What Weeds Can Tell You About Your Soil Health

By Yuvraj Singh Khamare

Just about everyone has, at least at one point in time, been swept up into the battle against weeds. Whether you define them as plants out of place or simply plants unwanted by humans, every definition of weeds is based on the human perspective. It is a human value judgement of certain plant species that interfere with the desired use of land at a particular time. 

This definition ignores the important role weeds play in nature. We all know about the negative effects of weeds related to our crop yields or towards aesthetics of a space, but they have a beneficial side that plays a major part in our ecosystem.

Weeds protect and restore soil that has been left exposed by natural and human disturbances. They protect the precious topsoil that provides vital nutrients to all plants, as well as land that has been exposed to clean tillage, clear cutting, fire, flood or any other disturbance that would otherwise put it at risk of erosion by rain or wind. 

The bottom line: Weeds are mother nature's way to protect soil, replenish organic matter, absorb and recycle nutrients that would otherwise leach away and restore the biodiversity in the soil.

Weeds as an indicator of soil health

Weeds can also be a great indicator of your soil’s health. An observant landscaper can notice the subtle changes in weed populations in response to their soil management skills. They can reveal the soil pH, aeration, moisture holding capacity and even the nutrient deficiency or toxicity of the soil. 

Here are top 10 of the common weeds that can be used to read your soil health:

1. Redroot pigweed (Amaranthus retroflexus) indicates that the soil is heavily compacted by either heavy foot traffic or just high clay content. Compaction is a sign of low aeration, meaning lower oxygen for roots, soil microbes, water logging and undeveloped root system. In addition, it also shows that the iron-manganese ratio is out of balance in the soil. Redroot grows in soil that is very high in potassium and manganese and low in phosphorus and calcium.

2. Lambsquaters (Chenopodium album) indicates that the soil is high in nitrogen and potassium, but low in phosphorus. Lambsquarters prefer fertile soil to grow and it is a good marker of a rich growing soil.

3. Broadleaf Plantain (Plantago major) often grows in compacted soils with low fertility. This weed has evolved from being trampled and can grow in compacted soil.

4. Crabgrass (Digitaria spp.) grows in soil that is overall low in nutrients but specifically low in calcium.

5. Dandelion (Taraxacum officinale) indicates that the soil is low in calcium but high in potassium.

6. Purslane (Portulaca oleracea) is an indicator of rich fertile soil that is high in phosphorus.

7. Stinging nettle (Urtica dioica) is a weed that can be an indicator of a good quality soil that is high in nutrients. This plant grows in soil that is rich in nitrogen and phosphorus and that is well aerated. 

8. White clover (Trifolium repens) thrives in nitrogen-deficient soil. This is an indication that the soil is low in nitrogen and clover is working hard to add nutrients in the soil. 

9. Prostrate knotweed (Polygonum aviculare) implies that the soil is dry and highly compacted. 

10. Sow thistle (Sonchus oleraceus) is often indicative of dry, heavy, acidic, and iron deficient soil. 

Conclusion

The bottom line is that this knowledge of weeds can give us the ability to make better nutritional and management decisions.