We don't grow olive trees, we grow soil: how the root microbiome makes polyphenols

By Nicolas Netien, Chief Scientific Officer of Oleaphen

The buffer zone

In 2013 I was asked to design an olive grove in the buffer zone, on dry ground with very limited access to water.

Olives are the right tree for that land and have been for three thousand years. The difficulty is that modern olive growing has largely forgotten how to do it without help. Most of the expansion of the last two decades has been irrigated and fertilised, and the knowledge of how to establish a grove that lives on close to what falls on it thinned out along with the groves that used to prove it.

So the design started with water. We shaped the ground to hold runoff on the contour and put rainwater harvesting above it. Underneath both sat the part that mattered most, which was the soil. Bare mineral soil there sits under one percent organic matter. Rain arrives, some runs off, the rest drains past the root zone within days, and the tree spends August on what is left.

None of that was a guess. Soil biology is what I was trained in and what I had spent close to twenty years applying to crops in dry country. The principle was not in question. What I did not know was which specific approach would perform best on that particular ground, so rather than commit eight thousand trees to one method I split the planting into blocks of one hundred, each with a different soil treatment. Composts of varying origin and maturity. Different microbial inocula. Mulching regimes, cover crop mixes, companion planting with trees and with aromatics. Forty treatments, each replicated across Kalamon and Koroneiki, so any difference could not be attributed to genetics.

I was measuring survival, then vigour, then whether the trees could carry fruit through a Cypriot summer on almost nothing. Polyphenols were not in the brief and I was not thinking about them.

We milled the first oil in 2015, block by block. Most of it was unremarkable. A handful of blocks came back with phenolic levels I had never seen before, high enough to assume laboratory error. We ran them again and they held. Certain soil treatments, repeatedly, across both cultivars, produced oil several times higher in phenolics than trees a hundred metres away on the same slope, picked the same week, pressed through the same mill.

That grove was a commission and it ended, and none of our oil comes from there. What I took away was forty treatments worth of evidence and a decade of work refining what it showed.

The trade going on under your feet

The mechanism is simpler than most of what gets written about farming.

A tree pulls carbon dioxide out of the air and turns it into sugar. Everyone learns that part at school. What gets left out is what happens next. The tree does not keep all that sugar. It sends a large share of it down through the roots and pushes it out into the soil, deliberately, as food.

Estimates vary by species and conditions, but plants generally give away somewhere between 5 and 30 percent of everything they fix to the ground around their roots.

They are paying for something. The sugar feeds bacteria, fungi, and the organisms that eat them, and those organisms unlock nutrients and water the tree cannot reach on its own and deliver them back. Phosphorus, nitrogen, trace minerals, water from pores far outside the root zone. It is a trade, running continuously, in both directions.

That community is the root microbiome, and it works on the same logic as the one in your gut. You do not digest your food alone. Neither does a tree.

Which is why we say we grow soil rather than trees. The tree is not the thing being managed. The tree is what shows up when the trade is working. Get the soil right and it feeds itself, waters itself further into a drought than it should be able to, and defends itself. Get the soil wrong and nothing you do above ground fixes it. You end up spraying and feeding a tree that has no partners left.

The laboratory detail here is genuinely early. Root microbiome research sits roughly where gut microbiome research sat twenty years ago, and there is a lot we cannot yet explain at the level of individual organisms and pathways.

The system-level result is not in doubt, and that is a different question. More organisms and more kinds of organisms produce more stability, in soil as in any other ecosystem. When I started applying this, it was fringe work, and it was treated as such. There are now thousands of farms across every continent running on these principles and demonstrating the outcome daily. The science is catching up to the practice, which is the usual order of things in agriculture.

What fertiliser does to the trade

We do not use chemical fertiliser, and the reason is that it dismantles what I have just described.

Take it from the tree's side. It gives away sugar because that is the price of nutrients it cannot otherwise obtain. Deliver those nutrients directly, in soluble form, and the tree stops paying. There is no reason to fund an expensive partnership when the goods arrive free.

So the carbon flow downward drops. The organisms living on it thin out. This is measurable: inorganic fertilisation suppressed microbial respiration in the rhizosphere of hardwood trees by 36 to 46 percent in one study, and long-term fertilisation trials show reduced diversity in the root-feeding microbiome and a simpler, poorer plant-microbe association overall. A review of plant and rhizosphere chemistry states plainly that modern high-input agriculture has diminished this interaction through synthetic nutrients and pesticides.

