The Market Under Your Feet

Turn over a clump of healthy soil, or lift a log that has sat on the ground for a season, and you will often find fine white threads running through it. Most people brush them off as mould. They are the visible edge of mycelium, the body of a fungus, and they belong to the oldest working network on the planet.

It has been running for more than 400 million years. It trades, keeps score, builds redundancy and prunes what doesn’t pay. It also has a hype problem. Let’s take all of it in turn.

The mushroom is the least of it

A mushroom is to a fungus what an apple is to a tree: the fruit, not the organism. The organism is the mycelium, a mesh of threads called hyphae, each finer than a human hair, growing through soil, wood and roots. Most of a fungus lives where you will never see it.

The scale can be absurd. In Oregon’s Malheur National Forest, a single honey fungus, Armillaria ostoyae, has been mapped across roughly 965 hectares of forest floor and is estimated to be thousands of years old. Above ground you would notice a few clumps of mushrooms and some dying trees. Below ground, it is genetically one individual.

A market with 400 million years of price discovery

Most of the plants you grow have a business partner underground. Only around 8% of vascular plant species never form a mycorrhizal partnership (mycorrhiza literally means fungus-root). The large majority trade.

The deal is simple. Fungal threads reach far beyond the roots, gathering water and nutrients, especially phosphorus, and deliver them to the plant. The plant pays in carbon: sugars and fats made from sunlight.

And it isn’t charity. In a 2011 study published in Science, researchers showed that both sides reward the better partner. Plants sent more carbon to the fungi that delivered more phosphorus, and fungi sent more nutrients to the roots that supplied more carbon. Cooperation, kept honest by keeping score. Fossils from the Rhynie chert in Scotland show this partnership inside some of the earliest land plants, more than 400 million years ago.

The volume is staggering. A 2023 review estimated that land plants send about 13 billion tonnes of CO₂-equivalent a year into mycorrhizal fungi, at least temporarily. That is roughly 36% of the world’s annual fossil fuel emissions. This is not a side deal. It is one of the largest flows of value on the planet.

Built the way an engineer would build it

Researchers in the UK tracked how a woodland fungus, Phanerochaete velutina, builds its network as it forages (this one is a wood decayer, not a root partner, but it runs the same kind of mycelium). The pattern was striking. It over-produces connections while exploring, then thickens the links that carry the most and recycles the rest. The finished network balanced transport efficiency, cost and resilience to damage, the same trade-offs engineers fight over when they design transport systems.

Read that pattern again: explore widely, reinforce what carries value, cut what doesn’t, and keep a few spare links so one cut never severs everything. That is the playbook for a resilient supply chain, a portfolio and a peer-to-peer network. It is also exactly what we wrote about in our last post, Not Your Keys, Not Your Audience: never build on a single point of failure.

Where the story gets oversold

You may have heard that the forest is a “wood wide web”, where mother trees feed their seedlings and trees warn each other of danger through fungal cables. It is a beautiful story. The evidence is thinner than the story.

In 2023, three forest scientists went back through the research behind the most popular claims: that these networks are widespread in forests, that they move resources that help seedlings, and that mature trees preferentially send resources and warnings to their offspring. They concluded the popular versions had run well ahead of the evidence, and they found unsupported claims being repeated more and more often in the scientific literature itself.

None of that makes mycelium less remarkable. The trade is real. The networks are real. The carbon flows are real. What is shaky is the leap to trees as a caring family with a messaging app. Data over narratives: the true version is astonishing enough.

What it means in your garden

Spring is here in Australia, so if you are planting out beds right now, these are the habits that keep the underground market open for business.

• Dig less. Tilling physically tears the hyphal networks apart. Top-dress with compost and let the worms and fungi do the mixing.
• Go easy on phosphorus. When phosphate is abundant, plants largely stop investing in their fungal partners. Heavy, high-P fertiliser effectively shuts the market down.
• Keep living roots in the ground. The fungi need a plant to trade with. Perennials, cover crops and not leaving beds bare keep the partnership running between seasons.
• Mulch, and leave some wood. Wood-decaying fungi break down woody material and return its nutrients to the soil. A little decaying wood on the edge of a bed is food for the network.
• Protect before you buy. Before spending money on a bag of fungal spores, protect the network that is almost certainly already living in your soil.

The law underneath

Strip away the biology and mycelium runs on rules any market or network would recognise. Trade value both ways. Reward the partners who deliver. Reinforce the links that carry the most, prune the ones that don’t, and never let one cut sever everything. No central server, no single point of failure, and four hundred million years without going offline.

That is the network we are trying to build here.

Have you noticed white threads in your compost or under the mulch? And are you a digger or a no-dig convert? Hit reply and tell us.

Grown with intention by Dynamic Nexus Garden.