pH is a measurement of acidity in a solution, and is calculated on a unit-less scale from 0 to 14, with 7 being neutral. Below 7 is called acidic, and above 7 is termed basic. Because soils contain water, their pH can be measured.
Soil pH is an important factor in determining what plants will grow. Most plants grow in a pH range of 4.0 to 8.0. Shrubs like blueberries do well in acidic soils with pH of 4.5-5.0. Herbs like maidenhair fern and wild leeks thrive in more neutral soils. Soils with higher pH are often called ‘rich’ or ‘sweet’ because they contain many nutrients that plants need to survive. This image shows a soil with high pH, indicated by the purple color.