The pH scale measures how acidic or alkaline (basic) a substance is. The pH scale ranges from 0 to 14. A pH value of 7 is neutral. pH values under 7 are considered acidic while pH values of over 7 are considered alkaline. Pure water is neutral with a pH value of 7. For plant growing purposes, pH directly affects nutrient availability. In highly acidic substances, certain nutrients such as aluminum and manganese can become more available and more toxic to the plant. In addition, important nutrients such as calcium, phosphorus and magnesium are less available to the plant if grown in low pH values (acidic). When pH values are alkaline or basic (over 7), micronutrients critical to plant growth are less available.

However, it is important to note, different plants thrive in different pH ranges.