Soil is considered alkaline when the pH is higher than 7.0. The pH scale is a measure of hydrogen ions in a solution. Anything below 7.0 is acidic, anything above 7.0 is alkaline; 7.0 is neutral. Alkaline soil can be a problem for plants and trees that need soil that's more acidic. To lower the pH of your soil, begin by purchasing an inexpensive pH soil-test kit as well as some garden sulfur, which are both available at most hardware stores and garden supply stores.
Things You'll Need
Soil pH test kit
Take soil samples from several different areas on your property.
Place the soil samples in your pH test kit's tube. Add the test solution.
Shake up the test tube. Let it settle for about an hour.
Check the color of your test tube's solution. Compare it to the pH test chart to determine the pH of your soil.
Distribute the garden sulfur evenly across your soil in the amounts recommended by the manufacturer. The directions on every bag of garden sulfur will recommend a specific amount of sulfur per 100 square feet of soil, based on the current pH of your soil and how much you want to lower the pH. The results of your pH test kit will determine how much garden sulfur should be added to reach the desired pH level.
Test the pH of your soil several more times over the next few months to determine if the sulfur has reduced alkalinity to the desired level. Do not add more sulfur until two to three months have passed and your pH testing kit shows that pH levels have stabilized.
You can also use coffee grounds, sawdust, peat moss and cottonseed meal to lower the pH of your soil. Simply add these items directly to the soil or, to lower alkalinity more efficiently, mix them with your compost pile and apply the compost to your soil.
To avoid harming your plants and trees, never apply more than 2 pounds of sulfur per 100 square feet. Avoid using aluminum sulfate, which is toxic to humans, to lower the pH of your soil. Sulfur works more slowly, but it's safe and nontoxic to humans.