Healthy soil is more than just the ground beneath us; it serves as a vital ecosystem supporting plants, animals, and people. According to Janice Mathews of UC Master Gardeners of Napa County, soil is composed of four main parts: about 25 percent air, 25 percent water, 45 percent minerals (including sand, silt, and clay), and roughly 5 percent organic matter, microbes, and humus.
This small fraction of organic material plays an important role in nutrient cycling and supports the diversity of microorganisms that live in soil. “There are more microorganisms in a spoonful of soil than there are people on earth,” Mathews stated. She noted that only about five percent of these organisms have been identified.
Mycorrhizal fungi help form soil aggregates by producing glomalin, a substance that binds soil particles together. This structure allows for better movement of air and water through the soil and aids in carbon sequestration. Plants interact with these microbes through photosynthesis, exchanging nutrients and contributing to climate change mitigation.
Mathews offered several recommendations for gardeners who want to maintain healthy soils:
– Minimize disturbance by avoiding tilling or breaking up clumps.
– Build organic matter by adding compost without digging it in.
– Leave roots from harvested crops in place to decompose naturally.
– Cover bare areas with mulch such as straw or leaves.
– Increase plant diversity above ground to promote diversity below.
– Rotate crops each season to reduce pathogens and nutrient depletion.
– Reduce energy use by choosing electric tools or hand tools when possible.
– Limit synthetic fertilizers, herbicides, and pesticides; use organics derived from natural sources instead.
Mathews cautioned against inorganic fertilizers because their production contributes to global warming and they do not improve long-term soil health. Inorganic pesticides can harm beneficial organisms as well as pets and people if used excessively.
She also stressed careful irrigation practices so that healthy soils can retain rainwater effectively while supporting productive gardens.
The UC Master Gardeners of Napa County will host two upcoming workshops: “Winter Rose Care” via Zoom on January 10 from 10 am to noon focusing on rose pruning techniques; registration is required for access details. Another session titled “Starting Your Own Vegetable Seedlings” will be held at the UC Cooperative Extension office at 1710 Soscol Avenue on January 10 from 2 pm to 4 pm. The workshop covers seed starting basics including moisture management, temperature control, lighting needs, seedling care until transplanting time—some materials will be provided but participants may bring their own seeds.
For gardening questions or issues, residents can contact the Master Gardener Help Desk online or visit the University of California Cooperative Extension Office during specified hours for assistance.
