Soils are referred to as being acid, neutral or alkaline, depending on their pH levels. A logarithmic scale is used to measure soil pH. That is, a change of one unit in the pH scale represents a 10-fold change in acidity or alkalinity. A soil with a pH of 5.0 is 10 times more acidic than a soil with a pH of 6.0 and 100 times more acidic than a soil with a pH of 7.0. This is one of the major reasons to use caution when attempting to raise or lower soil pH. Certain factors, including soil type and organic matter, affect the amount of materials required to change soil pH. Soil pH is affected also by the application of fertilizers and rainfall. Other factors, such as organic matter, soil texture and soil microorganisms, affect soil pH. Agricultural limestone normally is used to increase soil pH. Sulfur is normally used to lower the soil pH, but the application of fertilizer and water normally change the soil pH more rapidly.
Plants have specific pH requirements for normal growth.
Most ornamental plants grow well in a pH range of 6.0 to 7.0. Azaleas, gardenias, camellias and related plants, however, require a soil pH level between 4.5 to 6.0. It is important to know the pH levels and nutrient requirements of your ornamental plants to ensure normal growth and success. The Louisiana Cooperative Extension Service provides equal opportunities in programs and employment.