Simply, when there are lots of hydrogen ions floating around, a soil is acid. If there are not many floating around, the soil is neutral or may be alkaline. The pH is measured on a scale of 0 to 14, however for the vast majority of soils in natural environments, pH ranges from 4.0 to 8.3. A pH of 7 is considered neutral, below 7 is acid, and above 7 is alkaline. The lower the pH value, the more acid the soil.
Soil acidity is adjusted upward by adding liming materials to the soil.
Some horticultural crops prefer more acid conditions, and some materials can be added to reduce pH. Therefore, plant knowledge is crucial in horticultural situations. Application of liming materials should be based on the results of a soil test. The buffer pH varies with soil mineralogy and organic matter among other things, thus it depends on the unique nature of a particular soil. The Composting Page and RotWeb offer lots of composting information . Recommendations on this web site do not endorse any commercial products or trade names.