Fungi in Soil: How They Support Living Soil
Fungi are among the key organisms at work in soil and compost. Alongside bacteria and other decomposers, they help break down plant material, interact with roots and feed the wider soil food web. Understanding fungi in soil helps explain why a healthy growing medium is more than a place for roots to sit.
Fungi help break down complex organic matter
Fungal threads, called hyphae, grow through soil and decomposing material. Many fungi release enzymes that help break down tough plant compounds, including lignin in wood. Bacteria and other organisms also contribute to decomposition, and the mix of organisms changes as material breaks down.
As organic matter is transformed, nutrients are released and recycled through the soil food web. Fungal growth and the residues left as it turns over can also contribute to soil organic matter. If you see mushrooms or other fungal fruiting bodies on a decomposing stem or wood chip, you are seeing one visible part of a much larger organism; most of its growth is usually the fine mycelium within the material.
Some fungi form partnerships with plant roots
Mycorrhizal fungi can form a close association with the roots of many plants. The plant supplies the fungus with carbon produced through photosynthesis. In return, the fungal hyphae can explore soil beyond the immediate root surface and help the plant access nutrients such as phosphorus, as well as water.
The benefits depend on the plant, fungal species and growing conditions. Not every fungus forms a mycorrhizal partnership, and a living soil system contains many kinds of fungi with different roles.
Fungi can contribute to plant protection
Some fungi and mycorrhizal partnerships can help reduce pressure from certain soil-borne pathogens. Depending on the organisms and conditions, this may involve competing for space or resources, producing compounds that affect other microbes, forming a barrier around roots, or influencing the plant’s own defences. These effects are specific and variable, so fungi should be seen as part of a wider, balanced growing system rather than a guaranteed shield against pests or disease.
Fungi are part of the soil food web
Fungi are not only decomposers or partners to plants; they are also food for other organisms. Some nematodes and small soil animals graze on fungal hyphae. As they feed and release waste, nutrients held in microbial biomass can return to the soil in forms that may become available to plants and other organisms.
These feeding relationships help move energy and nutrients through the soil food web. They also help keep populations in balance, although the outcome depends on which organisms are present and the conditions in the soil.
Why fungi matter in living soil
In living soil, fungi work alongside bacteria, roots and soil fauna to transform organic matter, move nutrients and support a functioning soil community. Their presence is one reason a biologically active growing medium behaves differently from an inert substrate, but plant health still depends on the whole system: suitable structure, moisture, air, nutrients and good growing practice.
Our peat-free Living Soil Potting Mix is made with mature, hand-made compost and selected ingredients. Explore the mix if you are looking for a ready-to-use growing medium for containers, raised beds or larger growing areas.
Further reading
For readers who want to explore fungi and soil biology further: Mycelium Running; Teaming with Fungi; and Regenerative Soil.
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