Successful composting is the backbone of organic gardening, says Michael Littlewood.
Composting is vital to the functioning of an organic garden. It is an important way to recycle such elements as carbon, nitrogen, oxygen, sulphur, calcium, iron, phosphorus, potash and trace minerals, and to support populations of micro-organisms – all of them essential to maintaining the biological cycles of life in our gardens. The purpose of making compost is to process all organic waste materials into a form that can be easily incorporated into the soil, where it provides that vital ingredient known as humus. It also hastens the process so that the material is available to the gardener in sufficient quantities throughout the year.
It is far better to compost plant and animal wastes than to dig them into the soil or leave them on the surface as a mulch. Digging in uncomposted materials could result in nitrogen depletion, and material left on the soil surface can act as a breeding ground for pests and diseases. It also looks unsightly.
Compost is much better for the soil than chemical fertilisers, which do not add any organic matter and which can leach out of the soil if not used immediately by plants.
Aerobic composting
In an aerobic ‘hot heap’, a pile of plant and animal wastes generates heat and is worked on by a range of micro-organisms until it is converted into humus. This is the quickest way to make compost. A hot heap is achieved by filling an insulated container with a large quantity of material in one go. Almost any organic materials can be used, though it is important to balance carbon-rich and nitrogen-rich ingredients. The container needs to be a minimum of one cubic metre in size – small bins are inappropriate for this method as they cannot contain the heat for very long.
The decomposition process is carried out by a succession of microscopic organisms including bacteria and fungi, and larger organisms such as earthworms. When suitable materials are gathered together, these ‘compost workers’ move in to start the process. One result of this activity is that heat is produced. A large heap can reach a temperature of 60C (140F) in just a few days. This will kill weed seeds, pests and diseases. The heap will need to be turned once or twice during the process, and the compost will be ready in two to six months.
Where there are insufficient materials to make a hot heap, the cold method is used. Materials are added as they become available until the container is full. It will not heat beyond 32C (90F), takes longer to decompose, and needs to be turned more frequently.
Four key things are required in an aerobic heap:
= Air: beneficial bacteria need air, so materials should be piled up fairly loosely.
= Moisture: soil organisms require water to keep them alive, but not too much or they can drown! The heap should be like a well wrung-out sponge.
= Materials: the greater the variety of materials the better, as this will encourage a greater variety of microbial life and produce a higher quality of compost.
= Warmth: micro-organisms are most active during the warmer months of the year.
Compost activators can be used in the colder months.
Anaerobic composting
Composting anaerobically – without air – is also possible, though less usual. This process usually takes place in sealed containers or covered piles. It requires very little attention and does not need to be turned. The carbon:nitrogen ratio is not important, and no activator is required. On the downside, it is not suitable for tough or diseased material, and will not kill weed seeds and roots. It takes approximately one year to produce compost, and the quality is not as good as that from an aerobic process.
By Michael Littlewood - www.ecodesignscape.co.uk.
Picture - Cockington Cour.
