Soil pH affects the ease at which nutrients are absorbed by plant roots. Some plants specifically need acidic soils in order to maintain green foliage and survive. To increase the acidity of a soil, you are lowering the pH; acidic soils have a pH reading less than 7.0. The natural or staring pH level is important to determine, because it correlates as to the amount of effort needed to lower the pH to reach the acidic level you want. Parent soil materials, rainfall and amount of organic matter affect how easily and readily you can make a soil become more acidic.
Conduct a pH test on your soil. Make multiple tests across the area you wish to modify to create a more acidic soil situation. Be aware that the soil pH may vary considerable across your property because of development fill, driveways, underground rocks and formations, as well as organic matter.
Purchase granular aluminum sulfate, which is fast-acting, or sulfur that is much slower to work, from your local garden supply center or plant nursery. Consult product labels or ask a store specialist on recommendations for the amount of product needed to treat the size of your property.
Apply the sulfur-based products according to dosages and rates directed on the label instructions. Follow them closely and accurately to avoid damage to existing plants in your landscape or a future need to correct your hasty over-application of product.
Conduct a soil pH test once again after the sulfur-based treatment, at least a week afterward. Pure sulfur applications are more slow-acting, so any pH modification may take upward of a month to be noticed.
Begin adding acid-forming soil amendments to your landscape to naturally maintain a more acidic soil regime. Using organic mulches in planting beds and composts to improve soil quality is natural way to slowly drop soil pH, reducing your need to apply aluminum sulfate, sulfur or ammonium sulfate.