Soil pH changes are brought about by bacterial action. Bacteria need a
minimum of 3% organic matter (humus)
to do their work best. Testing your pH can be done by a soils lab but if
you use your own pH meter, the soil
must be thoroughly saturated with distilled water before taking a reading.
Once your soil is properly acidified,
maintain acidity with Ammonium Sulfate. For best results, soil should be
acidified at least one season before
planting because acidification is a slow process. Though it acidifies much
faster than Elemental Sulfur,
Aluminum Sulfate is not recommended for use. (There is a similar chart for
elevating pH in soil.)