The underground network: Fungi, Roots, and What Really Connects Your Garden

Beneath every healthy garden runs a partnership much older than trees themselves - something I only discovered when I fell hopelessly in love with Merlin Sheldrake and his book 'Entangled'.

Thread-like fungi wrap around and into plant roots, reaching out through the soil in a filigree far finer than any root could manage, and strike a deal that has shaped life on land for something like 400 million years. It's one of the most important relationships in your garden, and, thanks to a decade of viral storytelling, also one of the most misunderstood.

So let's do both halves justice: the genuinely astonishing science that is beyond doubt, and the popular "trees talking to each other" story that has raced some way ahead of the evidence.

The deal beneath your feet

Mycorrhiza simply means "fungus-root." The fungi colonise a plant's roots and extend their own microscopic threads or 'hyphae' out into the soil. Those hyphae act as a vastly extended root system, foraging for water and nutrients (phosphorus above all, but also nitrogen and trace elements) in pores far too small for a root hair to enter. In return, the plant pays in sugars made by photosynthesis. It's a trade: the plant gets reach, the fungus gets fuel. Around 72% of the world's plant species form these partnerships, so the odds are that almost everything in your borders is quietly doing it right now.

There are two main types worth knowing, because they change how you plant and care for a garden:

Arbuscular mycorrhizal fungi (AMF) partner with the great majority of garden plants - vegetables, grasses, perennials, most flowers, and many shrubs. These are the workhorses of a border.

Ectomycorrhizal fungi (EcM) partner mainly with trees, including many of the natives you might plant for a wilder garden, such as oak, birch, beech, hazel, and pine. If you've ever seen toadstools flushing around the base of a birch, you've seen this partnership fruiting.

Why the fungi matter and how they tie back to water

The benefits to your plants are well established and considerable. Mycorrhizal plants take up nutrients more efficiently, cope better with drought, and show greater resistance to root pathogens and pests. By intercepting nutrients before they wash away, the fungi even reduce the leaching of nitrogen out of the soil.

But there's a benefit that connects directly to soil's ability to hold water, the subject of the last article in this series. Arbuscular mycorrhizal fungi secrete a sticky, glue-like glycoprotein called glomalin (soil scientists, being cautious, tend to call what they

actually measure glomalin-related soil protein, or GRSP). This substance binds fine soil particles into crumbs and aggregates, and it's precisely those aggregates that create the pore spaces where water infiltrates and is held. So the fungal network isn't just feeding your plants; it's quietly building the very structure that lets your soil act as a sponge. Fungi and organic matter are two ends of the same story.

The bit everyone's heard, and the bit they haven't

Here's where the roots really do connect. Because a single fungus can colonise more than one plant at once, the roots of neighbouring plants and neighbouring trees can be physically linked underground through a shared fungal partner. Scientists call these common mycorrhizal networks (CMNs); the press christened them the "wood wide web." Landmark experiments, beginning with Simard and colleagues in 1997, showed that carbon can travel from one tree to another through such a network. That much is real, and remarkable.

From there, though, the popular story took off faster than the science could follow. You've likely heard the claims: that forests are woven into cooperative superorganisms; that wise "mother trees" recognise their own seedlings and deliberately funnel food and warnings to them through the network. It's a beautiful narrative, and, according to a growing body of scientists, it's well ahead of the evidence.

In 2023, ecologists Justine Karst, Melanie Jones, and Jason Hoeksema published a careful review in Nature Ecology & Evolution examining the three most repeated claims. Their findings were sobering. Common mycorrhizal networks have really only been mapped in two forest types, the Douglas fir in British Columbia and a pine species in Japan so we can't yet say they're widespread. There is no strong evidence that these networks reliably benefit seedlings in the wild. And the "mother tree" idea of trees preferentially nurturing kin rests on very thin support. Most strikingly, when the authors traced how older studies were cited, they found the science drifting: among papers published in 2022, fewer than half of the statements made about the original field studies were accurate. The story had, in effect, been embellished with each retelling.

