Weeds— What They can Tell You about Your Soil

Question: My lawn-care company representative says he can tell that my soil is acid and compacted just by which specific weeds are growing in it. Do weeds really reveal the soil's condition?

Certain weeds are indeed fairly reliable indicators of growing conditions. Although a soil test is the surest way to confirm a soil's deficiencies, you can get a good idea of the growing conditions by recognizing key species.

Acid soils, for example, typically support an abundance of sorrel or sour grass (Rumex acetosella). This is a close relative of the salad herb, which has larger leaves and a more refined lemony taste.

Compacted soils tend to favor goosegrass (Eleusine indica), prostrate knotweed (Polygonum aviculare), prostrate spurge (Euphorbia supina or Chamaesyce humistrata), annual bluegrass (Poa annua), common chickweed (Stellaria media), mouse-ear chickweed (Cerastium vulgatum), and rushes (Juncus spp.). Low fertility favors legumes such as white clover (Trifolium repens) and black medic (Medicago lupulina), as well as carpetweed (Mollugo verticillata), poor joe (Diodia teres), quackgrass (Agropyron repens), sorrel, yarrow (Achillea millefolium), and yellow woodsorrel (Oxalis stricta).

In damp, poorly drained areas, look for annual bluegrass, barnyard grass
(Echinochloa crus-galli), common chickweed, ground ivy (Glechoma microcarpa), mouse-ear chickweed, moss, pennywort (Hydrocotyle spp.), rushes, sedges (Carex spp.), speedwells (Veronica spp.), and violets (Viola spp.).

The secret to reducing the abundance of any of these weeds is to change the conditions that favor their growth. Soil improvement, not herbicide, is the best way to ensure that the grass in your lawn gets an upper hand.

This post is excerpted from the July/August 2003 issue of Horticulture.

Image Credit: Wikimedia Commons

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