Composting is a method of speeding up the decomposition of organic materials. The ingredients are made into a heap of at least 1 cubic metre. Heat given off by microorganisms inside the heap is trapped there by the insulation provided by the outer few centimetres. Inside temperature rises and so does the rate of decomposition. Composting is most rapid when the heap is made with the ‘right’ ingredients and turned frequently.

Principles

• A compost heap can be thought of as an enormous number of microorganisms having a fantastic time consuming a mountain of food. If they are provided with the right conditions they will do the rest. ‘Right’ conditions are:
• plenty of organic matter for energy;
• enough nutrient elements, especially nitrogen;
• oxygen - those microorganisms that are best at decomposing plant materials need plenty of oxygen;
• moisture - not too much, not too little;
• a source of cations, especially calcium, to stabilise the compost;
• sometimes, adjusted pH.

Decomposer microorganisms

Some hundreds of species of microorganisms, mostly bacteria, fungi and actinomycetes (branching bacteria), are involved in decomposing organic materials. They and their spores are everywhere - in the air, on this page, on living plants. They remain inactive until conditions for their growth and reproduction are favourable. As a plant begins to age and die, they invade it, beginning the process of decomposition.