What Weeds Can Tell Us About the Soil
Common Plants with Surprising Benefits

Recognize these weeds? If they’re growing in your garden, they may be trying to tell you something. Although we often regard weeds as troublesome interlopers, these wild plants, which love to root in areas of bare earth, offer many benefits to the garden. According to Louise Riotte, author of Carrots Love Tomatoes, a book about companion planting, weeds appear to “accumulate the nutrients in which a particular soil is deficient.” Deep taproots of such uninvited guests as dandelions and docks reach down into the subsoil to bring up minerals and moisture that have leached to levels that shallow-rooted vegetable plants can’t access. When these weeds are composted (preferably without their flowering heads), they release their accumulated minerals back into the soil.

Weeds often grow in bare areas where the soil is too poor to support other kinds of plants. In addition to concentrating minerals deficient in a particular soil into their structures, many wild plants have extensive root systems which, as they decay, leave channels for drainage, and help build humus in the ground. Some weeds can also absorb excess salt from the soil.


Weeds provide other benefits. Flowering weeds
produce pollen which attracts beneficial insects like ladybugs and bees to the garden. In early spring, this is especially helpful to vegetable beds not yet in flower. Weeds also prevent erosion, especially on steep slopes. Finally, weeds indicate the health of the soil—whether it is acidic, alkaline, compacted or fertile. By looking at the kinds of weeds in your garden, you can determine nutrient deficiencies and the general health of the earth. If you have healthy green weeds in your garden, you will likely grow good vegetables. And maybe this season you’ll add a few edibles like chickweed and dandelion greens along with your usual fare.

Common Northwest Garden Weeds

(Click to enlarge photos)

Bindweed (Morning Glory) (Convolvulus)
The presence of bindweed indicates poor drainage, often hardpan soil with a crusty surface. Bindweed grows in neglected areas and does not like cultivated soil. The roots contain minerals which can be returned to the soil when composted.




Buttercup (Ranunculus)
Thrives in poorly drained, cultivated garden soil. Creeping buttercup accumulates potassium from the soil.






Chickweed (Stellaria)
When healthy, chickweed indicates tilled, fertile soil. Chickweed often grows where the soil is cool and moist. Chickweed accumulates potassium, phosphorus and manganese which is released into the soil when it decomposes. Edible. Chickweed is sometimes used in salads. It is a source of vitamin C, B vitamins and minerals.



Clover (Trifolium)
Indicates low fertility soil, low in nitrogen. Like other legumes, clover obtains nitrogen from the air and fixes it into the soil when tilled under. Clover can be planted as a cover crop.





Dandelion (Taraxacum)
Found in heavy, clay, compacted acidic soil, but also grows in fertile well-drained soil. The dandelion’s taproots bring up calcium, iron, and a host of other minerals from the deep soil. The decomposing roots of dandelions produce humus. Flowering dandelions provide early spring pollen that attracts ladybugs and other beneficial insects to the garden. Edible. Dandelion leaves are sometimes used in salads. They are rich in beta carotene, vitamin C and vitamin A.


Dock (Rumex)
Indicates waterlogged, poorly drained soils with increasing acidity. Docks have deep taproots that bring up calcium, potassium, phosphorus and iron, and help the soil structure.

Horsetail (Equisetum)

Grows in low lime, sandy, light, acidic soil. Horsetail accumulates silicon, magnesium, calcium, iron and cobalt, which is released into the soil when it decomposes. Raising the pH and the fertility of the soil is the best way to eliminate horsetail from the garden.

Plantain (Plantago)
Thrives in heavy, compacted, acidic, low-fertility soil. Plantain is rich in calcium and magnesium. It also accumulates silicon, sulfur, manganese and iron. When turned under to decompose, it helps to deacidify the soil.




Quack Grass (Agropyron repens)
Grows in poorly drained, heavy clay soil or soil with a crusty surface. Quack grass has a net-like root system that can help control erosion on steep banks. It accumulates silicon, potassium and other minerals. Quack grass contains certain insecticidal properties that cause nerve damage to slugs. Some people use finely chopped quack grass as a mulch to repel slugs (with the caution that too much of the mulch could damage plantings).


Sorrel (Rumex)
Grows in acidic, low lime soil. Sheep sorrel can bring up calcium and phosphorus, minerals that alkalinize the soil. Turning sorrel under makes these minerals available in the soil.





Thistle
Thistle is found in heavy, compacted soil. It’s deep roots help break up the subsoil and bring up iron.






Vetch (Vicia)
Indicates low nitrogen, low fertility soil. A member of the legume family, vetch draws nitrogen from the air and fixes it in the soil as it decomposes. Vetches also accumulate potassium, phosphorus, copper and cobalt. Common vetch is sometimes used as a cover crop.




Resources on Weeds:

Weed Science Society of America Photo Gallery of Weeds

More Gardening Articles:
Saving Seeds, Sowing Food Security

Planning a Seed Saving Garden