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Composting Fact Sheet
11/11/1999
What is composting?
Composting is simply the method of breaking down waste organic materials (kitchen and garden waste) in a large container or heap. The decomposition occurs because of the action of naturally occurring bacteria and fungi. Small invertebrates, such as earthworms and millipedes, help to complete the process. Composting can convert kitchen and garden waste into dark coloured soil in a matter of a few weeks or months.
Composting has many benefits for the environment. It
- saves valuable tipping space
- can be used as fertiliser
- improves the condition of soils.
How composting works
There is nothing mysterious or complicated about composting. Natural composting, or decomposition, occurs all the time in the natural world. Organic material, the remains of dead animals and plants, is broken down and consumed by decomposers (mainly bacteria and fungi) and eaten by small invertebrates.
The nutrients, that were once present in these remains, are returned to the soil or water, where they are able to support the growth of new plants. This is natural recycling.
In composting, provided the right conditions are present, the natural process of decay is speeded up. In these conditions, bacteria and fungi feed and multiply, giving off a great deal of heat. In well managed heaps, this temperature can reach as high as 60 degrees Celsius in the central core.
While the temperature remains high, invertebrates are not present in compost heaps, but when the temperature drops, the invertebrates enter the heap from the surrounding soil and complete the process of decomposition.
In a pile of mature compost, there may be a wide variety of invertebrates present. In fact there is a mini food web in action. Some creatures, such as springtails, millipedes, mites, slugs and earthworms, feed on the partially broken down materials. Other creatures, such as spiders, centipedes and scorpions, prey on the plant feeders.
Choosing a composting system
When choosing a composting system for your home, it is important to understand the types of decomposition that can occur in a compost heap or bin.
Forms of decomposition
Anaerobic
Anaerobic means that decomposition occurs without oxygen. This process is quite slow and can give off unpleasant odours and, more importantly, methane, which is a powerful greenhouse gas.
Aerobic decomposition
In aerobic decomposition, the breakdown is caused by the action of micro-organisms that thrive in oxygen. This process is quite rapid and can cause the heap to become quite hot. Aerobic decomposition does not usually produce unpleasant odours.
Many references on composting refer to aerobic and anaerobic systems. This distinction is misleading, as under certain conditions, so-called “anaerobic systems” (usually closed plastic bins) can operate aerobically and so-called “aerobic systems”, if managed badly, can give off unpleasant odours, indicating that they are operating anaerobically.
Whichever system you finally choose for your home, it is important that you operate it aerobically, so that it does not produce methane and other unpleasant odours. To do this you should:
- add roughly equal amounts of “greens” (kitchen waste and fresh garden waste) and “browns” (fallen leaves and shredded paper);
- keep the heap moist, but not too wet;
- place the bin on well drained soil to improve drainage; and
- turn it frequently to aerate the organic material (if this is not possible, then insert a piece of plastic agricultural pipe, with slits in the side, into the centre of the heap. This will help to bring air into the centre of the heap.) With closed plastic bins, you can drill small holes in the sides to improve aeration. Cover the holes with fly wire to prevent flies from entering the bins.
What to add to a compost heap
Vegetable and fruit scraps
Fallen leaves (in layers)
Tea leaves and tea bags
Coffee grounds
Vacuum cleaner dust
Soft stems
Dead flowers
Used vegetable cooking oil
Egg shells
Old Newspapers
Grass cuttings in layers
Sawdust (not from treated timber eg. treated pine)
Wood ash
What NOT to add to a compost heap
Meat and dairy products
Diseased plants
Metals, plastic, glass
Animal manures (especially the droppings of cats and dogs)
Fat
Magazines
Large branches
Weeds that have seeds or underground stems
Bread or cake (may attract mice)
Bones
Sawdust from treated timber (eg. treated pine)
Adding compost worms to compost bins will also help to aerate the organic material and reduce anaerobic breakdown.
Tumbler type compost systems will, if operated correctly, involve rapid aerobic breakdown and produce compost in a very short period of time.
Compost containers and heaps
There are many types of containers that you can use to compost at home. Some of these are:
- Plastic bins with ventilation holes or slits
- Plastic bins without ventilation
- Metal drums with holes punched in the side and with the base removed
- Rotating drum units (tumblers)
- Enclosures made from timber (planks or sleepers), bricks, or chicken wire.
If you prefer, you can make compost in open heaps, but they should be covered with either a plastic sheet or some hessian to prevent the heap from drying out in hot weather. You could even bury kitchen scraps in holes in garden beds.
Precautions
Composted material is produced from natural materials and contains a variety of living organisms which, on rare occasions, have been associated with illness and allergies in humans. For health reasons, it is very important to take the following precautions when handling compost or soil:
- Wash your hands after handling compost or soil materials.
- Protect broken skin by wearing gloves.
- Avoid confined spaces for handling compost or soil materials.
- Keep compost moist to prevent the spores or bacteria in compost from becoming airborne.
- Gently wet dry compost to allow dust-free handling.
- Avoid direct inhalation of dry compost.
For individuals who have either allergies to the fungal spores in compost or depressed immune systems, it may be necessary to wear a face mask when working with compost. Severely affected individuals may have to avoid contact with compost altogether. Elderly gardeners should be especially careful when working with compost materials.
Sources
EcoRecycle Victoria web site & Good Compost Guide (Modified excerpts from Waste Matters by P. Armstrong and J. Laffin have been used).
Other composting Information Sheets.
Refer to Information Sheet 12 Methods of Composting and Information Sheet 13 Troubleshooting with Compost and Mulching.
Useful References
Armstrong, P, and Laffin, J., 1993, Waste Matters - Environmental Education Activities about Waste, Gould League.
Clayton, S., 1993, The Reverse Garbage Garden, Hyland House, South Melbourne.
Cullen, M. and Johnson, L., 1992, Backyard and Balcony Composting, Bookman Press, Melbourne.
Cundall, P., 1993, Organic Gardening, Gardening Australia Collector's series No. 1, Federal Publishing Company, Alexandria NSW.
Gilbert, A., 1992, No Garbage, Thomas C. Lothian Pty Ltd.
Nunes, K, 1998, The Good Compost Guide: A Directory of Compost Bins and Wormeries, Gould League and EcoRecycle Victoria.
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