Effects of Acidic Soil on Plants

Plant Soil Preferences

• Most plants do well in a pH between 5.5 and 7.5. Different plants react to pH in different ways. Most plants grow best in soils with a pH between 6 and 7.5. Some plants, such as azaleas, rhododendrons and blueberries prefer acidic soils with pH values between 5.5 and 7. In general, a pH below 5.6 is considered too low for most plants, lacking key nutrients such as calcium and phosphorous.

Effects of Acidic Soil on Nutrients

• Variations in pH affects the availability of plant nutrients because the nutrients must be dissolved in water to reach the plant. High-acid soils may have plenty of calcium, phosphorus and magnesium in the soil, but the plant's use of the nutrients is stifled because they are not soluble in acidic conditions. Additionally, some toxic metals become more soluble and can cause problems or even kill plants.

Acid Soils and Micro-organisms

• Acidic soils also affect the activity of micro-organisms in the soil. Micro-organisms in the soil are necessary to break down organic material and free nitrogen and other nutrients for plant use. These micro-organisms thrive in a pH range of 6.6 to 7.3. Any harm to these beneficial organisms increases the risk of plant diseases from lack of nutrients or from an overgrowth of harmful micro-organisms.

Correcting Acidic Soil

• When soil is too acidic, there are a number of things that can be done to correct the problem. The most common remedy is to add lime to the soil in the form of pure calcium carbonate, dolomitic lime or hydrated lime. Lime is approved for use on organic gardens as a certified organic product. Soil testing determines how much lime to use and whether other corrective measures are needed. Lime is usually added once, then further testing is needed before adding it again. Testing every 2 years is usually sufficient.

Causes of Acidic Soil

• The pH of the soil is affected by a variety of conditions. The natural makeup of the soil is important along with its weathered condition. Soils with natural sulfur content tend to be acidic. These conditions are often caused by mining activities nearby or current or previous tidal flat conditions. The addition of ammonium fertilizers also increases the acidity of the soil. Additionally, removal of natural bases such as calcium, potassium and magnesium, help to acidify the soil.