You end up with a tree on a drip. Fed, technically. Dependent, completely. And a soil that has lost the biology that used to hold water, cycle nutrients and buffer stress.

That is the reason we do not use it. Not carbon accounting, not marketing. Chemical fertiliser breaks the soil food web, and the soil food web is the production system.

What we use instead is compost, animals moved through the groves, and nitrogen-fixing ground cover. Mostly Medicago, including cultivated alfalfa and vetch alongside wild Medicago ecotypes given to me by the Cypriot seed bank, plus whatever self-seeds and stays. Locally adapted material rather than a bought mix. None of it feeds the tree directly. All of it feeds the soil, and the soil feeds the tree.

Why this shows up in the oil

Polyphenols are not a nutritional bonus the tree produces for our benefit. They are defence compounds. The tree builds them to handle pathogens, insects, UV, heat and drought. The closest everyday comparison, imperfect but useful, is an immune system.

Defence is expensive. A plant invests in it once its basic needs are covered and when it has resources to spare. A tree struggling for nutrients and water puts everything into staying alive. A well-supplied tree with a functioning microbiome can afford to build chemistry.

So the chain runs: living soil, working trade, well-fed tree, strong defence, more polyphenols in the fruit. Every link in it is about the soil.

The laboratory work supports this from several directions. Mycorrhizal fungi, which extend a tree's effective root system by an order of magnitude, are among the most important partners in the trade. Mechri and colleagues found in 2015 that olive roots colonised by these fungi accumulated significantly more phenolic compounds than uncolonised controls. In 2020 the same group added drought to the experiment and found that colonised plants under water stress produced more oleuropein than either stressed plants without the fungi or well-watered plants with them. The partnership and the stress together did something neither did alone.

Those studies measured root tissue rather than oil, and the full chain from inoculation to bottle has not been published as a single piece of work. It rarely is, in agriculture. The evidence that matters here is the kind that accumulates in fields: forty treatments in the buffer zone pointing one direction, a decade of harvests since, and the wider body of practitioner results from regenerative farms worldwide showing the same relationship between soil biology and plant health. Laboratories are confirming a mechanism that farms established first.

There is one more piece, which is water. Mild water stress raises polyphenols. Real drought does the opposite, because a tree that has shut down is not building anything. Organic matter and biology hold water in the profile, which keeps a tree working through the dry months instead of collapsing in August. It stays in the productive range for longer. Again, soil.

Nothing that kills

We apply no insecticides, no fungicides and no herbicides, conventional or organic-approved. The reasoning follows directly from everything above. You cannot spend a decade building a microbial community and then apply broad-spectrum products that kill parts of it.

Our only foliar application is a zeolite particle film, a physical barrier rather than a toxicant. It coats the fruit surface and deters the olive fly from laying, and in field testing its residual deterrent effect has been comparable to a pyrethroid. Codex Alimentarius lists zeolites among substances approved in organic production and plant protection.

We use zeolite rather than kaolin for a specific reason. In comparative trials, kaolin-treated olive trees showed significantly lower photosynthesis and water use efficiency than untreated controls, while zeolitite-treated trees behaved like untreated plants. On a rainfed grove, and given that photosynthesis is what funds the entire underground trade, that difference is not a detail.

What follows from not killing anything is harder to quantify, and I will describe it as what I see rather than as a measured result. Ground cover stays. Predators establish. Pest pressure becomes something that fluctuates rather than something suppressed on a calendar. Over several seasons the thing being managed stops being a crop and becomes an ecosystem with a crop in it, and it asks less of you, not more.

The same carbon, counted

This is where the climate part stops being a separate subject.

The sugar a tree sends into the soil to pay its microbes is carbon it took out of the atmosphere. Some is respired straight back. A significant share ends up locked into microbial bodies, fungal networks and soil aggregates, which is how carbon enters soil and stays there. The transaction that produces the polyphenols is the transaction that builds soil organic carbon. They are not two achievements. They are one process described from two ends.

We did not add a carbon programme to an olive farm. Nothing in this system exists for the carbon.

