Method 1 of 2: Increase the pH by adding Lime
Select your lime source depending on the needs of your plant. Some lime sources contain micronutrients like dolomite, which is a mixture of calcium and magnesium carbonates. Wood ashes also provide lime with the addition of other micronutrients including potassium, phosphate, boron and other elements. Standard lime comes in 4 types of ground limestone forms: pulverized, hydrated, granules and pellets.
Apply the liming source 2 to 3 months before planting (usually in the fall or winter) so there is plenty of time for the pH to change.
Mix the lime thoroughly into the soil because most liming sources are not very water-soluble.
Water the soil regularly after adding the lime. Water activates the lime source to reduce acidity.
To Make the Soil More Acidic,
Add Organic Material, Leaves, etc., and/or Add Sulfur or Aluminum Sulfate
Make an immediate decrease in the soil pH by adding aluminum sulfate, which produces instant acidity due to the aluminum content. [Rinse off any aluminum sulfate that touches plants]
Increase the soil’s acidity slowly by using sulfur. Sulfur works in conjunction with the soil’s moisture, temperature and bacteria to lower the soil pH.
Aggregate the sulfur or aluminum sulfate into the soil thoroughly.
Wash the sulfur or aluminum sulfate off any plant leaves that it comes in contact with to avoid burning the plant.