Garden Myths Gardening Weeds

Garden Myth: Weeds that Indicate the Soil’s pH

Dandelions, like most weeds, will grow in pretty much any soil. Photo: Sergeant, depositphotos

By Larry Hodgson

Many gardeners claim that you can tell the pH of your garden’s soil (its acidity or alkalinity) just looking at the weeds that grow there. Mosses, ferns, horsetails, dandelions and hawkweed, they say, only grow in acidic soil while wild carrots, goosefoots, bladder campions, and thistles indicate an alkaline soil. In fact, there is even a term for this: indicator plants or bioindicator plants.

There’s just one problem: it doesn’t really work for soil pH.

In fact, all the aforementioned plants grow equally well in soils that are on the exact opposite of the spectrum (mosses in alkaline soil, thistles in acid soil, etc.). Even a cursory glance at the weeds in your own yard will probably show dandelions and wild carrots growing side by side, or thistles near hawkweeds. In fact, the ability to grow in almost any soil is a characteristic common to most of the plants we call weeds.

Thus, the presence of a particular weed does not indicate much of anything … except that it is perhaps time to do a little weeding.

If you really want to know the pH of your soil, just have your soil tested.

Article originally published on April 19, 2016.

Garden writer and blogger, author of 65 gardening books, lecturer and communicator, the Laidback Gardener, Larry Hodgson, passed away in October 2022. Known for his great generosity, his thoroughness and his sense of humor, he reached several generations of amateur and professional gardeners over his 40-year career. Thanks to his son, Mathieu Hodgson, and a team of contributors, will continue its mission of demystifying gardening and making it more accessible to all.

4 comments on “Garden Myth: Weeds that Indicate the Soil’s pH

  1. Ha! I was thinking exactly that as mu soil is alkaline and has a preponderance of dandelion and hawkweed.

  2. We have very acidic soil, so the reason we get soil test is to see if we have moved the pH & how much.
    Your answer is garden 101, which is why it is missed so often.
    You should get a soil test once every five years or more often if you have problems.

  3. Although, there are a few weeds that survive in situations that are too wickedly alkaline for other plants to survive in. However, such alkalinity would be obvious prior to the identification of the weeds that are lacking.
    In the Santa Clara Valley, old hydrangeas that exhibit color are naturally pink. If they start out blue, they turn pink. (However, some of the modern colorful cultivars express their preferred colors more reliably than old cultivars, and do not change so easily. White hydrangeas should remain ‘generally’ white.) In this region, even though the soil is alkaline, hydrangeas can be blue because of the redwood debris. They are marginal enough that we can modify the color relatively easily with appropriate fertilizers. We prefer for some to be blue, and for others to be pink.

  4. Alan Blackwell in West Australia.

    So true!! Dandelions grow readily in almost pure limestone. By my opinion lack of Dandelions indicate it’s probably a desert.

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