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How Photosynthesis Feeds the Soil

ByStephen Albert

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Healthy soil begins with sunlight. Every green leaf in your garden acts as a tiny solar panel, capturing light energy and transforming it into food—not only for plants but for the soil life beneath them. Over decades of growing vegetables year-round in Sonoma Valley, I’ve seen how living roots sustain soil fertility long after harvest. Photosynthesis is the engine that drives that process.

This post is part of my Regenerative Gardening series. You can also read:

🌱 1. The Photosynthesis Equation: Sunlight to Sugars

Photosynthesis converts sunlight, water, and carbon dioxide into simple sugars (carbohydrates) and oxygen:

Sunlight + CO₂ + H₂O → Sugars + O₂

These sugars serve as energy for plant growth. But in a living soil system, a remarkable thing happens—plants share much of that energy with the organisms around their roots.

🌾 2. Root Exudates: The Energy Exchange Below Ground

Up to 40 percent of a plant’s photosynthetic energy flows underground as root exudates—liquid carbon compounds like sugars, amino acids, and organic acids.

In the rhizosphere, the narrow zone around plant roots:

  • Bacteria and fungi feed on these exudates and multiply.
  • Protozoa and nematodes consume the microbes, releasing nutrients in plant-available forms.
  • Mycorrhizal fungi exchange minerals and water for carbon sugars.

This constant flow of carbon fuels the soil food web, creating a dynamic partnership between plants and soil life.

🪱 3. Photosynthesis Builds Soil Carbon

Through photosynthesis, plants draw carbon from the atmosphere and channel it underground. When soil microbes process root exudates and die, their remains form stable organic matter—humus.

This process, known as carbon sequestration, enhances soil fertility, structure, and water retention. In regenerative gardening, it’s the foundation for long-term resilience.

Each living root acts as a carbon pipeline, transferring solar energy into the soil.

🍃 4. Keeping Photosynthesis Active Year-Round

To keep the soil food web alive and thriving, maintain photosynthesis as much of the year as possible.

Regenerative practices that support continuous photosynthesis:

  • Keep living roots in the soil: Grow cover crops or winter vegetables.
  • Avoid bare soil: Cover with mulch or living groundcovers.
  • Plant diverse crops: Different plants feed different microbes.
  • Reduce tillage: Preserve root channels and fungal networks.

In Sonoma Valley’s mild Zone 9b climate, cool-season crops like kale, fava beans, and peas can photosynthesize all winter, keeping soil microbes active and well-fed.

🌍 5. The Gardener’s Role in the Carbon Cycle

Every gardener is part of the planet’s carbon cycle. When you plant, you capture sunlight; when you compost, you recycle it; when you maintain living roots, you store it in the soil.

Photosynthesis doesn’t just grow plants—it regenerates the earth beneath your feet. By keeping soil covered and alive, you’re harnessing the sun’s energy to feed an underground ecosystem that will repay you with fertility, resilience, and abundance.

🌿 Next in the Regenerative Gardening Series

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Stephen Albert is a horticulturist, master gardener, and certified nurseryman who has taught at the University of California for more than 25 years. He holds graduate degrees from the University of California and the University of Iowa. His books include Vegetable Garden Grower’s Guide, Vegetable Garden Almanac & Planner, Tomato Grower’s Answer Book, and Kitchen Garden Grower’s Guide. His Vegetable Garden Grower’s Masterclass is available online. Harvesttotable.com has more than 10 million visitors each year.

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