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… except that it’s not really true.
In fact, all the afore-mentioned 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.