Technically, any soil that has a pH below 7.0 is considered an acid soil. Most plants grow best in a slightly acid soil with a pH in the 6.0 to 7.0 range. A few such as Rhododendrons, blueberries, boxwood, heaths, heathers, pin oak and others do best in a more acid soil in the range of pH 4.5 to 5.5. So, acidity in itself is not a bad thing in soils.

Generally speaking, the soils east of the Mississippi River tend toward an acid reaction while those to the west are more alkaline. This is due to the amount of reliable rainfall in each area. Remember that the H in pH stands for hydrogen and water is H₂0. More water equals more hydrogen.

However, you should ALWAYS run a soil test through a reputable soil laboratory such as at your land grant university to determine your particular soils pH.

Soils that are Too Acid - When the pH of a soil drops below the slightly acid level (except for the acid lovers), a chemical change takes place which makes it more and more difficult for plants to take up needed nutrients. In other words, if the soil is too acid for a particular species of plants, it will show signs of nutrient deficiencies even though a soil test will say that there is plenty of that nutrient in the soil. If the pH is wrong for that plant, it will just not take up that nutrient.

Another problem in acid soils is that some elements such as aluminum and manganese suddenly become super available to the plants. This can result in a toxic level that can damage or kill the plant outright.

Finally, microorganisms may not be able to live and thrive in an excessively acid soil. This means that they will not be able to decompose organic matter to release the elements for plant use.
 

Making Soil Less Acid - Adding lime to the soil will raise the pH level. However, you must do a soil test to determine how much and what kind of lime to apply to make the desired change in pH. The amount you apply will be based on the amount of clay in the soil and the chemical buffering capacity of that particular soil. You cannot just guess on how much lime to apply to change the pH from 5.4 to 6.5. Soil test!
 

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.