The following standards and guides have been corrected and updated:
D4 – VGT – Microbial Root Dips for Vetiver Establishment v3
D5 – VGT – Vetiver and Arbuscular Mycorrhizal Fungi (AMF): Soil Health, Water, and Nutrient Transfer v3
D6- VGT – Vetiver Grass Technology (VGT) for Nematode Suppression and Soil Biological Recovery in Open Fields and Agroforestry Systems v3
D7- VGT – Vetiver as a Dead-End Trap Plant for Cereal Stem Borers v3
D8- VGT – Forage Management of Vetiver Grass v2 (new v2)
D10a- VGT –Three Perennial Grasses Compared–Chrysopogon nigritanus and Chrysopogon zizanioides, and Napier – Pennisetum purpureum v2
D14- VGT – Vetiver and Soil Carbon v2
GVF – Level 1 Observation (tally) Sheet v2
Six months of standards, and what prompted them
Over the past six months TVNI has been building something it did not previously have: a set of design standards and structured guides covering vetiver applications, with the underlying data referenced and, wherever possible, checked. Before that, the technical basis of vetiver work sat scattered across three decades of conference proceedings, newsletters and field experience — much of it sound, little of it in a form a ministry, an engineer or a donor could pick up and use.
Eight of those documents, covering the agricultural applications, have now been through a second pass and been revised as a set. This is part one of the review; the engineering and infrastructure standards follow. The reason for the effort was not tidiness. Something in the field evidence had begun pointing in a direction the standards did not yet cover. Details of the updates are summarized in: Technical update (July 2026)
What farmers kept reporting
For years, and with increasing frequency recently, farmers and field users in unconnected places have reported the same thing: crops growing in close association with vetiver do better than the same crop further out. Not merely better protected from erosion — healthier, more vigorous, less troubled by pests.
Re-reading a 1992 CIAT report from Colombia this year, and writing the discussion paper “The Hidden Benefits of Vetiver” that followed it, suggested why. That report contains a row-by-row cassava yield record between grass, and it points toward a biological explanation rather than a purely physical one. Five mechanisms (and may be more) are candidates, and each is documented at least in part:
Mycorrhizal fungi. Vetiver is an exceptional host, and these fungi extend a plant’s effective reach for phosphorus — which matters most on exactly the poor acid soils where vetiver is usually planted.
• Nematode suppression. Vetiver is a poor host to root-knot nematodes, and its root chemistry is toxic and repellent to them.
• Stem borers, by two separate routes. Moths lay their eggs on vetiver in preference to the crop and the larvae then die on it; and separately, a permanent hedge raises the standing population of the parasitic wasps that attack borers out in the crop.
• Coffee berry borer, through that same parasitoid route.
• Striga. Mycorrhizal fungi suppress this parasitic weed through improved phosphorus nutrition of the host cereal.
What these have in common is the thing that makes them difficult: every one is an effect on the plant growing next to the vetiver, not on the vetiver itself.
From observation to Farm Models to a trial program
Two things followed. TVNI assembled a series of Farm Models describing how vetiver is actually or potentially integrated into working farms — the standard contour hedgerow, the enhanced version with plants set in the middle of the field, the forage bank, the plantation grid for coffee and tea estates, the kitchen garden, the food forest and others. These are not layouts invented for the purpose. They are configurations farmers/gardeners are already or partially running with modification, written down so they can be compared and so the biology can be tested against them.
And the Global Vetiver Farmer Demonstration-Trial Program was developed to find out whether these benefits are real, how large, and how far from the hedge they reach. It is now in its initial start-up phase, with recording instruments in beta and first field testing under way in Ethiopia.
The revised standards and the trial program are two halves of one thing. The standards set out what is known and, more usefully, exactly what is not. The program is built to measure the difference.
Corrections along the way
Nine published figures moved during the six months of work. All of them moved in the same direction — downward, or from a stated fact to an open question.
Our estimate (always difficult) of the soil carbon a vetiver hedgerow builds fell by roughly two thirds. The figure had never been divided by the number of plants in a hectare; when it was, it required each plant to lock more carbon into the soil in a year than a plant of that size grows in total. A statement that vetiver puts 60 to 70 percent of its growth below ground had the ratio upside down — the measured figure is 40 to 45 percent, still two to three times what most grasses manage. And the most attractive idea in the whole vetiver story — that a fungal network extending from vetiver roots pipes phosphorus and water to crops several meters away — has been downgraded from a claim to a research question, because the ecological literature no longer supports stating it as fact.
