Soil pH Modification

Gardens & Landscapes March 14, 2014|Print

Adapted from Carl J. Rosen, Peter M. Bierman, and Roger D. Eliason. Department of Soil, Water, and Climate. University of Minnesota.[1]

 

Soil pH and Nutrient Availability

Figure 1. Nutrient availability and microbial activity as affected by soil pH; the wider the band, the greater the availability or activity. (Adapted from Truog, USDA Yearbook of Agriculture 1943-1947)

Soil pH is an important chemical property because it affects the availability of nutrients to plants and the activity of microorganisms in the soil. Soil pH is a measure of soil acidity. A pH of 7 is neutral, a pH below 7 is acid, and a pH above 7 is alkaline. The pH of urban landscapes may be higher than corresponding native undisturbed soils because of the large amount of cement used during construction. A pH measurement is therefore an important part of a soil testing program. The effect of pH on microbial activity and nutrient availability in mineral soils is shown in Figure 1.

While many plants can tolerate pH ranges between 5.2 and 7.8, most plants grow best in mineral soils when soil pH is between 6.0 and 7.0 (slightly acid to neutral). This general rule applies to most of the commonly grown fruits, vegetables, flowers, trees, and shrubs. Most turfgrasses tend to grow best between 5.5 and 6.5. Many evergreen trees and shrubs prefer a pH range of 5.0 to 6.0. Potatoes tolerate a wide range in soil pH, but potato scab can be a problem if the pH is above 5.3.

Some noted exceptions include blueberries, azaleas, and rhododendrons (acid-loving plants) that require acid conditions between pH 4.5 and 5.2. Blue hydrangeas also require a pH lower than 5.0 to induce the blue flower color.

The optimum pH range for plant growth in organic soils (peats and mucks) is lower than the optimum range in mineral soils. For many plants, the most favorable range in organic soils is pH 5.4 to 6.2.

If a soil test indicates that soil pH is not in the optimum range for the plants you wish to grow, use the following recommendations to either raise or lower the soil pH.

Raising and Lowering Soil pH

Find guidelines for raising and lowering soil pH, including amounts of material to use, timing, and methods of application, at:

Credits

  1. Rosen, C. et al. Soil pH Modification. 2004. Soil Test Interpretations and Fertilizer Management for Lawns, Turf, Gardens, and Landscape Plants. http://www.extension.umn.edu/distribution/horticulture/components/1731-03.html. University of Minnesota. (accessed January 15, 2008).

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