The contribution of garden compost to the productivity of the garden can be enormous. It should be added to the soil when the rate of breakdown of the organic matter has levelled off. By this stage it should be dark, crumbly and sweet smelling.
Making garden compost
To make a compost heap build up a mixture of nitrogen rich material such as grass clippings, and carbon rich material such as bark and shredded paper, preferably in a ratio of 1:2.
Almost any vegetable waste may be composted, but never use meat and cooked foods as these attract vermin. Do not use thick layers of grass clippings as they inhibit air movement. Pruning clippings may be used, although any woody stems must be shredded first. Use only young weeds. Those with seeds or about to set seed should be burned, as should all pernicious perennial weeds.
Many materials compost satisfactorily, but addirional nitrogen will speed up the process. The nitrogen may be provided as artificial fertilizer, proprietary starter compost, or preferably as manure. Manure has the advantage of containing high levels of soil organisms. Add this as necessary to the compost heap, so that there are alternate levels of organic material and manure.
If the material in the compost heap is acidic, micro-organisms will not work efficiently-adding lime will make it more alkaline.
The Composting Process
The process of making compost generates a high temperature which encourages the natural breakdown of organic matter. It also helps to kill weeds and some pests and diseases. To heat up sufficiently a compost heap should be at least 1 cubic metre in size, 2 cubic metres is preferable. Compost reaches its maximum temperature in two or three weeks and matures in about three months. Turning the heap will speed up the process and ensures complete breakdown. An ammonia smell indicates that the compost is too rich in nitrogen. A smell of rotten eggs means the heap lacks air.
Composting may be undertaken in a non-intensive way. For example, heaps of moist leaves eventually rot down, even if they are not in a bin. No starter material is added and the heap is not turned. There will however be some material that does not break down fully-this will need to be composted again.