Compost is the aerobically decomposed remnants of organic matter. It is used in landscaping, horticulture, agriculture as a soil conditioner and fertiliser. It is also useful for erosion control, land and stream reclamation, wetland construction, and as landfill cover. Compost serves as a growing medium,or a porous, absorbent material that holds moisture and soluble minerals, providing the support and nutrients in which most plants will flourish. To maximize plant growth, it is sometimes necessary to dilute compost with soil or peat to reduce salinity or to add neutralisers to bring the pH closer to 7, or additional nutrients like fertilisers or manure, wetting agents, and materials to improve drainage and aeration, such as sand, grit, bark chips, vermiculite, perlite, or clay granules.

As concern about landfill space increases, worldwide interest in recycling by means of composting is growing, since composting is a widely accepted process for converting decomposable wastes of biological origin into stable, sanitized products useful for horticulture. 

There are different ways to compost, starting with layers of ‘brown’ and ‘green’ biodegradable waste mixed with garden soil. ‘Brown’ waste refers to old straw, tough vegetable stems and hedge clippings. ‘Green’ waste refers to biodegradable waste that breaks down faster, such as fruit, cut flowers, and grass clippings. There is also Vermicomposting, which uses worms to help break down the organic waste.

Composting recycles or “downcycles” organic household and yard waste and manures into an extremely useful humus-like, soil end-product called compost. Examples are fruits, vegetables and yard clippings. Ultimately this permits the return of needed organic matter and nutrients into the foodchain and reduces the amount of “green” waste going into landfills. Composting is widely believed to speed up the natural process of decomposition appreciably as a result of the raised temperatures that often accompany it. The elevated heat results from exothermic processes, and the heat in turn reduces the generational time of microorganisms and thereby speeds the energy and nutrient exchanges taking place. It is a popular misconception that composting is a “controlled” process; if the right environmental circumstances are present the process virtually runs itself. Hence a popular expression, “compost happens”. It is nonetheless very necessary to provide as optimal circumstances as possible for large amounts of organic waste to break down properly. This is especially so when it is accompanied by heating, since at elevated temperatures oxygen within the piles is consumed more rapidly, and if not controlled, will lead to malodor.

Decomposition similar to composting occurs throughout nature as garbage dissolves in the absence of all the conditions that modern composters talk about; however, the process can be slow. For example, in the forest bark, wood and leaves break down into humus over 3-7 years. In restricted environments, for example, vegetables in a plastic trash container, decomposition with a lack of air encourages growth of anaerobic microbes, which produce disagreeable odors. Another form of degradation practiced deliberately in absence of oxygen is called anaerobic digestion- an increasingly popular companion to composting as it enables capture of residual energy in the form of biogas, whereas composting releases the majority of bound carbon-energy as excess heat (which helps sanitize the material) as well as copious amounts of biogenic CO2 to the atmosphere.

It is important to distinguish between terms such as “biodegradable”, “compostable”, and “compost-compatible”. A biodegradable material is capable of being broken down completely under the action of microorganisms into carbon dioxide, water and biomass. It may take a very long time for a material to biodegrade depending on its environment (e.g. hardwood in an arid area), but it ultimately breaks down completely.

A compostable material biodegrades substantially under composting conditions, into carbon dioxide, methane, water and compost biomass. Compost biomass refers to the portion of the material that is metabolized by the microorganisms and which is incorporated into the cellular structure of the organisms or converted into humic acids etc. Compost biomass residues from a compostable material are fully biodegradable. “Compostable” is thus a subset of “biodegradable”. The size of the material is a factor in determining compostability because it affects the rate of degradation. Large pieces of hardwood may not be compostable under a specific set of composting conditions, whereas sawdust of the same type of wood may be.

A compost-compatible material does not have to be compostable or even biodegradable. It may biodegrade too slowly to be compostable itself, or it may not biodegrade at all. However, it is not readily distinguishable from the compost on a macroscopic scale and does not have a deleterious effect on the compost (e.g. it is not a biocide). Compost-compatible materials are generally inert and are present in compost at relatively low levels. Examples of compost-compatible materials include sand particles and inert particles of plastic

1. 4mm Potting compost/turf dressing
2. 10mm Soil conditioner for horticulture, soft landscaping/gardening use
3. 25mm Soil conditioner for bulk agricultural use
4. Mulch for weed supression on beds and borders