The Underground World We Were Never Taught to See
Most gardeners have been taught to look at a plant from the soil line upwards.
Are the leaves green? Is it flowering? Does it need fertiliser? Does it need more water?
But some of the most important activity in the life of a plant is taking place in a layer only millimetres thick around its roots. It is not simply “soil”.
It is an extraordinary living interface built from substances released by the plant, bacteria and fungi living around the root, microscopic gels, water, minerals, root hairs, soil particles and chemical signals.
Scientists divide this underground world into several overlapping zones: the rhizosphere, rhizoplane, mucilage or mucigel, microbial biofilm and, in many plants, the rhizosheath.
Together they change the way we should think about feeding plants. Because roots are not merely straws sucking nutrients from dirt. They are participants in a living biological system.
First: what is the rhizosphere?
The rhizosphere is the narrow region of soil directly influenced by a living root.
It is one of the most biologically active places in soil.
Plant roots release carbon compounds into this zone, including sugars, amino acids, organic acids and many other compounds. These root deposits and exudates provide food and signals that influence the microorganisms living nearby.
This creates what scientists call the rhizosphere effect: microbial populations and microbial activity close to a root can be dramatically different from those in the bulk soil only a short distance away.
Research using carbon tracing has put the actively influenced rhizosphere on the scale of only a few millimetres in some systems.
Tiny in distance. Enormous in consequence.
The plant is therefore not simply encountering whatever happens to be in the soil. Through its roots it changes the environment around itself and influences which organisms can flourish there.
Different plants create different rhizospheres. Plant species, genetics, age, health, soil conditions, moisture and nutrient status can all alter the compounds released by roots and therefore the community that develops around them.
Then there is the rhizoplane
Move closer again.
The rhizoplane is essentially the root surface itself and the soil particles and microorganisms immediately adhering to it. This is prime biological real estate.
Microbes do not necessarily live around roots as isolated organisms swimming independently through soil water. Many attach themselves to surfaces. And once attached, microorganisms can form colonies and communities. Which brings us to one of the most interesting parts of the story.
The root can be surrounded by a living biofilm
The word biofilm is often associated with bacteria growing on wet surfaces. But biofilms are also important around plant roots. A biofilm is a community of microorganisms living together within a self-produced matrix of substances known broadly as extracellular polymeric substances, or EPS.
Think less of loose bacteria floating around individually and more of a microscopic living community embedded within a hydrated gel.
EPS can contain polysaccharides, proteins, extracellular DNA and other compounds.
The matrix helps microbes attach to surfaces and to one another. It can retain moisture and nutrients, provide some protection from environmental stresses and create microscopic habitats in which organisms interact.
Biofilm formation by plant-associated bacteria has been documented for decades. Microbial colonies embedded in mucilage around roots were reported as far back as the 1970s, and subsequent research has strengthened the connection between root colonisation and biofilm formation.
But there is another remarkable part of the system. The microbes are not making all of the gel themselves. The plant is making some of it.
Plants manufacture their own root gel
Growing roots release a gelatinous substance called mucilage. It is rich in complex carbohydrates, particularly polysaccharides, along with proteins, minerals, lipids and other compounds.
Research describes mucilage production as occurring in almost all plants. Mucilage is particularly associated with the root cap and growing root tip, although its effects remain within the surrounding root environment.
Why would a plant spend valuable carbon making slime underground? Because that slime is extremely useful.
Root mucilage can:
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lubricate a growing root as it pushes through soil;
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help retain water near the root;
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maintain physical contact between soil and root;
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influence movement of water through the root–soil interface;
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bind soil particles;
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affect soil aggregation;
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interact with nutrient ions;
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provide carbon and nutrients for microorganisms;
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and create habitat for microbial communities.
One review of mucilage composition reported approximately 78% polysaccharides, with smaller proportions of proteins, minerals and lipids.
Those polysaccharides have particularly interesting properties. They can absorb water, adhere to soil surfaces, participate in ion exchange and provide energy for microorganisms. And this is where recent research becomes fascinating.
The plant may actually help provide the architecture for the microbial biofilm
A 2022 paper titled “Biogels in Soils: Plant Mucilage as a Biofilm Matrix That Shapes the Rhizosphere Microbial Habitat” proposed that we should stop viewing root mucilage simply as plant slime.
The researchers compared plant mucilage with microbial EPS and found important similarities in their physical and chemical characteristics.
Their proposition was striking:
plant mucilage may function as part of the biofilm matrix in which rhizosphere microorganisms live.
In other words, the plant may help construct the habitat occupied by its microbial community.
The authors describe mucilage as potentially creating a protected, hydrated environment conducive to nutrient mobilisation and intense microbial activity.
That completely changes the picture of a root.
Instead of:
ROOT → SOIL → FERTILISER
we begin to see:
PLANT → ROOT EXUDATES + MUCILAGE → MICROBIAL COMMUNITY → NUTRIENT CYCLING + WATER RELATIONSHIPS + SOIL STRUCTURE → PLANT
It is a biological exchange system.
