Why is soil sometimes described as healthy?
And what are those cute purple flowers?
Q: I’ve heard the expression “soil health,” but I don’t understand why we consider soil healthy or unhealthy. It always seems to grow something! Why is it important?
A: Good soil health is the foundation for growing healthy plants. Soil growing just anything isn’t ideal, either in gardens or in natural areas (which should be populated with native plants). There are certainly plants well-adapted to dealing with soil that gardeners would consider horrible, but they tend to be rare specialists or species so aggressive and adaptable that they skew invasive.
The former aren’t typical garden plants and the latter we definitely don’t want to encourage.
We say soil has “health” because it’s composed of an incredible number of living things in addition to the rocky minerals it originally eroded from. The abundance and diversity of these organisms forms the foundation for soil health. Organic matter in the soil comes from the breakdown of dead plants and animals; it’s the main food of the microbe population, which itself forms the vast bulk of the types of soil life. Without magnification, we can only see a tiny fraction of what’s living in the soil, so it’s easy to forget just how important they are as a group.
It might be easier to conceptualize using parallels with human gut microbes. They help us digest food and extract nutrients; soil
microbes digest organic matter into plant-useful nutrients, plus help plants absorb those nutrients and moisture. Our gut microbes can be thrown out of balance or repressed by medication; in soils, by pesticides and excessive fertilization. In some cases, gut microbes might protect us from certain diseases or disorders; in soils, some colonize plant roots and prevent infectious, disease-causing microbes from gaining access. Lastly, conditions in our gut promote or suppress certain species, as do soil conditions like pH and oxygenation.
We tend to forget about our body’s microbe partners too until
something upsets the balance. In both gardens and wild areas, we upset the microbial balance by degrading habitat: compacting the soil, making drastic changes to soil chemistry (pH, nutrient levels), changing water flow, or introducing invasive species.
One important benefit of these life forms that contributes to healthy soil is their ability to improve soil texture. Their secretions glue fine soil particles together into larger clumps, which not only lessens erosion risk but also improves aeration and water retention. Both roots and these organisms need this air and water access to stay healthy, and disturbances (like from tilling) can damage soil structure and undo this progress. Microbes that thrive on limited oxygen tend to be those we don’t want — pathogens like root rot.
Soils in areas with human development may not ever be as healthy as they were before we altered the landscape. We can, though, improve soil’s health by practicing sustainable gardening techniques and viewing soil not as an inanimate substance we dig in but as a living, nurturing environment for our plants.
Q: I see short pinkish-purple flowers popping-up everywhere in the grass around the neighborhood, especially in common areas and hellstrips. Are they wildflowers or weeds? A:
Given the time of year, location, and abundance in disturbed environments, the two likely candidates for what you’re seeing are purple deadnettle (lamium purpureum) and henbit (lamium amplexicaule). I admit they can be cute and pretty — just about any cheerful flowers in early spring are welcome — but they’re weeds and not native. At least they’re more of a naturalized nuisance than an invasive menace.
Although they can add spring pollinator resources to an otherwise monotonous lawn, if a gardener wants to let “weeds” pepper their turf, native alternatives include wild violets, spring beauty, pussytoes, and star chickweed. (Note that most chickweeds found in a lawn are non-natives.)
Both of these plants are winter annuals, so will die off on their own by summer. For areas where you want to manage them, preventive efforts begin in autumn, since they germinate as the weather cools. The only herbicide-free approach is to pull or mow the ones you see already growing and to keep the next generation’s seeds from germinating by maintaining stiff competition via good turf health and vigor or by crowding them out with other noninvasive ground covers.