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University of California
UCCE Master Gardeners of Orange County
Many people are confused about the terms “compost” and “mulch;” frequently these terms are used interchangeably, but they are not really the same thing. We hope the table below will help to clarify what is meant by these terms.
||Compost is the biologically active material that results from decomposition of organic matter under controlled circumstances.
||Mulch is any material, organic or inorganic, that is spread over garden soil to cover it.
||The main benefit of adding compost to soil is improvement of soil structure. Compost is considered a soil conditioner, rather than a fertilizer, but more importantly, it can retain and make existing nutrients more readily available to plants.
||Mulch can suppress weeds, moderate soil temperatures to help keep plant roots cool and moist; conserve water; maintain a porous surface and help prevent soil erosion. An organic mulch can improve soil structure as it decomposes over time.
||Compost can be mixed in with garden soil to amend soil prior to planting and also to amend potting soils. Compost can be spread on top of the soil and used as a mulch or top dressing in planted areas.
||Mulch is spread on top of the soil.
||Compost can be prepared at home in a bin composter or can be purchased in bulk or by the bag.
A specialized form of compost results from worm composting (vermicomposting).
Organic mulches: wood chips, grass clippings, leaves, straw. Most organic mulches consist of fairly large particles, although compost can also be used as an oranic mulch. The larger the particles, the longer it will take for the mulch to break down.
Inorganic mulches : stones, gravel, landscape fabric, plastic,
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