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| Azalea shrubs thrive in acid soil. Photo credit: Takeshi Igarashr Flickr CC BY-NC-SA 2.0 |
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Palmer's penstemon is adapted to dry alkaline soils. |
Soil pH is the measure of the acidity of soil. On the pH scale, the value of 6.8 to 7.2 is “near neutral”. A pH value less than 7 means the soil is acidic, whereas pH values higher than 7 are alkaline.
Many plants grow best in soil with a pH range of 6.0-7.5. Soil pH directly affects many aspects of plant growth and health such as:
- Plant nutrient availability
- Soil bacterial activity
- Soil fungal activity
- Decomposition
- Soil borne plant disease
Changing Soil pH
Although many homeowners want to change the pH of their soil to accommodate a favorite plant, adding soil amendments often produces only a short lived change in pH. Better advice is to plant plants that are better suited for the existing climate and soil conditions. However, here are a few suggestions to change soil pH:
- To raise the pH of acidic soils add a liming material like calcium carbonate or dolomite. Mix into the top 6-8 inches of soil.
- To lower the pH of alkaline soil is much more difficult. Adding elemental sulfur can temporarily lower pH. However, this can be difficult and generally is short lived. Adding acid sphagnum peat is another alternative. Again, however, it efficacy is short lived.
Soil pH and Water-Wise Landscaping
Understanding soil pH and choosing the right water-wise plants adapted to existing soil pH will greatly increase the likelihood of plant survival. Plant quality will increase and less amendment will be needed. Disease will decrease.
Additional Resources:
Soil Quality Indicators
Soil pH for Landscape Plants
Northeast
Soil pH and Lime Requirement for Home Grounds Plantings
Southeast
Florida: Soil pH and the Home Landscape or Garden
