When grass clippings, apple peels and other organic materials get tossed in with the rest of the household garbage, the potential for harvesting the goodness of these natural materials is lost forever. Instead of being used to create free fertilizer, these items become part of a toxic brew of chemicals and heavy metals at landfills. Home composting is a simple way to reduce the burden on landfills while greatly benefiting garden plants.

Science plays a role in creating good compost (a rich humus). Adequate moisture, air, carbon-rich and nitrogen-rich materials are essential. When these elements are available in the right proportions, they aid in decomposition, encourage the growth of aerobic bacteria and attract worms and other small organisms. Without these elements, the compost pile may sit for months without decomposing and may begin to smell rather unpleasant.

The materials inside a compost bin should be moist but not soaking wet. Vegetation typically contains enough liquid to maintain proper moisture inside a bin. However, in hot, dry weather you may need to pour a few litres of water on the pile every week or so. Adequate airflow is usually achieved with openings up the side of the bin. Plastic containers specially designed for composting are available from many municipal governments and from gardening supply stores. It is also possible to build a functional bin with a wood frame and chicken wire although manufactured bins usually offer the advantage of a sliding door at the bottom to retrieve finished compost.

Carbon-rich (brown) materials include dry leaves, straw, sawdust, and dried grass clippings. Nitrogen-rich (green) materials include fruit and vegetable scraps, plant trimmings, fresh grass clippings, coffee grounds and tea leaves. Bacteria, worms and other beneficial organisms need a balance of carbon and nitrogen along with various other nutrients such as natural sugars.

What to compost

1. Fruit and vegetable trimmings
2. Coffee grounds
3. Cornstalks and cobs
4. Eggshells - It helps to crush them first.
5. Horse and cow manure
6. Garden trimmings - You can run a mower over larger leaves to speed decomposition.
7. Sawdust
8. Wood ashes - Small amounts add carbon to the compost bin but large amounts can slow the composting process.

What not to compost

1. Barbeque ashes/coal - These contain sulphur oxides and other chemicals.
2. Fish skin - It attracts animals.
3. Cooked food - This attracts animals and can slow the composting process.
4. Kitty litter - It may contain disease organisms.
5. Dandelion seed heads - Do not try to compost mature seed heads as this resilient plant will soon begin to sprout out of the sides of the bin.

Adding to the Compost Bin

The way you add materials to your bin will affect how well and how thoroughly they become compost. Choose a bin that has a volume of approximately one cubic metre. This size is large enough to retain heat and moisture in the centre of the bin. At the bottom, add a layer of coarse material such as branch cuttings, leaves, or straw to aid in air circulation. Next, add some nitrogen-rich grass clipping or fresh leaves. Add kitchen scraps to the centre of bin and cover with a thin layer of soil (approximately 3cm). This will deter flying insects that are attracted to fruit. Whenever possible try to alternate layers of fresh green materials with brown materials remembering to keep kitchen scraps in the centre.

Once you have your bin about halfway full, things should begin to heat up! As micro-organisms such as bacteria and fungi consume (decompose) the materials inside the bin, they create heat. This heat helps to kill some harmful bacteria and weed seeds. Proper composting involves temperatures between 43 °C and 65 °C (110 °F and 150 °F). The process of decomposition is complete when the temperature of the pile declines and remains below approximately 40 °C (105 °F). Allow the compost to mature for another two to six months to ensure that it will not produce any unpleasant odours. If you have a large amount of material, you may wish to have two bins-one for new material and another for maturing compost.

Compost bins are wonderful ways to make lawn trimmings disappear! As materials decompose inside the bin, they typically shrink in volume as bacteria and fungi consume the nutrients and some of the water content. To help speed up the process, you may wish to chop up large scraps. Smaller pieces offer more exposed surface for micro-organisms to invade.

You can harvest your compost at the bottom of the bin. The large, plastic models available at gardening stores typically have a sliding door at the bottom to allow you to remove finished compost. If your bin does not have a door, you may need to tip over the unit and collect the completed compost. This is a good opportunity to mix materials that are still in the process of decomposing.

After months of 'feeding' and aging, your compost will be ready to use on your garden. There are several ways to make use of this nutrient-rich humus. You can shovel some around the base of trees and shrubs. You can mix it into the topsoil around flowers and vegetables. You can even make tea out of it. Put a litre of compost into a piece of cloth and tie it up. Then soak the bag overnight in a garbage can full of water. Serve the 'tea' to plants only-they will appreciate the potent, healthy brew.

Whichever method you choose, your plants and our landfills are sure to appreciate your efforts!