Composting

Contents

Composting is a natural process where micro-organisms, insects and earthworms decompose organic matter such as food scraps and garden waste into a soil-like material. Compost is a rich source of nutrients for your garden. Composting also helps to reduce the amount of rubbish you throw away, which saves you money and helps our environment by reducing the amount of waste going into our landfills.

Ingredients for composting

For a healthy compost mixture you need a good balance of these four ingredients:

GREENS + BROWNS + AIR + WATER = COMPOST

GREENS
(high nitrogen content)
BROWNS
(high carbon content)
Vegetable scrapsTree clippings (only small twigs & branches)
Fruit scrapsDried leaves
Coffee grounds and filtersStraw and untreated sawdust
Tea leaves and bagsShredded paper towels, paper serviettes & tissues
Lawn clippingsShredded paper or cardboard
Plant clippingsEgg shells
FlowersBreads, grains and pasta

Paper products and cardboard should be ripped into small pieces prior to composting and soaked in water for the best results.

Twigs and small branches should not be thicker than your finger and should be broken into small pieces for the best results.

What not to compost

These materials should not be placed in your compost bin:

  • Bones
  • Cooking oils or fats
  • Dairy products
  • Dog or cat waste
  • Glass, metals or plastics
  • Hazardous substances
  • Liquids
  • Meat, fish or poultry
  • Plant residue with chemical spray
  • Styrofoam
  • Weeds
  • Wood or timber

Step by step guide to making compost

Step 1Choose your site. Compost bins or heaps should be located in a sheltered, level area of your garden that has good drainage and access. Don't make it difficult for yourself by putting the bin in a hard to reach place.
The site should ideally be within reach of a garden hose and preferably not in full sun. The compost heap should sit directly on the soil or a grass area.
Step 2Before positioning the bin, turn over the soil with a garden fork or spade on the site to add drainage and encourage earthworms into the heap.
Step 3To ensure good drainage and aeration, try to start the heap with a 10‑15 cm layer of coarse material such as tree clippings or mature compost (desirable but not essential).
Step 4Add a bucketful of greens (eg fruit, vegetables, lawn clippings) and a bucketful of browns (eg leaves, twigs, paper). Add water if the mixture is dry as the compost needs to be moist. The heap should heat up and shrink after a few days.
Step 5Continue to add green and brown material to the heap. The best compost is made from a 50/50 split of green and brown material. When the bin is full, close the lid and leave the compost to mature.
Step 6For optimal results, turn the heap every few weeks to increase air circulation and expose fresh material to insects and other organisms. Add water if the heap becomes dry.

​Getting the best from your compost

​Odours

A properly built compost heap will have a small amount of odour but it should not be unpleasant. Strong and unpleasant odours usually result from an unbalanced compost heap, eg composting grass clippings on their own, adding too many food scraps or adding the wrong types of foods. Bad odours will also occur if the heap becomes too wet or has too little air. To keep odours down, turn your compost heap each time you add material to enhance aeration and make sure you don't over-water your heap.

Animals and Pests

Adding food to a compost heap can make it more attractive to pests. In urban areas, the best way to avoid pests is to use an enclosed compost bin like those offered at home and garden stores.

Climate

The decomposition process that breaks down your food scraps and garden waste into compost is faster in the warm summer months than in the winter. Make sure you cover your compost to keep out the rain.

Kitchen bin

It is a good idea to have a small kitchen scrap bin to store food scraps as they are produced. When this bin is full, you can transfer the food scraps to your compost bin outside. To keep odours down it is preferable to have a bin with a lid and to line your kitchen scrap bin with newspaper. The newspaper can be thrown into the compost bin after each empty. Make sure you only place acceptable food scraps in your kitchen scrap bin.

Mature compost

It takes a while for compost to mature. Turning the compost will speed up the process and it should take around three to four months if the compost is regularly turned. If the compost is not turned, it should take up to nine months to a year for the compost to mature. Make sure to check the moisture content of the compost and add water to the heap if the material is dry. The compost should have a moisture level similar to a squeezed-out sponge. Ideally the finished product should look like potting mix but your compost does not have to be perfect. As long as most of the material is broken down (egg shells will not completely disappear) and you have material with a soil-like structure, your compost is ready to add to your garden.

Using the compost in your garden

You can use your compost at any time of the year. Early spring is a good time to add compost to your garden to help boost soil fertility, soil moisture retention and plant growth. The compost should be mixed into the top 5cm-10cm of your garden soil. If your compost is quite coarse you might want to pick out some of the branches to make it finer.

Page reviewed: 26 Jun 2014 12:52pm