In many gardens up and down the land there is a mound of rubbish. Commonly known as the 'compost heap'‚ this consists of garden waste, some kitchen waste and probably grass clippings. Yet if asked about the purpose of the mound, what is done to it, what it is eventually used for, gardeners often give only a vague response. The heap is there - well, because it is there. It serves no particular purpose other than being a dumping ground for plant material designated as rubbish.

Ask any organic gardener, however, about the compost heap, and the response is quite different. This pile of 'rubbish' is managed and nurtured, and the final product is used to feed and improve the soil. A healthy soil is essential to produce vigorous, disease resistant plants - in an organic garden, compost is the key to success.

Recently public interest in recycling has escalated, and environmental issues are built into the National Curriculum from an early stage. When recycled, many materials are returned to their previous state - recycled glass, for example, becomes new glass. Garden compost is one of the few materials which starts as something completely different. So what process converts this assorted pile of decomposing kitchen scraps, weeds, dead plants, paper - almost anything that will rot - from its component parts, to a friable, dark and crumbly product, smelling of sweet earth?

Your KS2 pupils will probably know that the answer is bacteria, literally billions of them. One gram of garden compost contains more than one thousand million of these microscopic organisms. Your pupils may also know that microbes' needs are very similar to ours - air, moisture, warmth and food. These conditions are met when the right quantity and mixture of composting material is collected and piled together. The bacteria (and fungi) 'consume' the food, the population rises dramatically, the heap warms up and the composting process has begun.

Download the full resource from the link on the right.