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Learn how healthy food grows.

Plain-language guides to the living world under your garden, plus workshops, resources and member events.

Illustration of a workshop table with seedling pots, a hand lens, seed packets and a clipboard

Understanding the soil food web

Five groups of life that feed your plants.

Plants feed the soil with sugars from their roots. In return, an underground community of organisms feeds, protects and waters them.

Illustration of a petri dish seen from above with four quadrants of colonies

Bacteria

The smallest and most numerous. They break down simple compounds, cycle nutrients like nitrogen and help glue soil into crumbs. Actinobacteria are a specialist group that tackle tougher material and give healthy soil its earthy smell.

Decorative soil mound with a green sprout

Fruit tree over layered garden beds with roots

Fungi

Threads called hyphae weave through soil. Some break down tough woody material. Others partner with plant roots, reaching water and nutrients the roots cannot, and trading for sugars the plant makes in sunlight.

Protozoa

Single-celled hunters that feed on bacteria. When they eat, they release nutrients in forms plants can take up, right next to the roots.

Nematodes

Microscopic roundworms. Many feed on bacteria or fungi, some eat other nematodes and protozoa, and a few feed on roots. A healthy mix keeps the troublemakers in check.

Oomycetes

Fungus-like organisms, often called water molds. Some cause damping off and root rots. They tend to thrive in waterlogged, compacted soil, which makes them a useful warning sign.

Why it matters

More than half of Earth's species live in soil.

A 2023 review in PNAS estimated that about 59 percent of species on Earth live in soil. A single handful of healthy soil holds more microbes than there are people on the planet.

Fungi extend far beyond what roots could reach alone. Research by Suzanne Simard and others suggests these fungal networks can carry resources and signals between plants and trees.

Test your own soil