Composting
What is Composting?
Composting is the breakdown (or decomposition) of organic matter in a maintained heap. Compost is a dark, soil-like material, primarily composed of decomposed organic matter. Composting is a great way to recycle your garden and kitchen waste and help to maintain the organic matter levels in your garden in the process, ensuring that your soil is healthy.
Successful Composting
A healthy compost requires the following:
- Air (oxygen) - benefical organisms for the breakdown of material are aerobic so well aerated conditions are essential!
- Water - decomposing organisms need moist material to live in and eat. If it is too dry then they can also become inactive. If too much water is present then the air is replaced which impacts on benefical organisms. Once the compost is moist enough then a shelter or cover can help to maintain the moisure level as well as retain heat.
- Organic matter - to provide an optimum balance of nutrients, water, and aeration, it is helpful to distinguish between 'green' and 'brown' materials. 'Browns' are woody, dry, and carbon rich materials. 'Greens' are soft, lush, nitrogen-rich materials. Ideally, 'green' and 'brown' should be combined in approximately equal measure.
- Accelerators or activators - essentially nitrogen fertilisers for when there is not enough 'green' material available.
- Shredding - the smaller the source material, the faster the rate of decomposition. Shredding can also increase the surface area, helping to make more of the material accessible to organisms. Shredding too fine should be avoided to ensure that aeration is maintained and waterlogging avoided.
- pH - avoid a mix that is too acid. Thin layers of lime can be added as the heap is created.
- Temperature - the rate at which organisms decompose the organic matter depends on the temperature of their environment. The decomposition process gives off heat; under ideal conditions the temperature can rise over 70 degrees Celcius. However, most garden composts don't get to high enough temperature to kill harmful organisms and weed seeds.
- Heap size - the temperature of the heap depends on its size. If the heap is too small (< 1 m cubed) then the large surface area to volume ratio dissipates heat too readily and the heap doesn't heat up (cold composting).
- Turning - decomposing organic matter heats up quickly but the process can slow is the availability of oxygen becomes reduced. Similarly, to stirring the dying embers of a fire the decomposition rate can be restored by 'turning' the heap regularly to improve aeration.
Methods of Composting
-
Garden (home) composts - small (< one cubic metre), generally 'cold' composting. Compost bins or slatted wooden bays. A second bin is useful for turning. A suitable cover (i.e. old carpet) is is needed to keep the heat in and rain off. Can take many months or years due to slow decomposition. Take care to avoid perennial weeds or infected plant material which won't be killed by the low temperatures.
-
Hot beds - using composting to generate heat has been practiced since Roman times. The heat generated in hot bed systems was used by Victorian gardeners to grow exotic fruits such as melons and pineapples and extend the growing season into the winter. Fresh manure (typically horse) is used as a decomposition accelerator and heat generator. A loose heap, with plenty of oxygen, is created and kept moist by watering.
-
Tumblers - containers that can be rotated to provide easy turning of small batches of compost. High temperatures can be reached so weeds and diseases can be killed off.
-
Wormery - used for decomposing small quantities such as kitchen waste. Brandling or tiger worms (Dendrobena spp. and Eisenia foetida) are compost worms that feed on organic matter.
-
Municipal waste - large quantities of green waste from households and parks. A heap is formed on concrete base. Large machinery can be used for turn the material and maintain good aeration. Very high temperatures can be achieved.
Common composting materials:
- Garden waste - grass cuttings, wood prunings/chippings, annual weeds, leaves
- Kitchen waste - uncooked vegetable/fruit peelings, egg shells, tea, coffee grounds
- Farmyard manure
- Paper and cardboard (torn up or shredded)
- Wood ash (in small quantities)
Materials to avoid:
- Cooked food, meat, grease, bones, dairy produce – all can attract vermin
- Perennial or pernicious weeds
- Diseased plants
- Coal ash
- Non-biodegradable sanitary products
- Plastic, glass, metal, polythene bags – or anything inorganic
- Pet waste
Benefits of composting
- Saves money on buying compost
- Avoids peat based composts (which destroy peat bog habitats)
- Reduces waste sent to landfill
- Reduces transportation associated with council green bin schemes
- Reduces the need for garden bonfires
- Increases biodiversity in your garden
- Returns and holds nutrients in the soil
- Improves stability of the soil
- Increases water retention and drainage