Weeds are an indicator of a soil’s health

Weeds can be a headache, but they can also be very helpful if we know a few basic principles. Weeds give us clues to the health of our soil in lawns, landscapes, gardens and pastures.

Field horsetail. Photo: Christy Sprague, MSU.
Field horsetail. Photo: Christy Sprague, MSU.

What exactly is a weed? By one definition, a weed is a plant out of place. So a stately oak or beautiful rose bush could, by this definition, be a weed if not in a proper or useful place. Merriam-Webster defines a weed as “a plant that is not valued where it is growing and is usually of vigorous growth; especially: one that tends to overgrow or choke out more desirable plants.”

Weeds can be a headache for most of us, but they can also be very helpful if we know a few basic principles. Weeds give us clues to the health of our soil in our lawns, landscapes, gardens and pastures. Although in pastures, a variety of plants including many classified as weeds will help give the animals nutrients they need.

Christy Sprague, a research scientist with Michigan State University’s Department of Plant, Soil, and Microbial Sciences, states, “Weeds can tell you a lot about soil conditions. For example, field horsetail is a good indicator of poorly drained, low pH soils. Improving the drainage and increasing the soil pH by liming will help to manage field horsetail as a weed.”

Sprague’s research and MSU Extension program focuses on integrated weed management, biology, ecology and managing emerging problematic weeds, and understanding the interactions with weeds and other pests and pest/crop management practices. Her program emphasizes weed management in soybeans, sugarbeets, dry beans and potatoes.

The following list of weeds will give you clues about your soil’s health by looking at the weed populations.

Signs of soil deficiencies:

  • Redroot weeds, such as redoot pigweed (Amaranthus retroflexus), are signs that the iron-manganese ratio is out of balance. It may indicate there is too much iron or too little manganese. It also indicates a soil that is very high in potassium and manganese and low in phosphorus and calcium.
  • Quackgrass (Elytrigia repens) is a sign of improper iron-manganese ratio.
  • Bitterweed (Helenium tenuifolium), trumpet vine (Campsis radicans), broom sedge (Andropogon virginicus), stinging nettle (Utica dioica), horsetail (Equisetum arvense) and wild buckwheat (Polygonum convolvulus) may all indicate a calcium deficiency in the soil.
  • Wild buckwheat (Polygonum convolvulus) also signifies low phosphorus and an excess of potassium.
  • Burdock (Artium lappa) indicates low calcium, high potassium soils.
  • Curly dock (Rumex crispus) loves compacted soil, low calcium and extremely high magnesium, phosphorus and pot.
  • Lambsquarters (Chenopodium album) grows in low phosphorus, high potassium soils.
  • Foxtail barley (Hordeum jubatum) likes low calcium, high magnesium, as well as compacted and poorly drained soil.
  • Knapweed (Centaurea maculosa) grows in soils that are low in calcium, humus and very low phosphorus levels.
  • Oxeye daisy (Chrysanthemum leucanthemum) prefers to grow in soils that are low phosphorus, high potassium and high magnesium soils.

To learn more about the weeds in your lawn, landscape, garden or pasture, along with pictures for identification, visit MSU’s Identifying Weeds in Field Crops and Gardening Know How’s Weed Identification Control.

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