Corrections are what a wide-ranging program produces, and they should be expected.
TVNI has been active in more than a hundred countries for four decades, across erosion control, slope engineering, water treatment, forage, carbon accounting and pest management. Guidance of that reach accumulates figures faster than anyone can verify them, and the need for correction will not end with this review. What matters is that the process exists, is applied to the flattering numbers as well as the awkward ones, and that the results are published rather than quietly dropped.
What we still do not know
The more useful outcome was not the corrections but the shape of what was left over. Once every document had been marked up to separate what is demonstrated from what is inferred, a pattern appeared that none of us had seen while working on them separately. What vetiver does on its own ground is well established. It stabilizes slopes, it improves rainwater infiltration, it survives drought, it hosts mycorrhizal fungi at exceptional levels, it does not host root-knot nematodes, it takes up heavy metals, it builds soil structure, and it puts carbon into the subsoil. All of that rests on measurements.
Almost everything we do not know concerns what vetiver does for the crop growing next to it. Does a living hedge lower nematode pressure in the adjacent field, and how far out? Does its fungal network deliver anything useful to a neighboring crop, or does the benefit stop at the hedge? Do the parasitic wasps sheltering in a hedge actually reduce damage in the maize, or do we merely have more wasps?
These are the questions farmers care about, because they are the questions that decide whether a hedge is worth the land it occupies. They are also, without exception, questions about distance — about what happens as you walk away from the hedge into the field.
Why a farmer network can settle it
That is a fortunate coincidence, because a gradient is the one thing a farmer can measure well and a research station usually cannot.
The reason is worth explaining, because it is the whole justification for the demonstration program. Most on-farm data is weak because it compares one farm with another, and farms differ in soil, slope, rainfall, management and skill. Any difference you find could be caused by any of those things. A gradient avoids the problem entirely. When you measure yield at the hedge, at five meters and at the midpoint of the field, everything except distance is held constant — same soil, same season, same farmer, same crop, same seed, same weather. The far point is the control, and it sits in the same field.
Why the shape matters more than the numbers
A farmer does not need to weigh a harvest accurately for this to work. Any consistent error in the measuring — a cup that is slightly small, a habit of rounding down — applies equally at every distance and cancels along the transect. What survives is the shape of the curve, and the shape is the finding.
The second reason a farmer network can settle these questions is hedge age. Vetiver hedges get better with time — the root system deepens, the fungal community builds, sediment accumulates. If the biological effect is real, a one-year-old hedge should show almost no gradient and a twenty-year-old hedge should show a strong one. We have said in advance what the pattern should look like, and the network contains hedges of every age. That is a genuine test, and no single research station could assemble it, because nobody funds a trial that has to run for twenty years before it reports.
Third, variety works in our favor. If the same gradient appears in Kenya, Ethiopia and India, across cassava, maize and coffee, with the same dependence on hedge age everywhere, no alternative explanation plausibly survives. Two hundred ordinary fields, each containing its own control, are worth more than one immaculate experiment.
What better data would let us design
This is not measurement for its own sake. Each of these questions currently forces a design decision to be made on judgment that could be made on evidence instead. Five examples.
How far apart should hedges be?
At present we space hedges by erosion control alone — by slope and vertical interval, as soil conservation engineers have always done. That is the right basis when erosion is the objective. But if the biological benefit reaches only five meters, then on a field with hedges twenty meters apart most of the crop is growing outside it, and a farmer whose main problem is nematodes in ginger is getting very little of what vetiver could offer. If it reaches fifteen meters, current spacing is close to right.
Nobody knows which, and the two answers imply completely different recommendations. They may also differ by crop: ginger, tomato or banana could justify hedges at half the spacing a maize field needs.
Does the midfield plant earn its keep?
One of our farm models, V101-E, places individual vetiver plants in the middle of the field between contour hedges — on the theory that the midpoint is where biological influence from both hedges is weakest, and a plant there fills the gap. It is a reasonable theory. It also costs a farmer labor and a little land.
The only way to find out is to measure at the midpoint on farms that have grid plants and farms that do not, and see whether the dip in the middle is shallower on the first group. That comparison already exists inside the network. It needs no new trial, only the midpoint measurement.
Should the hedge be cut, and how short?
