Principles of Backyard Composting
Composting is a controlled process which speeds up the decomposition of organic wastes into a soil like material. Heat and carbon dioxide are also produced in the process. Composting can take place under either aerobic (with air) or anaerobic (without air) conditions. Aerobic composting is faster and is the preferred method for backyard composting. The composting process uses microorganisms such as bacteria and fungi to break down the organic materials. Like all living organisms, the microorganisms need a continuous supply of food, water and air.
Food
It is important to give the microorganisms a "balanced diet". Although most organic materials provide all the nutrients for the microorganisms to grow, they grow best with certain levels of carbon ( C - otherwise known as "browns" ) and nitrogen ( N - otherwise known as "greens" ). Paper, leaves and wood are high in carbon while grass clippings and vegetable scraps are high in nitrogen. Combining the correct "mix" of carbon and nitrogen materials in the composting "recipe" helps to get the best results. A mixture of materials with more browns (higher carbon content) takes longer to break down, and a mixture with more greens (higher nitrogen content) creates odours. It's important to mix different materials to achieve a proper balance of browns (carbon) and greens (nitrogen).
Most materials have both carbon or nitrogen in them but some of them are more brown than green. For instance, grass clippings have a carbon nitrogen ration of 19:1, while dried leaves have a ration of 60:1. Grass clippings (unless they have been dried) are considered a "green" while dried leaves are considered a "brown".
Most backyard composters are not going to sit down and calculate the C:N ratio of the materials they are putting in their compost pile. Therefore, it is perhaps more useful to think about the amounts of material you need to add. A good rule of thumb is to add equal amounts by weight. For instance if you add 100 g of dried leaves you would add 100 g of green grass clippings or vegetable wastes from you kitchen. The actual mix you put in will depend on the materials you are adding.
If you have too much brown material in your pile, it will take a long time to break down and it won't heat up as fast. If you add too much green material, it will smell. In order to find the right mix it is important to observe what is happening in your pile so that you will know if something needs to be changed.
Composting Materials
Food - Apples and peels, Artichoke leaves, Asparagus bottoms, Berries, Bananas and peels, Beans, Beet tops, Broccoli stalks, Brussel sprouts, Buckwheat hulls, Cabbage stalks and outer leaves, Carrot tops, Carrot scrapings, Celery tops, Citrus rinds, Coffee grounds, Corn cobs (chopped), Cucumber, Egg shells (crushed), Grapes, Grapefruit, Lettuce, Lemon, Melon, Oats, Onions, Pears, Pineapple, Potato, Pumpkin, Squash, Tea, Tomatoes, Turnip, Zucchini
Other - Algae, Apple pomace (cider press waste), Bird cage cleaning, Blood meal, Bone meal, Corn stalks, Cotton rags, Feathers, Felt waste, Flowers, Garden wastes, Grape plant waste, Granite dust, Grass, Hair, Hay, Hops, Leather waste & dust, Leaf mold, Leaves ,Manure, Muck, Peanut hulls, Peat Moss, Pine needles, Rope, Sawdust, Seaweed, Soil, Straw, String, Weeds, Wood, Ash, Wool, Rags
Materials NOT Recommended in Backyard Composting
Meat, bones, fish scraps - attracts dogs, cats, insects & rodents - takes a long time to break down
Oil, fatty material, dairy products - oils and greases take a long time to break down - affect the breakdown of other materials - attracts insects
Pet litter - may contain disease organisms harmful to humans
Diseased Plants - the heat of a home compost pile may not kill the diseased organisms or any insects or eggs infecting a plant.
Dishwater - most dishwashing soaps contain perfumes and greases
Barbeque Ashes/coals - highly resistant to decomposition - contains excessive amounts of sulphur
Surface Area
Materials should be broken into small pieces and well mixed to evenly distribute the organic materials and create air voids. If materials are left too large, they will take an extremely long time to decompose.