Weeds are plants that grow where you don’t want them to. It is a label given with purely human whim that often interferes with nature taking care of its animals and soil. Unless you are removing invasive species, weeds have a purpose and can not only be useful medicinally, but also are indicator plants of how healthy your soil is.
In the February 1989 issue of Organic Gardening, I wrote an article called Selective Weeding. In it I described how weeds with deep tap roots not only break up the soil, but are nutrient ‘miners’; they take up minerals from down deep in the earth, send them up to their leaves, and then leave them on the soil surface when the leaves die, which improves the quality of the topsoil for other plants to thrive. Around here, wild radish is the most notable weed that does this although it is invasive, but it isn’t the only one.
Other weeds make good groundcover, such as purslane. Purslane needs fertile soil to thrive, so when you see it, you know there is good soil. It is also edible and a good source of calcium, iron and Omega-3 fatty acids…. a real plus for we vegetarians who don’t eat fish. Lamb’s quarters also grows in highly fertile ground and is very edible. Red clover also loves fertile soil and it’s importance to the pollinator insects is vital. Clover roots set nitrogen in the soil and is often used as a cover crop.
Plantain (Plantago major and not the banana) is naturalized throughout North America and I guarantee that everyone has seen it whether they know it or not. The variety with rounded leaves in a rosette is a common lawn weed, and the variety with long, lanceolet leaves with long veins that grows by waterways is much larger. Why streams and lawns? It thrives in soil that has low fertility and high ratio of water. Plantain makes an excellent salve for stinging nettle rash, insect stings and some say poison oak rash. If you brush against nettle while hiking you’ll know right away because it releases chemicals into your skin that burns for awhile and then dissipates. Look around for plantain, break a leaf and roll it between your fingers till it releases the juice and apply to the site.
Nettle is another great plant even though it stings in self-defense. The chemicals that sting are water-soluable, so if you pick young nettle and soak it or cook it like spinach, you have a green that is very high in Vitamin K, protein, calcium, maganese and potassium. Nettle soup is commonly served in other countries. Nettle is an indicator plant of soil that is high in nitrogen and phosphate, which explains why it often grows around abandoned buildings and farms where there has been animal and human waste. Nettle is the host plant for many butterfly species as well.
Poison oak has a place in our native forests as well. It is a plant which happens to give off a chemical that humans find irritating. It produces berries that birds rely on, it provides shade in the understory to hold in moisture and give safe harbor to many animals, it is beautiful with its bright green spring growth and dark red autumn shades. The entire plant produces an oil that gives most people a rash, which doesn’t begin to irritate the skin for several days. Thinking about the substance being an oil will help you consider how to deal with it. If you or your dog brush it, the oil will transfer to your clothes, skin or your dog’s fur (another great reason why you shouldn’t let your dog run off-leash in natural areas!), and transfer again when it is touched. If burned, the toxicity is increased and you can inhale the fumes and become critically ill. If you think that you’ve brushed against poison oak, wash your clothes separately from the rest of the laundry and wash your skin well. There are many products on the market which help dissolve the oil, such as Technu, which is a wash for just after you’ve touched the plant. On hot days the plant’s oils carry in the air so people who are very sensitive should avoid poison oak habitat in the summer.
Weeds that indicate compacted soil, which is low in oxygen, are bindweed (looks like a small white or pink morning glory), quackgrass and chicory with its tall blue flower. Chicory’s deep taproot mines the minerals and breaks up the soil, and bindweed covers the soil providing some shade and protection against more compaction and dropping leaves over an extended area for mulch. Quackgrass secretes a chemical that supresses other plant growth as it travels via rhizome, breaking up the soil surface and carpeting it for protection.
Dandelions, a weed of childhood fantasy, of back-country wine, of spring tonic greens, are happy little plants that lawn owners ruthlessly kill. They grow in many soils, but are indicators of acidic soil. Henbane is a sign of alkaline soil.
Whether you keep your weeds, selectively weed, or eradicate them all, you should at least learn what they have to tell you. A good list of California weeds is at http://www.ipm.ucdavis.edu/PMG/weeds_intro.html .. An extremely valuable book that I have used so often when conducting hikes (and there is always a little girl that asks what every little plant is along the way), is Roadside Plants of Southern California by Thomas Belzer. It has photographs, descriptions and whether the plant is native or not. Another book is the Natural History of Vacant Lots by Matthew Vessel et al. These are wonderful guides for all the plants that fall between the cracks of most plant ID guides.
Just remember that plants communicate to you, and each have a purpose to fulfill. Whether it be as a mineral miner, a canopy or shade plant, a pollinator and food source, a nitrogen-fixer, a soil breaker, a mulch plant, each is doing something to help build earth fertility. Plants that are non-native take the place of the ones that are native and important to an area and its habitat, supplanting perhaps a plant that is the host for a particular butterfly. Be enlightened when doing yardwork. Feel free, though, to eradicate any Bermuda grass that you see, because it is a weed against which I have a personal vendetta! Happy gardening.