As a gardener, there are times you need to alter your soil’s pH to make it more acidic or more alkaline.
A soil’s pH is the measure of its acidity. A pH of 7.0 is considered neutral between an acid and an alkaline soil. To the degree that the pH is above 7.0, the soil is alkaline; to the degree that the pH is below 7.0, the soil is acid. As a rule of thumb, soils in dry climates are more alkaline, and soils in moist climates are more acid.
This is relevant to the gardener because different plants need different levels of acidity in the soil to thrive. Azaleas, blueberries, and gardenias, for example, prefer an acid soil.
So for anything you intend to grow, you need to research its preferred pH range. Then test your soil to make sure it is in that range. There are pH test kits for do-it-yourselfers to test your soil’s pH, or you can have a sample of your soil tested at most garden centers where you buy your supplies.
If the pH is not where you need it to be, you can amend the soil to alter its pH. In order to raise a soil’s pH and make it more alkaline, you can simply add lime. But what if the pH is too high, and you need to make it more acidic?
There are many natural substances you can mix in your soil to lower the pH. These include composted leaves, cottonseed meal, leaf mold, peat moss, sawdust, and wood chips.
Some fertilizers are heavy in sulfur. Choosing these will lower the pH of your soil.
You can also mix ground rock sulfur directly into your soil. You’ll need less for a sandy soil. The general formula is that each 1.2 ounces of sulfur per square yard will lower a sandy soil’s pH by approximately one full point, whereas other soils will need about three times that much sulfur for the same effect. Be sure to mix the sulfur into the soil thoroughly.
Especially if you are seeking to alter the pH of your soil significantly, it is recommended that you do so gradually, over multiple seasons, rather than trying to do it all at once.
Another option to consider if your soil is far from the range of acidity you need is to bypass it entirely by building a raised bed and using the appropriate soil purchased from a garden center.
Charles C. Mitchell, Jr. and James F. Adams, “Lowering Soil pH.” Clemson Extension.
“A Guide to Testing and Adjusting the pH of your Garden Soil: How to Correct your Soil Acidity or Alkaline Soil.” The Garden Helper.