A good compost is made up of organic materials, microbes, moisture and oxygen. Microbes will benefit from a loose, aerated compost heap, and a damp heap ensures that the plant matter is easily decomposed by the microbes. If a compost heap is too dry, the microbes struggle to break down, and the result is a smelly heap, not hot enough to kill plant pests and diseases.
Making a good compost
There are two methods of making compost, and your choice of which one to use depends on how quickly you want the compost process to happen.
The Berkley method is labour intensive, however a fine compost can be produced in one month. To use this method, build a mound of about one cubic metre, using grass, clippings, leaves and other clean garden or vegetable matter. Mix this with garden fertilizer and a little soil. If materials are dry, wet them before adding them to the heap; continue to add water when necessary in order to maintain an evenly damp heap. After three or four days, turn and aerate the heap. Repeat this every few days.
The Indore method requires little effort but takes up to a year to produce usable compost. This type of compost heap works best with a base of about 2 square metres, and a height of about 1.5 metres. Build up the base using loose material such as tree branches which allow for aeration. Use alternating levels of low nitrogen and high nitrogen material to build up the heap before encasing it in a layer (about 5cm) of compacted soil. This will keep out flies and prevent odours escaping. Leaving a small depression on the top of the pile will enable the catching of rainwater.
The location of a compost heap
Avoid placing the heap or bin somewhere that will catch midday sun. Odours escaping should not be an issue, if your compost heap is well-maintained.
What to process
All organic matter can be processed but some combinations work better: 50% weeds, 20% leaves, 30% grass clippings. As paper, sawdust and straw are low in nitrogen, manure, or another nitrogen-rich material will need to be added.
Turning helps with decomposition. Drier, outer materials need to be moved to the hotter interior to kill off pathogens. The whole heap should be ‘fluffed up’ to improve airflow.
Reason for the failure of compost heaps
- The material is too wet. To remedy this, add more dry material and turn.
- The material is too dry. Establish if this is the case by digging into the heap. To remedy, sprinkle with water and turn.
- The carbon : nitrogen ratio is too high. If the decomposition process slows down after working effectively initially, this may be the problem. To remedy, add materials high in nitrogen such as lawn clippings, dog poo, urine or a nitrogen fertilizer like urea.