How to Adjust Soil PH

How to Adjust Soil PH

Soil pH measures how alkaline or acidic the soil is. The pH scale is from 0 to 14 with neutral being 7 on the scale. Acidic soil is anything with a pH value less than 7 and alkaline soil is anything with a pH value over 7.

Plant Growth

The quality of plant growth and reproduction is affected by the pH level of the soil and the requirements vary depending on the plants themselves. The pH value is directly related to how available nutrients in the soil are for the plants. Different plants require different pH levels. Azaleas and blueberries are at their best in acidic soils with a pH between 5 and 5.5. Grasses, ornamental flowers, and vegetables prefer a slightly acidic soil with a pH between 5.8 and 6.5. Nutrient deficiencies may result of the soil pH is above or below the recommended range.

Soil pH

 values above or below these ranges may result in less vigorous growth and nutrient deficiencies.

Three are 3 categories of nutrients

required for healthy, productive plants and vegetables. Nitrogen, phosphorus and potassium are the primary nutrients and are needed in much larger quantities than other the secondary or micronutrients. The secondary nutrients, magnesium, sulfur, and calcium are needed in much smaller quantities but are still very important to the health of the plants. The micronutrients, manganese and zinc are required in small amounts. For the most part secondary and micronutrients can be controlled by maintaining the soil pH at the proper level. The primary nutrients are controlled by adding fertilizer.



Plant growth is impacted by the availability of nutrients which is affected by the extremes of the pH. Some nutrients become toxic to plants when they are more available to them such as aluminum or manganese in highly acidic soils. At low pH values, calcium, phosphorus and magnesium become less available for the plant to take up. When the soil pH is above 6.5, most of the micronutrients are less available to the plants.

Several things factor in to the level of pH in the soil. Soil formed by basic rocks typically has a higher pH than soil formed by acid rocks.

If soils are formed in high rainfall areas they will be more acidic than those formed in dry areas. This is due to the rainfall leaching nutrients from the soil and depositing aluminum and iron which are acidic. Decomposing organic matter and fertilizers containing ammonium or urea increase the acidity of the soil.

To increase the soil pH value ground limestone is commonly used. How much limestone is needed to raise the pH value depends on several things including how much organic matter there is and the texture of the soil. Typically the more clay there is in the soil the more limestone will be required to adjust the pH value of the soil.



You should always have your soil tested prior to trying to make any adjustments. Your local Agricultural Extension Agency should be able to provide you with soil testing services and a detailed report. Have your soil tested in the fall and add the required amount of limestone 2 or 3 months before planting.

Wood ashes

are also used to raise the pH of the soil although they are not as effective as limestone. Work small amounts of wood ash into the soil during the winter months.

If you need to lower your pH, based on a soil test, apply sulfur or aluminum sulfate. Sulfur will convert over time into sulfuric acid taking longer to affect the pH than aluminum sulfate which works instantly.