Sulphuric Acid to Lower the pH of Soil

Soil pH and Plants

• The pH value of a soil affects the availability of plant nutrients in the soil, which in turn affects the overall quality of a plant's growth. Soil pH can be too high due to your geographical location; some soils in the Southeast, for instance, are naturally alkaline. Some soils have a high soil pH because they have been overworked with additives that raise pH, such as lime. Lowering your soil's pH into an optimal range for the type of crop you are planting can be achieved by adding sulphur.

Plants That Require a Low pH

• Some flowering plants, including azaleas, ixora and gardenias, grow best in soil that has a low pH level of 4.5 to 5.5. Blueberry plants also prefer a soil with a pH of 4.5 to 5.5. Plants such as these that require a low pH do poorly in high pH soils. They may develop cholorosis, an iron deficiency induced by high soil pH.

Lowering pH

• Soil pH can be lowered with organic materials, such as pine needles or peat moss, but the process will take many years. For rapid results, sulphur is preferable. Sulphuric acid forms in the soil when sulphur is added, lowering the pH. It is still a slow process, however, and can take one to two years to achieve.

Adding Sulphur

• It is best to work sulphur into the soil in the spring, when the soil is moist and warm; this will help promote the conversion of the sulphur by bacteria present in the soil into sulphuric acid. The amount of sulphur required will depend on the soil texture and the pH of the soil before the sulphur is added. Less sulphur is needed in soils that are sandy, for instance, than those that are high in clay content.