"Basic" and "Acidic"

In purely chemical terms, basic describes a substance with a pH greater than 7 (such as baking soda), whereas acidic describes a pH of less than 7 (such as vinegar). Soil scientists and geologists use this definition to describe the chemistry of soils and rocks.

Ecologists, however, often use the term "basic" to describe soils in which most plants flourish. Rather than being truly basic, they are relatively less acidic. They can form, for example, over bedrock that contains enough calcium or other base elements to positively influence plant growth.

Bloodroot (Sanguinaria canadensis) is one spring wildflower that flourishes in acidic soil with adequate base elements.
Photographer: Gary Fleming
With adequate calcium, even acidic soils are able to support natural communities such as the Basic Mesic Hardwood Forest that have a wide variety of plants, even those with high nutrient demands. Gardeners are familiar with this concept: they add lime (a base) to acidic soil to raise the pH of the soil to between 6.2 and 6.8—the optimal, though still slightly acidic, range for most vegetables and flowers. In contrast, soils with a pH greater than 7.5—truly basic soils—can be toxic to many plants.

In Explore Natural Communities, we refer to lush, nutrient-demanding natural communities themselves as “basic,” regardless of the soil they grow on. However, for clarity, we will refer to soils (or their parent rocks) as “basic” only if their pH is above 7.0. Soils that are good for plant growth we will refer to as “nutrient-rich,” “fertile,” or “rich.”