Compost is organic matter that has been decomposed for use as fertiliser and soil conditioner.
At its simplest, composting can be done by accumulating a pile of wetted garden and food waste and allowing the micro-organisms and worms to do their work of breaking it down. Organic matter can be added to the garden in four ways:
- Cold compost is the easiest method as material is simply added to the heap as it becomes available. A mix of 'green' (soft plant matter and kitchen scraps) and 'brown' (fibrous materials like paper and woody plant matter) needs to be included to give a good carbon:nitrogen ratio. The heap should be kept moist but not wet. Cold composting takes 1--2 years.
- Hot compost is the quickest method and produces the best compost, but is a more exacting process. The heap needs to be a minimum 1m cubed. Gather all the material to fill the heap and add all in one go. Include a good mix of 'green' and 'brown' materials. Mix well. Turn the heap every few weeks until it stops heating up and then leave to complete composting process. This can be achieved in as little as two months in the summer.
- Worm compost (vermicomposting): a wormery is a mini-compost heap filled with the same worms found in larger traditional heaps (i.e. brandling worms- the thin red ones) and are most useful for households with a small (or no) garden, and where kitchen waste (i.e. 'green' matter) is the main material to be composted. It is usually possible to harvest worm compost about every four to nine months. Through the action of worms the wormery produces solid compost known to gardeners as 'black gold', and concentrated liquid feed (which should be diluted before adding to the garden).
- Uncomposted mulch. Adding 'green matter' to the soils surface is a good alternative to making compost. Most soil microbes live near the surface of the soil and need feeding. Surface mulch also promotes earthworm activity which is beneficial for soil health. However, care needs to be taken not to add uncomposted mature plant matter such as woody stems, wood chips or straw as these can cause 'nitrogen robbery' from the soil. The decomposition of organic matter requires nitrogen to occur and this will be taken from the soil if there is not sufficient nitrogen in the mulch (as there is in sappy green plant matter) and this may cause yellowing of plant leaves. Eventually this will sort itself out once all the mulch has decomposed, but may last a season or two. Most uncomposted manure should not be added directly to soil as it may 'burn' plants.