Acidic soil is commonly referred to as being "sour" and tends to have mineral deficiencies that can affect plant growth. By definition, acidity is the characteristic of soil that has a pH level of less than 6.5 (a reading of 5.5 means the soil is very acidic). Readings over 7 or 7.5 indicate alkalinity.

What is Acidic Soil? Soil is acidic when it’s pH value is below 7. Some plants actually prefer slightly acidic soil, but extremes (on either end of the pH scale) are bad news for your plants.

Acid soils are those that have a pH value of less than 5.5 for most of the year. They are associated with a number of toxicities (Aluminum) as well as deficiencies (Molybdenum) and other plant restricting conditions. Many of the acid soils belong to Acrisols, Alisols, Podzols and Dystric subgroups of other soils.