And then soil can become attached to the whole structure
Sometimes the interaction becomes physically obvious. Pull certain healthy plants carefully from soil and you may notice soil remaining firmly attached around fine roots rather than simply falling away.
That tightly bound soil is called the rhizosheath. A rhizosheath is different from the broader rhizosphere. The rhizosphere is all the soil significantly influenced by the root. The rhizosheath is the cohesive layer of soil actually adhering to the root system.
Its development involves a combination of factors, particularly:
root hairs + plant mucilage + microorganisms + microbial polymers + soil properties + water.
Research shows rhizosheath soils can have markedly different physical, chemical and biological properties from surrounding soil.
A major 2023 systematic review and meta-analysis reported, across the studies examined, higher water content, organic carbon, water-extractable organic carbon and microbial biomass nitrogen in rhizosheath soil compared with other rhizosphere counterparts.
The authors describe the rhizosheath as having important roles in soil aggregation, water and nutrient acquisition, carbon cycling and microbial colonisation.
That “dirty root” may therefore be telling us something very important. The soil stuck to a living root isn't necessarily dirt that failed to shake off. It can be a constructed biological habitat.
The network extends beyond the film
Then fungi enter the story. Fungal hyphae can grow through spaces far smaller than plant roots can occupy. Mycorrhizal fungi associated with plant roots can extend hyphal networks from roots into surrounding soil, effectively expanding the volume of soil explored by the plant–microbial system.
Bacteria and fungi should therefore not always be thought of as separate actors. Research increasingly describes interactions involving plants, fungi and bacteria together.
Fungal surfaces themselves can provide habitat for bacterial communities, while bacteria can influence fungal behaviour and nutrient processes.
The underground system is consequently more complex than the popular picture of a plant connected to a single fungus.
It is a network of:
roots, root hairs, exudates, mucilage, bacteria, fungi, microbial metabolites, soil particles, water, gases and minerals.
And it changes continually.
Is this only found in tropical plants? No.
This is an important distinction. Our original interest came from looking at biology around the root zones of plants, including tropical plants. But the underlying phenomena are far broader.
Scientific literature describes root mucilage as being produced by almost all plants. Bacterial colonisation and biofilm formation occur across a very wide range of plant species.
The rhizosphere exists wherever living roots influence the soil around them.
Rhizosheaths are also widespread among flowering plants, although they are not equally developed in every species. They are particularly prominent in some grasses and plants adapted to environments where maintaining root–soil contact, water and nutrient access is advantageous.
So we should not say:
“Every plant forms exactly the same film or sheath.”
It doesn't. We can say:
Plants across the plant kingdom create biologically active root interfaces involving exudates, mucilage and microorganisms, but the structure and intensity of those systems vary enormously between plants and environments.
That distinction matters.
Roots feed their microbial workforce
One of the ideas gardeners often find surprising is that plants deliberately lose some of the carbon they have worked hard to produce through photosynthesis.
Leaves capture carbon dioxide. Through photosynthesis the plant converts that carbon into energy-rich compounds. Some of that carbon goes below ground.
Roots release sugars, organic acids, amino acids and other compounds into the surrounding environment. Why? Because carbon below ground is not necessarily waste. It can be investment.
Root-derived carbon helps support microbial populations. Those organisms can in turn participate in processes including:
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decomposition and nutrient cycling;
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conversion of nutrients into different chemical forms;
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phosphorus mobilisation;
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nitrogen cycling;
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formation of soil aggregates;
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production of extracellular polymers;
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interactions with plant hormones;
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competition with other microorganisms;
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and modification of the physical environment surrounding roots.
Not every microorganism does every job. Not every plant recruits the same organisms. And the outcome depends heavily on soil, moisture, oxygen, pH, management and the organisms actually present.
But the fundamental point remains:
The plant is an active participant in creating its root microbiome.
Water behaves differently beside a living root
This may be particularly important for gardeners as hotter and drier conditions occur.
A root growing through drying soil has a physical problem.
As soil dries, gaps can develop between soil particles and the root surface.
Once contact is lost, movement of water to the root becomes more difficult.
Mucilage changes that interface.
It can absorb and retain water and help maintain contact between roots and surrounding soil.
Rhizosheaths can also reduce air gaps and help maintain a pathway for water movement towards roots.
A 2026 review describes the rhizosheath and its microbiome as a potentially important drought-resilience system. How Earthfood Living Microbes work is in this sphere directly as living functional soil microbes. (not qaterborne).
It is biology operating within physical conditions.
Minerals in the soil are not the same thing as nutrients available to plants.
This is another reason the root interface matters. A soil test can tell us that a mineral exists. That doesn't automatically mean a plant can access it.
Minerals occur in different chemical forms. Some are readily available. Others are bound within minerals, organic matter or chemical complexes.
Biological activity around roots can change that environment.
Microorganisms and roots produce organic acids, enzymes and other compounds capable of altering nutrient chemistry. Mycorrhizal fungi extend into soil beyond roots.
Microbial decomposition releases nutrients from organic matter. Biological transformations continually move nitrogen, phosphorus, sulfur and other elements between different forms.
