Covering the ground with a layer of mulch serves three functions. First, the mulch acts to reduce water loss through evaporation; second, it helps prevent weeds from establishing and, third, it can alter the temperature just above the ground surface – something that may promote plant growth.
Organic, biodegradable mulches are best, improving soil structure and supplying plants with additional nutrients. These enter the soil through the community of decomposer organisms, which break the mulch down and make the nutrients more widely available. A mulch (such as that provided by leaf mould, compost, well-rotted manure, lawn mowings or chipped wood) is best used in a layer that is at least one inch in depth. This will provide the desired water retention benefits but a thicker layer (say four inches) is needed if the aim is to prevent weed establishment.
It is best to leave a gap around the base of each plant so that it does not become damp and subject to rot or disease. Think about where and why you want to use a mulch and avoid using an organic mulch if you do not want to increase the fertility of your soil. Other mulches should be avoided under certain conditions – e.g. it has been suggested that cocoa shell mulches may be toxic to dogs. Mushroom compost may increase soil alkalinity.
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