Weeds as pH Indicator Plants

“Is there any way to tell if you soil is acidic or alkaline, by the weeds that grow instead of a soil sample?” Question by Barbara of Youngstown, Ohio

Answer: This is an interesting question, but sadly the answer is, not really. Still, there are some great sources that can help you easily determine your soil’s pH.

Here’s Why…

Lots of research has been done on ecological “indicator” species, but many complex factors are at play in assigning true indicator species, such as climate, topography, soil pH, soil composition, competing plant species, etc. Weeds are never assigned as indicator species because weeds quickly adapt to new environments or changes in the environment.

According to a comprehensive research piece titled Weeds as Indicators: “Weed species or communities must not be used as [soil] indicators. The use of plants as indicators for soil types was sometimes successful (Ellenberg 1951; Meisel 1960; Hilbig 1967; Kuhn 1973; Weller 1978), but often without good results and therefore followed by the conclusion that weeds cannot be used as indicators.”

Don’t despair!

The Ohio State University Extension Service offers great soil testing services (Click here to learn how). I also encourage you to check out the USDA’s Web Soil Survey (Click here to view). They have “soil maps and data available online for more than 95 percent of the nation’s counties.” Pretty cool!

I hope this helps!

Happy Gardening, Jessie


Plants are the lens Jessie views the world through because they’re all-sustaining. (“They feed, clothe, house and heal us. They produce the air we breathe and even make us smell pretty.”) She’s a garden writer and photographer with degrees in both horticulture and plant biology from Purdue and Michigan State Universities. Her degrees were bolstered by internships at Longwood Gardens and the American Horticultural Society. She has since worked for many horticultural institutions and companies and now manages communications for Sun Gro Horticulture, the parent company of Black Gold. Her joy is sharing all things green and lovely with her two daughters.

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