Using the International Olive Council's carbon balance methodology, our production comes out at a net removal of 16 kg CO2e per litre. For context, the IOC's own reference position is that producing a litre of olive oil emits around 1.5 kg CO2e on average, while a mature semi-intensive orchard has the potential to fix in the region of 10 kg of CO2 per litre. Their calculation tool is still in a pilot phase and the methodology is being refined as growers use it, which I would rather state plainly than present the figure as more settled than it is.

Sovereignty

In February the Strait of Hormuz closed. Within weeks, Middle East granular urea went from roughly 450 dollars a tonne to over 700. Gulf countries supply close to half of global urea exports, and natural gas makes up most of the cost of manufacturing nitrogen fertiliser, so European gas prices and fertiliser prices moved together. I wrote about the consequences for the wider food system in the Cyprus Mail.

Our input cost did not move, because we do not buy nitrogen.

I do not offer that as foresight. It was a decision made about soil biology that turned out to have a second use. But it is worth stating clearly, because it points at something larger than one price shock.

A farm that buys its fertility has handed control of its viability to gas markets and shipping lanes it cannot influence. That is true of most of European agriculture. When the inputs are cheap, the arrangement is invisible. When they are not, an entire sector discovers at once that its costs are set several thousand kilometres away by people who are not thinking about farms.

The same logic applies to water, which for Cyprus is the harder problem. This island has the highest water exploitation index in the European Union. Temperatures are climbing faster than the global average and rainfall has been falling for a century. One wet winter does not change that.

Every percentage point of organic matter built into a soil holds tens of thousands of additional litres per hectare, and that stored water is the difference between a grove that carries fruit through August and one that drops it. Soil is the cheapest and most durable drought infrastructure available, and unlike a dam it improves each year rather than silting up.

So regenerative agriculture does two jobs at once here. It removes carbon, which is mitigation. And it makes a farm able to withstand the conditions that are arriving regardless, which is adaptation. Most climate interventions do one or the other.

What it adds up to is sovereignty. A grove that makes its own nitrogen and holds its own water is not at anyone's mercy. That is not an ideological position. It is a count of how many things can be done to you from outside, and the count is lower.

Five families

Traditional olive groves across the Mediterranean are being abandoned, and the reason is arithmetic. The literature describes them as unprofitable under most production and price conditions even after subsidies, because yields are low and the fruit sells into a commodity market where large buyers set the price. What follows abandonment is erosion, fire risk and the loss of the flora those groves were sheltering.

High phenolic oil changes that arithmetic. It does not sell as a commodity, and it pays enough that a family with a traditional grove has a reason to keep farming it.

Five family farms grow for Oleaphen, trained in these methods. Most are certified organic and the rest are working through the three-year conversion. We are training new families now, because demand is ahead of what we can supply, and this is the part people find hardest to hear: it cannot be solved with money. Soil biology takes the time it takes. A grove in conversion takes three years because it takes three years.

Olive trees set the pace, not venture capital.

Five millilitres

Our 2025/2026 harvest measures 2,236 mg/kg total polyphenols, of which 1,248 mg/kg is oleocanthal, verified by LC-MS/MS at the IOC-accredited laboratory of the Universidad de Cordoba. The certificate of analysis is published in full.

Under EU Regulation 432/2012, an oil qualifies for the authorised claim that olive oil polyphenols contribute to the protection of blood lipids from oxidative stress when it delivers at least 5 mg of hydroxytyrosol and its derivatives per 20 g of oil. From a typical supermarket extra virgin, reaching that means 50 to 100 ml a day. From ours it takes under 5 ml.

That ratio is usually presented as a nutritional argument. It is also an environmental one. Measured per litre, every olive oil looks broadly similar. Measured per unit of the compound you are actually buying it for, the numbers separate by an order of magnitude, and so does the land, water and soil behind each dose.

If you want to see what separates one oil from another at the level of a lab report, or how those oils compare on price and concentration, both are worth reading before you buy anything from anyone.

The September harvest is allocated by registration date. You can join the waitlist, or read more about how we work.

Thank you for reading, and for your patience while the trees do their work. Nature sets the pace here, and we are content to follow it.

---

About the author

Nicolas Netien is Co-founder and Chief Scientific Officer of Oleaphen. He is an environmental engineer specialising in soil biology, regenerative agriculture and Mediterranean agro-ecosystems, a Knight of the Order of Agricultural Merit of the French Republic, and holder of the world record for the highest polyphenol concentration ever measured in olive oil, set with the 2018 harvest.