It is always best to choose plants that thrive in the pH of your existing soil. However, if you must alter the pH, follow the guidelines below. Raising your PH (Reducing the acidity)
• Use ground limestone to raise the pH of acidic soils. Limestone is nature’s soil sweetener, capable of neutralizing overly acidic soils. Remember that limestone will need time to dissolve into your soil and as such, it is best to add limestone in the fall to allow time for it to do its job.
The amount of limestone you use will vary depending on the results of your soil test. If you arbitrarily dump limestone on soil, you run the risk of overdosing the soil. Be sure to follow the instructions on the limestone package or on a soil test.
Lowering your PH (Reducing the Alkalinity)
• To lower the alkalinity and increase the fertility of limey and other soils with very high pH, add cottonseed meal, sulfur, pine bark, compost, or pine needles. These additives gradually break down and increase acidity of the soil while improving its texture. Garden sulfur is a reliable cure when added as recommended in a soil test. It acidifies the soil over time as microbes convert the sulfur to sulfuric acid and other compounds. Maintaining the new and improved pH is an ongoing project. Recheck the soil’s pH every year and continue to add amendments as needed.