Our own guides currently give four different answers, because they were written for four different purposes. Do not cut at all in season, says the stem borer guide, because a tall hedge is what the moth finds. Never below about fifty centimeters, says the nematode guide, to keep the roots working. Cut in thirds, says the mycorrhizal guide, to keep feeding the fungi. Cut to twenty or thirty centimeters, says the forage guide, because that is what a farmer harvesting fodder actually does.
All four are defensible in isolation, and a farmer with one hedge needs one answer. Comparing cut and uncut sections of the same hedge on one farm — borer damage, root galls, yield either side — would give it. This is now being recorded in Ethiopia.
Which side of the hedge, and is the benefit even biological?
There is an honest objection to everything above. A hedge traps soil and holds water, so the ground immediately above it is deeper and moister than the ground in the middle of the field. That alone would produce a yield gradient with no biology involved.
Telling the two apart costs nothing. Sediment collects on the upslope side of a contour hedge; fungal networks spread both ways more or less equally. So an effect strong above the hedge and weak below it is soil, and an effect appearing on both sides at similar strength is biology. Our revised field forms will, following ongoing Ethiopian testing outcome, record above and below separately at every distance, and measure how much soil has actually built up against the hedge, so the two explanations can be separated rather than argued about.
Root gall counts settle it from the other direction. Accumulated sediment does not suppress nematodes. If galls fall as you approach the hedge in the same field where yield rises, the mechanism is biological and the argument is over. That measurement needs no laboratory and no equipment beyond a fork, and it is the most valuable thing in the program.
When should a farmer expect to see anything?
This may be the most practically important of all, and at present we cannot answer it honestly.
The 1992 CIAT trial offers a clue. A first-year vetiver seedling planted the same day as the cassava gave yields indistinguishable from a field with no hedge at all — in its first season it did nothing, good or bad. It stayed out of the way. A mature elephant grass hedge in the same trial cut yields by nearly a third. Whatever benefit vetiver offers had not arrived in year one.
If gradient strength does scale with hedge age across hundreds of farms, we will be able to tell farmers and funders something we currently cannot: neutral in the first year, measurable by the third, strong by the tenth. That changes how programs are financed, how expectations are set, and — importantly — it protects the technology from being written off after a single disappointing season by someone who expected results too early.
Where we are now
Three recording instruments are in beta. A citizen-science form for anyone with a single vetiver hedge or even one clump, which asks for very little and accepts whatever a person can see. A fuller Level 1 form for registered farms running one of the seven GVF farm models. And a field tally sheet designed for a single recording pass, currently being tested in Ethiopia.
All three record the same core — hedge age, distance from the hedge, crop yield, root galls, and where relevant Striga counts, borer damage and days to wilting. All three will be revised after the first season, which is the point of testing them.
None of them use control plots, and that is deliberate. The gradient already contains its control. Asking a smallholder to set land aside would cost participation and add nothing the far end of the same field does not already provide. Control plots belong at Level 2, where the question shifts from whether an effect exists to what is causing it.
The Ethiopian tally sheet has gone further than we asked. It records soil accumulated against the hedge divided by years since planting, which quantifies the sediment explanation directly, and plow pan depth, which tests whether the fungal reserve really sits below cultivation depth. It also records failures — breached bunds, abandoned maintenance, and why repairs stopped. Programs in this field rarely collect their failures, and those records will be worth more under external review than another success story.
The point of all this
Vetiver has been promoted for forty years on the strength of what it does to soil and water, and that case has never been in doubt. What has always been claimed alongside it — that a hedge makes the crop beside it healthier and less troubled by pests — rested on farmer observation and reasonable inference. Farmers believed it, and were generally right to. But we could not prove it, nor say how far the effect reaches, how long it takes to arrive, or how to design a field to get more of it.
That is now a solvable problem, and solvable by farmers rather than institutions. The revised guides say precisely what is unknown and what measurement would resolve it. The forms collect it. The network supplies the range of soils, crops, climates and hedge ages that makes the result convincing.
The evidence has been sitting in plain sight for thirty years — in a 1992 paper on our own website, and in the fields of farmers who kept planting vetiver because they could see it working. What the past six months have done is set the standards down in structured form, clear away the numbers that would not stand up, and state exactly what we still need to know. The next part is measurement.
If you have a vetiver hedge
You can contribute. The most useful record is a simple one: how old the hedge is, what crop grows beside it, and how that crop compares close to the hedge against the middle of the field. A gall score and one photograph is already a contribution — and an old hedge showing a strong gradient is the most scientifically valuable observation anyone can send us.
Forms and guidance: vetiver.org · [email protected] · WhatsApp #GVF