Aerobic composting is a faster and easier method, that gives good results, based on maintaining high oxygen levels (airflow) in the heap. When oxygen levels are higher; decomposition is potentially faster.
The heap should be approx. 1 cubic metre.
It may be enclosed by a circle of open wire mesh, or built as a dome shaped mound, as follows:
- Carbon – woodier materials, such as prunings, sawdust, or autumn leaves
- Nitrogen – use leafy materials such as grass clippings, fruit and vegetable peelings, and soft prunings. Do not include diseased plants or weeds.
These above two groups should be approximately of equal quantity.
- Protein – Animal manures, such as cow, sheep, poultry, pig and horse manure, and/or blood and bone.
- Moisture – The moisture level should be between 40 and 60%. You can test this by taking a handful of the composting material from a depth of 15 –20 cm into the heap/mound of compost material, and squeezing it. It should be about as moist as a sponge that has been wet, and then moderately squeezed dry.
- Oxygen – This is incorporated by regularly aerating and turning the heap.
- pH – The pH will change during the stages of maturity. Generally you need not do anything to alter the pH.
Place the ingredients in thin layers (e.g. 10 cm). Moisten each layer. Do not tap it down as you are building the heap. The heap needs to be very light and fluffy. Alternate between high Nitrogen and h igh Carbon containing materials where possible.
In 24 hours white filaments can often be seen - this is an indication that the micro-organisms are doing their job. The heap should be producing a lot of heat, which is also an indication that the micro-organisms are hard at work. If there are not white filaments forming then the heap could be too dry, in which case build it again and moisten between the layers. The amount of water added depends on the level of moisture already in the grass and leaves.
Turn the heap once a week for 3 – 4 weeks, bringing the outside parts to the middle and if it looks dry and is not quickly decomposing, moisten between the layers again. A pipe with holes drilled in the side can be placed vertically through the centre of the heap to increase the supply of oxygen and hasten the decomposition. If the heap is too wet and smells, mix in more dry, dead leaves or dry grass. You can also improve drainage under the heap by placing a layer of twigs at the bottom.
Composting in Bays
Use star pickets and rot resistant timber to construct a 4.5 metre long, 1.5 metre deep open-air bay that is divided into three areas.
When first bay is full turn the material into the second bay and start filling the first again.
When the first bay is full again, turn the contents of the second bay into the third, the first into the second and start to fill the first again.
Composting time with this method, in a mild, temperate climate is generally between 2 and 3 months.