This doesn't mean the network is a myth. Networks demonstrably exist, and carbon can move across them. Other researchers, publishing in the same period under the pointed title "Facts, not fantasy," defend that transfer as real and ecologically meaningful. Curious plants called mycoheterotrophs - think of the ghostly bird's-nest orchid, which has no green leaves at all - survive entirely by drawing carbon from trees through shared fungi, which is living proof these networks can move resources. The honest position is that the plumbing is real, but what flows through it, how often, how far, and in whose interest - the plant's, or the fungus's own - remains genuinely unsettled. It may be less a benevolent forest internet and more a marketplace, with the fungi trading shrewdly on their own account.

What this means for your garden

You don't need a woodland to benefit from any of this. The same fungi are working (or waiting to work) in your garden beds right now. The way to help them is, once again, the way of the rewilder: less interference, more life.

Dig as little as possible. Most mycorrhizal material lives in the top 10–15cm of soil, and turning it over shreds the very threads you want to keep. Some studies suggest conventional tilling can cut fungal diversity substantially. No-dig methods like lasagne beds, forest gardening and mulching let the network build and persist. So mulch, don't bury. Feed the soil from the top with compost and leaf mould. A varied litter of leaves and debris above ground supports a richer fungal community below.

Ease off the fungicides AND the soluble feed. Fungicides harm the good fungi along with the bad - its like antibiotics - they wipe out all bacteria in our gut not just the bad kinds. And heavy, quick-release phosphate fertilisers actually suppress mycorrhizal partnerships: when a plant can get phosphorus for free, it stops paying the fungus for it, and the relationship withers.

Plant diversity, and keep living roots in the ground. Different plants and continuous root activity feed and sustain the fungal community year-round. Bare, fallow soil starves it.

Be sceptical of shop-bought inoculants. In healthy garden soil the fungi are already present, and you're almost always better off encouraging your native populations than buying in spores, many of which are the wrong species for your plants anyway. Save your money for compost.

The quiet part

What connects a garden isn't a tidy web of cooperation with a purpose we can flatter ourselves by recognising. It's something stranger and older: a sprawling, self-interested, endlessly negotiated partnership between plants and fungi, most of it invisible, that happens to build fertile, water-holding, living soil as a by-product. Tend it lightly; dig less, mulch more, let the roots and the fungi get on with their bargaining and you become, in the best sense, a modern day enabler to a deal that was struck long before there were gardeners to admire it.

References & further reading

Karst, J., Jones, M.D. & Hoeksema, J.D. (2023). "Positive citation bias and overinterpreted results lead to misinformation about common mycorrhizal networks in forests." Nature Ecology & Evolution, 7, 501–511.

Simard, S.W. et al. (1997). "Net transfer of carbon between ectomycorrhizal tree species in the field." Nature, 388, 579–582.

Rog, I., Klein, T., van der Heijden, M.G.A. et al. (2023). "Belowground carbon transfer across mycorrhizal networks among trees: Facts, not fantasy." Open Research Europe, 3.

Gerz, M., van der Heijden, M.G.A. et al. (2024). Work on mycoheterotrophic plants as natural evidence of carbon transfer through common mycorrhizal networks. Nature Plants.

Smith, S.E. & Read, D.J. (2008). Mycorrhizal Symbiosis, 3rd edn. Academic Press — the standard reference text.

University of Florida IFAS Extension (PP383). Biology, Ecology, and Benefits of Arbuscular Mycorrhizal Fungi in Agricultural Ecosystems — on nutrient uptake and glomalin.

Society for the Protection of Underground Networks (SPUN). How to Encourage Healthy Mycorrhizal Networks in Your Own Soil.

Compost Magazine. Mycorrhizal Fungi: The Underground Network That Feeds Your Plants (drawing on Gosling et al., 2006) — practical garden guidance and the case for encouraging fungi over inoculating.