Turning your rubbish into fertilizer
Every year, Australians throw away thousands of tonnes of household waste. Next time you take out your wheelie bin, look at what you are throwing away!
Almost half of our domestic rubbish consists of kitchen and garden waste. Most of this material can be composted. Composting reduces the amount of rubbish we throw away, decreases our need for landfill sites and provides a chemical-free fertilizer for our gardens.
Composting is a cheap and hygienic method of converting your kitchen and garden waste into a clean-smelling material used in the garden as a soil conditioner. Properly controlled, it should end up as a dark, crumbly fertilizer with a pleasant, earthy smell.
Compost not only returns nutrients to the soil that would otherwise be lost, but also improves soil structure and increases the water holding capacity of the soil.
Composting is not new. Compost has been used in crop production for over 4000 years. Artificial fertilizers only became widely available a century ago. Australia, an old, eroded continent, is suffering from land degradation. Composting is one of the keys to soil care in rural and urban situations.
How do I compost?
Compost can be made in either a heap or bin, depending on the amount of material for composting and the needs and size of your garden.
A heap is useful for gardeners with large quantities of waste. Minimum dimensions should be one cubic metre, sufficient to ensure a hot temperature. The heap may be enclosed using bricks or timber. Leave an access area or work space at the front of the heap for turning the compost and cover it with a lid or piece of carpet to retain heat and provide protection from rain.
A compost bin is often better for smaller, suburban gardens. Plastic bins, metal tumblers and plastic tumblers can be purchased from nurseries, hardware stores and local councils. Compost tumblers are available for gardeners who prefer to make compost in bins and want quick results.
Bins should be open at the top and bottom. The top needs a tight-fitting lid. The other end is placed in contact with the soil to allow earthworms to enter. These little gardeners speed the decaying process by loosening the compost and allowing air to enter and circulate. Avoid placing the bin or heap too close to houses. Consider placing it directly on level soil in a garden bed.
Two bins or heaps allow material to accumulate in one while composting in the other. The heap should be protected from hot sun and heavy rain to prevent excess drying or moisture, which prevent effective composting.
Compost works best if you add a balanced mixture of rapidly decomposing ‘green’ material (e.g. fruit and vegetable scraps) and ‘brown’ material, which decomposes slowly (e.g. twigs). These can be added in any order.
Once you have a mixture of materials, cover with a layer of soil, add some water and a lid to keep the heat in and speed the rotting process.
Composting matter should feel damp, but if waterlogged it will smell, attract flies and be inefficient. Control the moisture level by adding absorbent materials such as sawdust, newspaper, straw or dry manure.
Turning the heap with a fork will speed decomposition. The more frequently the material is turned, the faster it will decompose. Care should be taken to make sure that all material is turned into the inner, hottest part of the heap where weed seeds and pathogens are destroyed. If the heap is turned regularly, the compost should be ready for use in a month or two. Your compost can sometimes be smelly when you turn it, so set up your compost away from your neighbours! The heap may be left unturned, but the process could take an extra six to twelve months.
Compost is ready to use when it has a crumbly appearance, an earthy smell and identifying what things were is difficult!
Water – Keep the compost just damp. Overwatering will ruin your compost.
Balance – Add a mix of green and brown materials to make a well balanced compost.
Air – Turn the pile over every few weeks or every 4-6 days if using a bin.
Size – A compost heap will mature quickest if it is at least one cubic metre.
Micro-organisms – Soil animals help break down the compost material. They come from the soil or old compost you add and from the earth on which the compost heap is built.
What should I put in my compost?
Most organic materials which decompose readily are suitable for use in a compost heap. For best results, chop or grind coarse material to speed breakdown.
- Garden wastes – Grass cuttings, non-woody garden prunings, leaves, flowers and vegetable remains.
- Kitchen wastes – Vegetable peelings, leaves and stalks, fruit peelings and cores, cooked table scraps, tea leaves, coffee grounds, egg shells and stale bread.
- Animal manure – Horse, chicken or cow manure (but avoid other animal droppings).
- Paper and cardboard – Include small amounts of shredded newspaper and paper tissues.
- Wood fire ash
- Sawdust and wood shavings
- Vacuum dust and hair
What should I leave out of my compost?
- Woody garden clippings – Branches, roots (unless chipped), rose cuttings and other garden wastes with thorns or nettles, conifer prunings or pine needles.
- Treated wood products
- Weeds with bulbs such as nut grass and oxalis
- Diseased plant material – Put these in the rubbish bin
- Septic tank sludge or toilet waste
- Meat scraps (which can attract rats and mice) and diseased animal carcasses
- Animal droppings – Cat and dog droppings can spread disease
- Any wastes that do not decompose – Metals, glass and plastics.
- Materials that kill the composting bacteria – Fat, oil, salt, disinfectants, antibiotics, herbicides, pesticides, waste recently sprayed with pesticides.
How does composting work?
When making compost, the aim should be to provide air, some moisture and suitable food in the right proportions to keep micro-organisms busy.
When suitable material is collected in a loose heap, naturally occurring micro-organisms such as bacteria, fungi and algae start to feed on the softer, more succulent ingredients. At this stage, the heap can heat up to 60