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. alternating
layers of high-carbon (brown materials, such as dead leaves) and high-nitrogen material (green materials, such as grass clippings) or mix the two together and then heap into a pile. If alternating layers, it is suggested that each layer 5 to 10 cm
is made thick. Althought there are many other layering combinations and we show a number on this site. Layering is a simple way of getting the desired ratio of greens and brown
Some composters find that
mixing the two together in advance is more effective than layering and the National Trust, at some sites, use a machine to grind and mince the green and brown waste using a ratio of 40% of greens and 60%
Use approximately equal amounts of each. If you are low on high-nitrogen material, you can add a small amount of commercial fertilizer containing nitrogen. Apply at a rate 125 ml of fertilizer for
each 25 cm layer of material. Adding a few shovels of soil will also help get the pile off to a good start; soil adds commonly found decomposing organisms.
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 for two or three days but can last for to three or four weeks or several months depending on ther size of the heap. During this stage the temperature rises from 45-65 °C. It can rise to 75 °C but should be controlled so that
it does not exceed 65°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
The 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 metres in size but can be much bigger depending on
the size of the garden or grounds providing 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. The
area should be well-drained and level. The bins can be made out of old pallets, planks,decking or in the case of large bins railway sleepers or cement blocks. The soils within the bin can be covered with a 6-8" layer of twigs, sticks or stalks to assist
in creating airflow through the contents. A layer of woodchip can also be used as an alternative base material this makes emptying the bin easier than shovelling sticks.
However, that is the minumum recommended size. Larger
bins will retain the heat much more effectively and, depending on the size of the garden the bins in large gardens are often about 5cu feet on size as above this size it is more difficult for air to circulate within the bin. But bins of seven or eight
cublic feet are often used. Bins larger than this be difficult to turn by hand and a tractor or other mechanical means will be required.
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.
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
The heap should be covered 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.
The 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.
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.,
I recommend 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