Soil pH is an important factor in gardening because it regulates the availability of nutrients to plants. Most plants prefer a pH between 6.0 and 7.2, but some plants such as blueberries and azaleas prefer even lower pH levels. You can test your soil pH with kits that are sold at most garden centers. Test the soil at least three weeks before planting to make sure the soil has time to adjust to any amendments you apply.
Elemental Sulfur or Iron Sulfate
Test the soil with a soil pH testing kit to determine the current pH level.
Follow the amendment instructions supplied with the soil test kit to lower pH. Typically, to change the soil pH from 7.5 to 6.5, add about 1.5 pounds of sulfur per 100 square feet of soil several months before planting; to move the pH from 8.5 to 6.5, use about 4 pounds. If you use iron sulfate instead, apply it several weeks before planting and add 12.5 pounds per 100 square feet to change the pH from 7.5 to 6.5 or about 33 pounds to move pH from 8.5 to 6.5.
Water the soil thoroughly or apply after a rainy day while the soil is still moist.
Apply the elemental sulfur or iron sulfate evenly to the soil. Mix it into the top 6 inches of the soil with a hoe or tiller.
Test the soil pH after three or four months if you used elemental sulfur. If you used iron sulfate, test the soil after three or four weeks. Reapply the amendments as needed.
Test the soil pH with a soil pH testing kit.
Till the soil or break it up with a hoe to a depth of 6 inches.
Apply 2.5 pounds of peat moss, 14 pounds of compost or 5 pounds of manure per 9 square feet to the soil to reduce the pH by one point.
Till the soil or mix in the amendments with a hoe.
Test the soil after three or four weeks. Add more amendments as needed.