Composting is a great way to reduce your household waste by up to one third, while producing a rich soil conditioner for your garden, lawn and houseplants. For those who have never tried to compost, or are just beginning, odour is a common concern. A hot and healthy compost pile will not create offensive odours. To prevent odours from developing, here are a few simple things to remember.

1. Do not add large, unchopped items to the pile.
   Compostable items that are about 2.5 centimetre (1 inch) or smaller in size will break down very quickly as they offer more surface area for the decomposer organisms to work on.

2. Make sure each layer of material is no more than 10 to 15 cm (4 to 6 inches) thick.
   A compost pile consists of layers of browns (carbon sources), such as finished compost, soil or dried leaves, and greens (nitrogen sources), such as food waste, fresh yard waste etc... These materials must be alternated and added in equal layers.

3. A little soil goes a long way...
   When adding food waste to the pile, bury it in the centre and cover with a 2.5-cm (1-in) layer of finished compost, soil or dried leaves. This prevents odours and adds helpful microbes to the pile.

4. Water is important, but ...
   The proper amount of moisture in the pile is very important in the control of odour. Too much moisture can create a rotten egg smell. Keep the whole pile as damp as a well-wrung sponge.

5. NEVER add meat, bones, dairy products, fats or oils to your compost pile.
   These materials will smell as they decompose and may also attract unwanted insect and animal pests.

6. Make sure there is a lot of air in the pile.
   A compost pile that does not have enough air is called anaerobic (without air). To prevent an anaerobic compost pile, poke holes through it with a broom or rake handle, a stick or a commercial aerating tool, or turn it with a garden fork.
   
   You can also create an airstack that will regularly allow air into your pile. Place a bundle of sticks, about 15 cm (6 in) in diameter (tied with rope), or a piece of plastic pipe punctured with small air holes, in the centre of your compost pile.

   

Common Odours

Ammonia
An ammonia smell means that too much nitrogen-rich material has been added to the pile. Materials that are high in nitrogen content include kitchen food waste and green grass clippings. These are called green materials and they must be balanced with carbon-rich or brown materials to properly decompose in a compost pile. Materials high in carbon include brown leaves, dried grass clippings, dried garden plants and straw.

Always add equal volumes of green and brown materials. Turn and mix the materials in the compost pile; dampen to the wetness of a well-wrung sponge; and top with a 2.5-cm (1-in) layer of soil. The soil will trap any remaining ammonia and turn it back into nitrogen.

Rotten Egg
Compost piles that are too wet, or too compacted, will become anaerobic and give off a rotten egg smell. To solve this problem, turn the pile with a garden fork or shovel to allow more air into the pile. Mix in dry leaves or a similar dry material to absorb moisture. Repeat this step for a few days. Then place a 2.5-cm (1-in) layer of soil on top of the pile to introduce more decomposer organisms to the pile and reduce the odour.