It’s easy to take soil for granted, but the stuff we call “dirt” is actually a very complex ecosystem that is essential for most life processes. Like the rest of the earth, soil has become degraded by our modern industrial society. Plants grown in poor, compacted soil that is low in nutrients are likely to be weak, easily stressed, and consequently, targets for insects and disease. In contrast, soil that drains well, teems with life, and is uneroded and minimally tilled will give plants a much better chance at a healthy, productive life. A foundation of healthy soil is the key to healthy root systems and a beautiful garden.
Quality soil is a varied mix of rock particles, water, air, and organic matter that hosts countless interrelated organisms. Some are visible, like worms and beetles, but most are not, like the diverse population of fungi, bacteria, and other microbes. These organisms, along with the organic matter that sustains them, are critical to the long-term productiveness of the soil, so protecting and nurturing them is crucial.
The single most important thing you can do to increase soil health is to add soil conditioners that contain organic matter (OM). OM is made up of living creatures, their
waste, and decaying parts of dead plants and animals of the soil food web that recycle nutrients into the soil. OM has many functions. It improves soil stucture and aeration by making it more granular, thereby increasing its ability to absorb and release both air and water via channels. Soil that’s loose and crumbly is much less prone to runoff, erosion, and nutrient loss than soil that is hard and compacted. Another benefit is a slightly warmer soil earlier in the year, allowing for earlier planting of spring vegetables.
OM also ensures a continual food supply for the myriad soil microbes that convert organic elements like nitrogen into inorganic forms that plants can use. The decomposition process improves soil structure with the help of fungi’s threadlike filaments and carbon-rich exudates that join soil particles together to form small groups or aggregates. These aggregates aid in root development because they keep carbon and minerals accessible at the root zone. Carbon also holds water near the roots where it is accessible between waterings. Thus, OM shields crops from drought, as well as nutrient stress. Although it’s generally not high in nutrients, it is greatly superior to synthetic fertilizers which offer only blasts of chemicals (sometimes more than a plant can use) and consequent pollution of ground water. Moreover, research argues that the net effect of synthetic nitrogen use may actually reduce soil’s OM content.
Knowing your soil’s makeup is helpful, but even challenging soils – like clay – can be transformed into relatively fertile soil by careful cultivation and regular addition of organic matter. All soil types – sand, silt, clay, and loam – benefit from added OM. In sandy soils, it protects plants against drought, and in clay soils it helps increase air spaces within the soil, thereby creating better drainage. Loam is what gardeners strive for–a balance of sand, silt, clay, and decomposed OM, somewhat like an undisturbed forest floor where soil organisms are very active. Loam is dark, easily crumbled, pH neutral, and packed with life.
Because decomposition continually changes OM into inorganic nutrients that can be utilized by growing plants, it should be added to the soil on a regular basis when growing edibles. How much should you add depends on your soil and the plants that may already be growing in it. In general, if you are starting with soil that’s been growing lawn, incorporate at least three inches. If you are trying to revive lifeless soil that’s been under something impermeable, like concrete, add much more. The more OM you supply, the livelier the soil creatures are likely to be and the more intense the competition between beneficial soil microorganisms and plant pathogens–in other words, OM creates a stronger balance between the good guys and the shady characters lurking about.
For established veggie gardens and parts of your yard that grow native species or ornamentals, simply applying it as a mulch works well and causes the least disturbance to soil inhabitants. Apply a couple of inches of weed-free compost, such as leaf compost, after planting in spring or fall. Be certain to keep it at least several inches away from tree and shrub trunks to prevent bark rot, and off of perennial crowns and ground cover. For established gardens, don’t get into the habit of applying mulch every year—it can be too much of a good thing. Applying mulch right after planting is great, but continual thick layers can be detrimental. Nature’s mulch, fallen leaves, will protect the soil, give places for overwintering insects to sleep, and provide food for animals like birds.
To further protect soil, minimize tillage and any activities that destroy soil structure (break or crush aggregates), like working (or even walking on) the soil when it’s wet. If you need to mess with your soil in springtime, check to see if the soil’s workable by digging up a ball of soil about six inches down. Toss the ball six inches in the air—if it crumbles when it hits hard ground, it’s ready to work. If not, wait until it warms/dries further.
One drawback to mulch: Seventy percent of native bees nest in the ground. They require bare soil in which to raise their young, so don’t cover every square inch of your yard! Pollinators desperately need habitat.
– Eileen Stark BACK to Articles