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The Affects of Soil Acidity on Earthworms

Updated February 21, 2017

Earthworms are hermaphroditic annelids that help keep gardens lush and soil productive by aerating the soil. While earthworms are common in many environments, they are seldom found in highly acidic or highly alkaline soils.

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Range

Acidity or alkalinity are measured on a scale of 1.0 to 14.0 called the pH scale. A pH of 7.0 is neutral---neither alkaline nor acidic. Different species of earthworms have different preferences, but most species prefer soil with a pH between 5.0 and 7.4. This range is similar to that preferred by most plants.

Effects

Earthworms are scarce in highly acidic soils---those with a pH below 4.5. They are absent from soils with a pH below 3.5. If your soil pH is below 4.5, increasing the soil pH could help increase the number of earthworms. Earthworms don't like highly alkaline soils either, however, so don't increase the pH above their preferred range.

Theories/Speculation

Low soil pH could affect earthworms in one of two ways. Low soil pH may have deleterious effects on an earthworm's physiology, or it could be that low pH denies the earthworm some of the nutrients it needs. It isn't currently known which of these two factors is more important in determining earthworm pH preference.

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About the Author

Based in San Diego, John Brennan has been writing about science and the environment since 2006. His articles have appeared in "Plenty," "San Diego Reader," "Santa Barbara Independent" and "East Bay Monthly." Brennan holds a Bachelor of Science in biology from the University of California, San Diego.

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