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What is Compost?
Compost is created when micro-organisms feed on organic materials and begin the biological process of breaking them down into a form that plants and soil organisms can reuse. Heat in compost is generated by the metabolism of the micro-organisms that are eating the plant material. Look for compost that has been heated to at least 130F, which kills seeds, insects and plant pathogens. This same process also breaks down the chemical compounds in insecticides and herbicides that may be on the plant material. Residual heat in compost will dissipate when it is spread or tilled, but the compost will still be alive with beneficial microorganisms. Remember that it is the soil that feeds the plants, and compost feeds the soil. Compost supplies organic matter to feed the soil organisms that are necessary for plant health.
In New Mexico, our soils are generally deficient in organic material and microbial life and are alkaline (pH 7-14). We have either sandy (relatively large particle size) or clayey (relatively small particle size) soils. Compost is effective in improving any soil conditions. It breaks up clay soil and improves drainage, aeration, and tilth. In sandy soils it reduces drainage and conserves water and nutrients.
How to Apply Compost
As a general rule, blend enough compost to achieve a 50-50 mixture between the compost and the existing soil, down through the root zone. For example, if you spread compost 3" thick over a planting area and till it into the top 3" of soil, you get a 6" deep planting bed with a 50-50 mixture. Some plants, such as vegetables or prized ornamentals, may require a richer mix while some natives require very little soil amending. You can also make a "compost tea" to apply as a soil drench or foliar spray. For detailed advice on specific plants consult your nursery or horticulturalist. One cubic yard of compost will cover 108 square feet when spread 3" thick.


(information courtesy of Soilutions, Inc.)
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