continued for a month by which time the temperature will fallen to below 30C (depending on ambient temperatures) and most of the material will have turned into dark, crumbly compost
The compost should be left to mature for at least two weeks before use as a mulch