|Visible layers of organic waste in a compost heap cross-section|
|Typical Nutrient Content|
|Average homemade compost|
Compost is a combination of decayed or decaying organic matter, this process produces a dark crumbly soil which is rich in plant nutrients and has many uses. It is a simple process and as a result is often done domestically as well as commercially.
First prepare a site to store your compost. Ideally it should provide at least four walls, and no floor so that worms can access the materials inside and assist with the process. Combine compostable ingredients in your chosen receptacle and cover to retain heat. The heat in the pile aids the decomposition process and is particularly essential to speed up the degradation of brown materials.
Shredding ingredients before adding them to the compost heap can aid in their combination and speed up the process, as can regularly mixing it.
Brown matierals (such as dry grass, dead leaves etc) contain higher concentration of carbon than green materials (such as fresh grass clippings or vegetable waste), these green materials contain more nitrogen than brown. For ideal composting a compost pile should contain 30 parts carbon and 1 part nitrogen, for example, fresh grass clippings have a carbon:nitrogen ratio of 15:1, whereas leaves contain 50:1. Mixing green grass and brown leaves in equal parts should achieve approximately the right combination.
Most green plant material contains around 40% carbon, brown plant materials generally comtain 50-60% carbon, however the nitrogen level varies widely.
An ideal compost needs the right combination of carbon and nitrogen as well as air and water. It is therefore necessary to ensure the materials you combine in the compost heap allow some circulation of air without allowing it to become too dry and that it contains moisture without becoming saturated. Adding dry materials such as newspaper or sawdust will help both aerate the heap and absorb water, adding fresh organic materials, urine or water will help combat excessive dryness.
Compost can include any of the following ingredients, green items are fresh or will compost quickly, brown items are dead or will take a long time to decompose.
Uncooked kitchen waste
- Vegetable Peelings (17-25:1)
- Tops and tails of vegetables - carrots, onions etc. (17-25:1)
- Fruit peel & cores (25-40:1)
- Sweet corn cob stalks - Shred first. (60:1)
- Egg shells - crush fully first
- Tea bags - these combine faster if they are torn open before adding
- Coffee grounds - are high in nitrogen, but are also acidic (20-25:1)
- Urine - this can be applied directly to most plants. It is sterile, has a high nitrogen content, contains many minerals beneficial to plants and acts as an activator to the decomposition process. (1-2:1)
- Wood ash - ensure that the wood has not been treated and there are no nails/screws in the ash. (25:1)
- Newspaper - this helps to provide essential air pockets in the compost as well as absorbing excess water. (175:1)
- Cardboard - Shred first and use sparingly as it will dry the pile out and takes a long time to decompose. (350:1)
- Egg boxes - it is advisable to tear these into small pieces to speed up their decomposition
- Household dust - emptying your vacuum cleaner bag into the compost will help to absorb excess water, but be sure what it contains
- Natural fibres - e.g. wool, cotton
- Hair/nail clippings
- Nut shells (35:1)
- Cigarette/cigar ash
- Soft prunings (30:1)
- Nettles - are high in nitrogen. They can also be used on their own as a nettle tea
- Grass cuttings (20-25:1 fresh)
- Weeds - avoid pernicious weeds and those which have gone to seed (20-30:1)
- Seaweed (19:1)
- Bracken - this is a very good source of potassium if your plants commonly suffer from potassium deficiency.
- Leaves - due to their high carbon:nitrogen ratio; leaves take a long time to break down. It is advisable to compost these separately to produce leaf mould. (50-80:1)
- Hard prunings - such as twigs and woody chips. Ideal this should be shredded first. Use very sparingly (300-700:1)
- Pine needles - these are very acidic and waxy, they break down very slowly, use very sparingly. (80:1)
- Used peat pots - shred before adding
- Sawdust/wood chips - ensure the wood has not been treated. Use sparingly. (300-700:1)
- Humus (soil) - use sparingly in the pile. It can be used as a 1-2 inch layer ontop to 'seal' the pile. (10:1)
- Chicken manure - this will act as an activator and cause the compost to decompose quicker. (7:1)
- Manure from all other herbivores (Cows, horses, chickens, turkeys etc) (20:1 rotted)
- Animal bedding from herbivorous pets (rabbits, guinea pigs etc) such as hay, straw, shredded paper, wood shavings. (hay: 90:1), (wood shavings: 300-700:1)
(Approximate C:N ratio)
Do not include any of the following materials in ordinary compost:
- Cooked food
(The above materials are likely to attract rats)
- Coal & coke ash
- Disposable nappies
- Potato seedlings - these may survive the composting process and re-seed when used in the ground
- Potato & Tomato cuttings which show signs of blight - It can be advisable to avoid these entirely just in case
- Pernicious weeds - such as morning glory/bindweed, sheep sorrel, ivy and several kinds of grasses. These are likely to resprout from their roots
- Cat & dog waste - dog waste can contain large roundworm, called Toxocara canis, which can also infect humans. 90% of puppies may be infected with these. The principle disease in cat faeces is called Toxoplasmosis which is present in around 45% of cats and can cause malformation and abortion in pregnant women
- Human waste - proper composting of human faeces requires the pile to reach thermophilic temperatures (45-80°C) for a sustained period to destroy any disease organisms. The potential health risks of not achieving this make human faeces an inadvisable compost addition
- Gotaas (1956), Composting, p. 35