One of the most important elements in landscaping in compositing, if your soil is unhealthy you have little chance of producing healthy plants. Composting is a way of speeding up the natural process of plant decay. It is excellent gardening practice because it not only returns nutrients to the soil but it also reduces waste. The process has been used by farmers for at least 4000 years but has only recently been "rediscovered" by city gardeners as they have become more concerned about the environment.
The composting process
Soil scientists have been studying the composting process since the 1930's and have removed much of the guesswork. A good compost is made up of organic materials (plant wastes), microbes, moisture and oxygen. The microbes which digest the plant matter need the oxygen and water to live and thrive. The oxygen comes from the air and so a loose "aerated" compost heap will benefit the microbes and help them do their work efficiently. A damp heap will ensure that the plant matter is easily decomposed by the microbes. If it is too dry, the plant material becomes hard for the microbes to break down. If it is too wet, anaerobic bacteria will take over, making the heap smelly and not hot enough to kill off plant pests and diseases.
How to make a good compost
There are two methods of making compost and which method you favour will depend on how quickly you want the compost process to happen and how much effort you are prepared to exert. A third alternative is to purchase one of the various types of compost bins now available through retail outlets.
The Berkley method was devised by the University of California and is labour intensive. However, a fine compost can be produced within one month.
The Indore method was devised by a British soil scientist who studied the age-old techniques used by farmers in the Indian state of Indore. It requires little effort but does take up to a year to produce usable compost.
Rotary compost bins are designed to work by the Berkley method whereas static square or round bins work on the Indore method. Choose according to space available, effort required and budget.
Worm bins are useful for recycling kitchen vegetable scraps where outdoor space is restricted. They are ideal for townhouses and units.
The Berkley composting method
Build a mound of about one cubic metre using grass clippings, leaves and other clean garden or vegetable matter mixed with a little soil and perhaps some garden fertiliser. The materials can either be added in layers or mixed together prior to mounding. Wet dry materials before adding them to the heap. Add water as necessary to maintain an evenly damp heap.
After three or four days, turn the heap to mix and aerate the materials. Repeat this every two or three days until the compost is suitable for your requirements. This should be between two and four weeks after setting up the heap.
The Indore composting method
This type of compost heap works best with a base of about 2 metres square and a height of about 1.5 metres. Build the heap on a base of loose material such as brush or tree branches to allow good aeration. Using alternate layers of low nitrogen and high nitrogen material build up the heap and then encase the heap with a 5 cm layer of compacted soil to keep out flies and prevent the escape of odours. Leave a depression on the top of the pile to catch rainwater.
Best location for composting
Keep the heap or bin out of the midday sun so that it does not dry out and away from roots which will tend to grow up into the compost. You are more likely to be diligent with kitchen wastes if the heap is within easy reach of the house. A well-managed compost heap will not produce bad smells so odour should not be a consideration in locating your heap.
What organic matter you can process
Any organic matter can be processed in a compost heap but some combinations work better than others. A good mix is 50% weeds, 20% leaves and 30% grass clippings. Paper, sawdust and straw are low in Nitrogen and will need a supplement of nitrogen-rich materials such as manure or urea.
Turning the compost
Turning a heap helps the process of decomposition. The outer materials should be moved to the hotter interior of the heap to kill off pathogens and the whole heap should be fluffed up to improve air flow. The effort of turning is what will bring your heap closer to the Berkley model.
There are three main reasons for the failure of compost heaps.
1. The material is too wet. You can tell this by the foul odour produced by anaerobic decomposition. Add more dry material and turn the heap
2. The material is too dry. You can check if it is too dry by digging into the heap. If it is, sprinkle with water while turning the heap.
3. The carbon/nitrogen ratio is too high. You can tell this is the problem if the decomposition process slows down or stops after initially working and there is no foul smell and the heap is not dry. Add high Nitrogen materials such as lawn clippings, dog droppings, urine or a nitrogen fertiliser such as urea.