We talk about acidity and alkalinity of the soil but often don't have a good handle on exactly what that means. Of course, these terms do not just apply to our soil. They are used to describe any chemical compound.

Technically, pH is a measurement of the concentration of hydrogen ions present. It is ranked on a 14 point scale with 7.0 being neutral i.e. neither acid nor alkaline. If the pH number is lower than 7.0 it is said to be acidic while a number higher than 7.0 is said to be alkaline or base.

The pH scale is what is called logarithmic meaning that each change of 1 unit of pH means a 10 times change. So, a pH of 6.0 is ten times more acid than one of 7.0. A pH of 5 is 100 times as acidic as one of 7.0.

Most landscape plants do best with a pH in the slightly acid range between 6.0 and 7.0. A handful of "acid loving" plants such as rhododendron, azaleas, boxwood, blueberries and pin oak need a more acid environment between 4.5 and 5.5. A handful of species, especially those from the Western part of the United States do best in an alkaline soil.

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.


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