This is why simply asking:
“How much nutrient is in the soil?” is not enough.
We also need to ask:
“What biological processes are functioning around the roots?”
This is where modern gardening went backwards.
For decades we simplified plant nutrition into numbers on a packet.
N. P. K. Add nutrient. Add more nutrient. Correct the deficiency. Green the plant.
Repeat. There is certainly a place for measuring plant and soil nutrients. Plants require minerals. But reducing soil fertility to nutrient inputs ignores the living system responsible for cycling those nutrients.
A forest does not receive a weekly bottle of soluble fertiliser. Neither did Earth's grasslands evolve with scheduled nutrient applications.
Living systems evolved through relationships between plants, microbes, fungi, animals, organic matter, minerals, water and atmosphere.
The remarkable microscopic world around a root helps explain how.
**Gardeners(and farmers) therefore need to stop asking only, “What should I feed my plant?”
There is another question:
What is happening around its roots?
Does the root zone contain oxygen? Is it waterlogged? Is it repeatedly drying to the point biological activity collapses? Is organic carbon available? Is the soil compacted? Does water infiltrate? Are aggregates forming? Is there living microbial diversity?
Have repeated chemical inputs altered the biological environment? Are roots actually exploring the soil? Do roots have the habitat they need to interact with microorganisms?
Because pouring another product over the surface does not automatically repair the system beneath it.
**And this is the difference between feeding a plant and rebuilding a soil system
Earthfood's interest has always been below the surface. We are interested in the living functional biology of the root zone. Not merely making leaves green for a few weeks.
A functioning biological system should ultimately produce outcomes we can observe or measure by better soil aggregation; water moving through soil rather than running from it; roots exploring a greater soil volume; changes in nutrient cycling and availability; greater biological activity; improved plant performance; and, over time, a soil environment capable of doing more of the work itself.
Introducing microorganisms alone cannot manufacture all of these outcomes regardless of conditions.
Biology must establish. It requires suitable habitat. Water, oxygen, carbon, temperature, soil chemistry, plants and management matters. It all matteres.
That is why Earthfood should never be understood simply as another input replacing one bottle with another.
The objective is a functioning root–soil–microbial system.
Perhaps we have been looking at plants from the wrong end
Gardeners admire the flower. Farmers measure the crop. We diagnose the leaf. We photograph the fruit. But underneath every one of those visible outcomes is another world.
A root pushes through soil. The plant releases carbon compounds. Mucilage forms around the growing root. Microorganisms arrive and colonise. Bacteria produce extracellular polymers. Fungal hyphae explore surrounding soil. Root hairs increase the contact area. Soil particles become attached. Water is retained and redistributed. Minerals move through biological and chemical pathways. The root environment becomes physically and biologically different from the soil only millimetres away.
That microscopic border between plant and Earth may be one of the most important environments in the entire garden.
And most of us were never taught that it existed.
A plant doesn't simply grow roots into soil. It changes the soil around its roots and helps create a living habitat there.
THE FOUR WORDS TO REMEMBER
RHIZOSPHERE: soil influenced by roots.
RHIZOPLANE: the root surface.
BIOFILM: microorganisms living together in a hydrated matrix.
RHIZOSHEATH: soil tightly adhering around roots.
MUCILAGE: the remarkable plant-produced biogel helping connect the root, microbes, water and soil.
Research behind this article
Nazari et al. (2022)
Biogels in Soils: Plant Mucilage as a Biofilm Matrix That Shapes the Rhizosphere Microbial Habitat.
Frontiers in Plant Science.
DOI: 10.3389/fpls.2021.798992
Philippot et al. (2013)
Going back to the roots: the microbial ecology of the rhizosphere.
Nature Reviews Microbiology 11:789–799.
DOI: 10.1038/nrmicro3109
Danhorn & Fuqua (2007)
Biofilm Formation by Plant-Associated Bacteria.
Annual Review of Microbiology 61:401–422.
DOI: 10.1146/annurev.micro.61.080706.093316
Bonfante & Anca (2009)
Plants, Mycorrhizal Fungi, and Bacteria: A Network of Interactions.
Annual Review of Microbiology 63:363–383.
DOI: 10.1146/annurev.micro.091208.073504
Aslam et al. (2022)
Rhizosheath: An adaptive root trait to improve plant tolerance to phosphorus and water deficits?
Plant, Cell & Environment 45:2861–2874.
DOI: 10.1111/pce.14395
Geoderma (2023)
Rhizosheath: Distinct features and environmental functions.
Geoderma 435:116500.
DOI: 10.1016/j.geoderma.2023.116500
Huang et al. (2025)
Trends in rhizosheath research: Formation, functions and methods.
Environmental and Experimental Botany 237:106217.
DOI: 10.1016/j.envexpbot.2025.106217
The Root's Hidden Ally (2026)
Review of the rhizosheath microbiome and drought tolerance.
aBIOTECH 7, 100015.
DOI: 10.1016/j.abiote.2025.100015
Bronwyn Holm, Founder, Earthfood®
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© 2026 Bronwyn Holm. All rights reserved.
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