A: I have adapted the answer to this question from a publication titled, “Soil pH and the Landscape or Home Garden” by Shober and Denny. The full publication is attached at the end of this answer.
Vegetable gardens prefer the soil pH to be between 6.0 and 6.5. If the soil is highly alkaline (over 7) then it might be necessary to raise the pH. It is difficult to bring the pH of the soil down from an alkaline state as the soil has the ability to buffer the acid and keep the pH high. In fact, lowering the pH will probably only be lowered on a temporary basis. Much of our soils come from limestone which are naturally pH levels. When you consider the high pH of our city water or well water you can see how difficult it would be to maintain a low pH. Adding elemental sulfur will lower the pH temporarily and only at the site of application. Repeat applications will probably be necessary for best results. However, one must be careful not to add too much or too often as this can damage the plants. Never apply more than “5 to 10 pounds of sulfur per 1,000 square feet per application.” Watch the plants carefully to determine if damage is occurring. Some other choices for lowing soil pH are ammonium sulfate, iron sulfate, or aluminum sulfate. Do not use calcium sulfate [gypsum], magnesium sulfate [Epsom salt], or potassium sulfate. Some of the manures will actually raise the soil pH as they contain materials with high alkaline products. http://edis.ifas.ufl.edu/ss480