Health and Environmental Services Information Sheet 15

Composting

Home composting has been used for many years by keen gardeners and is now being encouraged by the Town of Bassendean as a means of reducing the amount of waste being discarded to landfill. About one half of your rubbish is compostable kitchen and garden waste. This page is intended to provide information on how to compost in a safe and environmentally beneficial manner using a compost bin.

What is Compost?

Compost is partially decomposed organic matter. The process of decomposition is almost entirely due to bacterial action and is a complex series of steps whereby certain strains of bacteria and fungi breakdown the material to a point where other strains take over until material reaches a manure-like state.

Composting is a method of speeding up and controlling the natural breakdown of organic matter in a soil-like substance for use as garden mulch and fertiliser.

Good compost is a complete fertiliser for all vegetable and plants and is comparable with farm manure. It provides both basic food and valuable soil conditioner called 'humus'.

Most of your kitchen wastes can be turned into compost which makes composting a cheap method of converting your wastes into material for use in the garden soil.

How to Get Started

Your compost bin has an open bottom. It should be sited in a warm sunny area and in direct contact with loose soil to allow drainage, air-flow and entry of earthworms and micro-organisms.

Earthworms contribute to efficient composting, but only after the hot period as the heat will kill them.

What to Use

Grass clippings, kitchen waste, paper wrappings, fruit and vegetable peelings, leaves, prunings (shredded), tea leaves and bags, indoor plants, coffee grounds, egg shells, manure, weeds, vacuum cleaner dust, hair and wool, cardboard, paper and sawdust.

What Not to Use

Animal products (meat, fat, whole bones), plastic, large branches, waxy plant material, diseased plants, plant seeds, underground stems, pesticide-contaminated plants, disposable nappies.

Using the Compost

Correctly prepared compost has a pleasant earthy smell, has few recognisable pieces of the original organic material and is a fairly uniform dark brown or black colour. It may be used as soon as the temperature has dropped below 40 degrees Celsius.

The finished product can be either dug into garden beds for vegetables or flowers, spread as a mulch around shrubs and trees (keep 40-50cm away from the trunks of trees) or sieved and used as a top dressing for lawns.

Ensure compost is not too dry and dusty when it is spread. The dust from dry compost may cause allergy or respiratory symptoms and should be avoided.

Full Bin

Many people choose to have two compost bins so that one can be left to finish composting while the other is being filled.

When using only one compost bin, wait until it is full. Lift the compost bin off the heap and place in a new position. Shovel the top material that has not yet fully composted back into the bin.

Earthworm Composting

Feeding earthworms in a wooden or plastic bin is another good way to make high quality compost from food scraps and there is no need for turning because the earthworms will automatically aerate the material for you. It is an especially good idea for people who live in units or flats who only have a small courtyard or balcony.

The container should have a lid and holes to let the worms breathe and be about 90cm x 60cm x 45cm high for the average sized family.

Put pre-soaked bedding material such as animal manure and shredded paper to a depth of about 15-20cm.

Feed the worms anything organic (except citrus peel and onion) placed on top of or buried slightly in the bedding and replace as the worms consume it.

You will not only produce great compost for your pot plants, but breed more worms which can be put in the garden.

What are the benefits?

Use of compost on your garden will:

save water. The water retention capacity of the soil is increased; and
save on fertilisers and soil improvers. Compost helps retain artificial fertilisers in the soil so that they can be taken up by plants. Nutrients from compost release slowly throughout the growing season and are less easily lost by leaching than nutrients in soluble fertilisers. There is an increased ability for the soil to absorb rapid changes in acidity and alkalinity and to neutralise organic toxins produced by some plants.

Recipe for Success

All organic material is largely made up of different proportions of carbon and nitrogen. For composting to work, the correct ratio of carbon to nitrogen is required. The ratio is about 25-30 parts by weight of carbon to each part of nitrogen.

A rule of thumb is to mix 4 parts of soft nitrogenous material such as grass clippings, weeds, fruit and vegetable peelings and wastes with one part of sawdust, shredded prunings, newspaper and dry leaves.

To help speed decomposition, chop or shred all your kitchen and garden waste. Place in layers about 20cm thick and include some nutrient-rich material such as finished compost, sheep or cow manure or blood and bone. The herb Yarrow is also a good compost starter. Garden soil can also be used to supply the bacteria that do the composting. It is better to use a mixture of materials rather than have heavy layers of just leaves or grass clippings.

Composting microbes are already present but the process can be sped up by adding some mature compost.

Care and operation of your compost bin

The compost requires aeration. Materials put in normally (not compacted) will usually have sufficient air. Additional aeration can come from stirring or creating a vertical vent in the material in the bin by driving a sharp stick slightly from side-to-side to widen the vent before removing the stick. Aeration is necessary to provide oxygen and evaporate any excess moisture since water is formed during composting.

The compost should be damp, not soggy or wet with the moisture content of a lightly squeezed sponge, so it may be necessary to add a little water, especially in the summer. Too much water will reduce the air flow and cause foul odours.

Aeration and correct water content are necessary to ensure that the compost will reach temperatures necessary to destroy pathogens, parasites and weed seeds.

Care should be taken to ensure that:

there is sufficient air flow to prevent odours;
the material is well mixed;
temperatures reach between 45 and 55 degrees Celsius, at which disease causing bacteria, parasites and weed seeds are normally destroyed. This is why it is best to locate the compost bin in a sunny spot. In the winter months, when ambient temperatures are lower, temperatures in the compost will also be lower and compost should be cured for longer periods (up to four more weeks) in order to destroy pathogens.
the right amount of moisture is present (about 50%) to promote aerobic decomposition and to reduce the risk of respiratory complaints from inhalation of spore-containing dust.

What are the Health Risks?

A properly cared for and operated compost bin or tumbler poses little threat to health. However, open compost heaps (which are illegal in WA) and poorly operated compost systems may cause health problems by encouraging breeding of flies and other pests and the odour is a problem.

Unless adequate temperatures are reached within the compost, the composting process does not eliminate disease causing microbes and it can also encourage the growth of fungi and bacteria which occasionally cause respiratory complaints.

Problem	Cause	Solution
Nasty Odours	Compost too wet.	Leave lid off in dry weather.
	Too much grass cuttings.	Remove some cuttings. Leave cuttings on lawn for a few hours to dry out before adding to bin.
	Compost too acid.	Mix in several handfuls of garden lime.
Slow decay	Not enough heat being generated.	Position bin in sunlight.
	Lack of air.	Increase aeration. Move bin and reload contents.
	Too dry.	Moisten compost.
Vermin	Meats and fats.	Remove unsuitable materials.
	Easy access	Place bin on sheet of galvanised 12mm mesh.

This information is provided courtesy of the Environmental Protection Authority, the Compost Bin Manufacturers, the Department of Health and the Town of Bassendean.

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