Research
Compost
A subject at the heart of good gardening practice, composting is an essential activity in all the Society's gardens. Composting is a biochemical process whereby organic matter is decomposed by naturally occurring organisms to produce a stable, soil-like end product. The micro-organisms generate heat as they break down the organic matter. Composting provides a means of converting waste materials from the kitchen and garden into an environmentally-friendly source of organic matter which can be used throughout the garden to improve soil fertility, conserve soil moisture and enhance plant growth.
A successful compost heap
The compost heap
should contain a mixture of woody, carbon-rich waste such
as prunings, wood chippings, straw or dead leaves, and softer,
nitrogen-rich materials such as grass-clippings, kitchen vegetable
waste or horse manure. In practice gardeners add whatever
waste is available at a particular time of year.
- Avoid letting any one material dominate the heap.
- Chop up woody material to encourage it to decompose more quickly.
- Avoid putting diseased plants, perennial weeds and seed heads containing mature seeds on the compost heap.
- Avoid composting cat and dog waste as they pose a health risk to humans. Manures and bedding from herbivores and birds are acceptable.
- Avoid composting plant material recently treated with herbicide. Although composting can break down most organic chemicals, some residues can persist, especially if the composting process is inefficient.
Compost usually takes about six months to reach maturity. It should be dark brown, with a crumbly soil-like texture and a smell resembling damp woodland. The top may be dry and undecomposed, and the bottom wet with a bad odour, but these can be separated out and recomposted.
Turning a compost heap
The composting process is said to be aerobic (requiring air). In situations where the compost heap is very wet, or densely compacted, oxygen levels become depleted. This leads to anaerobic (without air) decomposition occurring. This is a slower process and does not generate the same heat, so that some weeds and seeds may remain in the compost. Turning of the compost heap, although laborious, is beneficial because it promotes aeration.
Note for potting up: Composted material can be used for mulching and soil improvement, but is rarely successful for propagating new plants. A number of pre-prepared composts are commercially available, and are more suitable for seed sowing and potting up.
Home composting leaflet
Home composting research - for information on work at RHS Garden Wisley click here
Further reading
This is just one topic covered by the Society's monthly journal for Members, The Garden, and a recent article of interest is listed below.
Pickering, J 2000. Waste not, want not. The Garden (RHS) 125 (2): 106-109.
Links
Centre for Alternative Technology
See also: