Food Plants - PerennialLandPlant SystemsSoil Erosion & ContaminationSoil RehabilitationTerraces

Vetiver Grass – A Hedge Against Erosion

PIJ #54, March – May 1995

Soil erosion is perhaps the world’s most chronic environmental problem that is literally costing the earth. The soil it carries off now totals 20 billion tons a year and this loss is not only severely degrading the environment, it is eroding the economic viability of countries. Despite enormous effort, standard soil conservation methods have been largely unsuccessful. However, a remarkable tropical grass may hold the key to a cheap, practical solution for controlling soil erosion on a huge scale in tropical and semi-arid regions. It also has many attributes that make it useful to farmers.

Vetiver (Vetiveria zizanoides) is a densely tufted, perennial clump grass with stiff leaf bases which overlap.

It forms narrow, dense hedges when planted along the contours of sloping land, slowing down run-off and helping the water soak into the soil rather than washing off the slope. The stiff foliage also blocks the passage of soil and debris which gradually builds up a soil terrace.

This deeply rooted, persistent grass has restrained erodable soils for decades in India, the Caribbean and in Fiji, where its use was discovered by John Greenfield in the late 1950s.

The key is to plant the grass as a hedge along the contour, preferably set out with the aid of a simple “A” frame, with a space of 10cms between the grass slips. Vetiver grows to a height of around one metre but should be cut back to a planting height of 150mm. The thatch can then be placed behind the newly planted slips to provide an instant filter to control run-off. We did this with amazing results on an urban-fringe forestry programme to control erosion on bare, decomposed granite soil on the hills above Hong Kong. The night after planting saw a very heavy tropical rainstorm. We went next morning and found that two inches of soil had been held back behind the intact grass hedge.

Vetiver is a live system, rather than engineered (bulldozers, graders, bunds, contour drains), which grows with the deposition of sediment. In Fiji, vetiver hedges which have been in position on 20 percent slopes for thirty years have built up terraces two metres high. Experimental plots in Colombia showed significant soil loss reductions using vetiver hedges, where in one year, soil losses were reduced to 1.4 tons per hectare compared to 143 tons per hectare for a bare fallow control.

Best results arise from a two metre vertical interval between hedges, but this depends on the degree of slope and the friability of the soil. On our friable soils in Hong Kong a double staggered row had the best effect. The edges of unsealed roads and drainage ditches can also be protected by vetiver.
Because of their basal density, vetiver hedges are far more effective in controlling erosion than lemongrass or hedges of trees or shrubs such as Leucanea.

Widely adaptable

Vetiver is a native of northern India and southern China, growing where the annual rainfall is more than 300mm, or 600mm where there is a six month dry season. It can also survive more than a month of submergence. Its growth is limited by frost. Vetiver grows in soils from pH 4.5 in Ethiopia and China to pH 10.5 in India and in saline soils up to an electrical conductivity of 4.0.

Minimal Space Requirements

Vetiver has an upright growth habit, although hedges perform best when kept 500mm high and wide. This means that vetiver hedges can be introduced on farms with minimum changes to the existing farm layout. Because vetiver roots grow vertically for at least three metres, not only do they bind the soil, but they do not compete with neighbouring crops for water and nutrients, unlike agroforestry alley cropping systems. Vetiver can be planted along the edge of existing terraces to reinforce the banks against collapse. The oil in vetiver roots also appears to be a deterrent to burrowing rats.

Low Maintenance and Many Uses

An annual trim is all that is needed to keep a vetiver hedge in good shape. It is important to keep the grass from flowering otherwise the stem will die back, which inhibits tillering and slows the growth of the clump (although the clump grows from the plant’s centre so there is no disintegration). The cut material makes excellent thatch or mulch for trees. It may be used as an animal feed supplement and can be fed with a high protein fodder such as Amaranthus, while the Chinese feed it to grass carp. Vetiver also regrows rapidly after fire, although it is very fire-resistant when green and may be used as fire breaks.

Ease of Propagation

Most varieties of vetiver are naturally sterile hybrids and do not set seed, nor does vetiver produce stolons, so there is no danger of the grass spreading from where it is planted. Propagation could not be simpler. Large clumps are split up to give around five to six slips which may be planted bare rooted with a little slow release fertiliser in the same way as forestry seedlings. If a nursery bed is sited on a sandy soil the digging up of the stock plants will be easier. Gaps in an existing hedge may be filled by layering a flowering stem which will root out from the nodes. The grass can also be propagated from nodal cuttings for growing in polythene tubes as is done with forestry seedlings.

Where’s the Catch?

If vetiver is so wonderful, what is the catch? So far there doesn’t seem to be one despite much research.

In parts of India, vetiver hedges have been in place for two hundred years. The grass is non-invasive, does not appear to have any significant pests or diseases and does not harbour vermin. The denseness of the root and basal leaves also forms a barrier to the spread of invasive stoloniferous grasses such as couch and kikuyu and can be used as a border around gardens. We have found that tree planting by itself does not prevent soil erosion for some time, but by planting vetiver grass we are able to have an immediate impact on erosion. The other important function of vetiver is that it forms a windbreak to slow the force of winds sweeping up the bare hillside, so that native grass and herb seeds are not blown away and have a rapid growth of native ground covers that provides the second line of defence against erosion. The trees provide the third line. After about the fifth year, our trees close canopy and the vetiver is affected by shade. However, after thinning the trees or after a fire the vetiver rapidly grows again to keep erosion in check.
There are five other vetiver species which are native to Australia, including Vetivera filipes, usually found in damp areas and on river banks in Queensland and New South Wales. Vetivera nigritana is the main African species and is found from Senegal to Mozambique. It would be interesting for someone to carry out trials of these native types to see if they perform as well as V. Zizanoides in their home areas.

Ideal for Keyline

Vetiver grows with the land, and so appeals to those who actually use the land, the farmers and foresters who are more concerned with increased production from crops and trees than stopping erosion itself. Vetiver is ideal for use in Keyline systems.

Given the vast areas of bare, eroded hillsides in the tropics, or those areas of south east Asia that are covered with unproductive Imperata grass, in which vetiver grows with no problem, I see great potential for its use. I am convinced that the combination of vetiver with Acacia mangium or Peltophorum pterocarpum, which can shade out Imperata, can bring these lands into effective production and put forests back onto the hills.

Extra Design Notes: If there is the possibility of zero annual rainfall, don’t use vetiver alone on contour banks as the roots could die and collapse the soil. Vetiver grows better in semi-arid regions if cut regularly and should be planted in summer, and watered until established, otherwise it will struggle.

 

Tags

38 Comments

  1. refreshing, an article that’s not about politics. Not that i don’t like politics, I just prefer grass. Thanks for the post.

  2. An excellent and accurate article by Richard Webb. I have been using vetiver grass to control soil erosion on various Pacific Islands for almost 20 years and have yet to discover any problem associated with it. The vetiver grass plantings have made very positive impacts on coral reef sedimentation while also allowing the restoration of indigenous forest on the worst types of gully erosion.

    Check out:https://www.vetiver.org/VAN_REEF/VAN-reef2.htm for further details. An email address is included there if further information is needed. I will be happy to forward a higher definition version of that presentation.

  3. Vetiver or khus khus grass does a wonderful job filtering sediment but is not a substitute for swale and berm, which allow actual water storage and infiltration. Note that it is mycorrhizal, so put some old root soil in new planting holes to get the fungi established; don’t buy bare, cleaned roots. Only trained personnel should design plantings on more than a 1:1 (45 degree) slope. In Vietnam, poorly designed plantings have failed (no duh!). Don’t use it as forage if you have heavy metals, it will uptake them. Suitable for planting one plant wide on property borders; forms underground hedgerow against moles, who hate it.

  4. I cannot agree with the comments regarding swale versus vetiver hedge. The sediment trapped by the contour vetiver hedge also contains any light organic matter that is washed downslope – animal dung, leaves etc. Because of this a very high infiltration rate can be maintained above the hedge. In a swale light organic material floats and mainly fine sediment sinks to the bottom creating a silt layer of low permeability.

    A swale has a high risk of overtopping with consequential concentration of water flow and disastrous rill erosion. That cannot happen with a vetiver hedge. They are self leveling as any low spot traps a greater amount of sediment – magic.

    The roots of the vetiver plant facilitate infiltration, possibly by penetrating compacted soil horizons, although other mechanisms may be significant.

    My own work in the Pacific has shown that small catchments that had effectively no water storage developed quite different hydrological characteristics after vetiver hedges had trapped moving sediment and formed just small terraces. The water stored during rain events in those terraces was released over several days, which illustrated just how much water had infiltrated and how it had been retained in the trapped sediment.

    Don’t underestimate the value of the vetiver hedge until you have tried it. I have been using the technique for 20 years now without disappointment.

    Don Miller
    Vanuatu

  5. Ref: vetiver and infiltration. The standard practice in Ethiopia for soil and water conservation has generally been through the use of terraces known as “fanyaju”. This has led to many problems not least the habit that they provide for rodents. Over the past 20 years Ethiopian wetlands have dried up. following the introduction of vetiver hedges there has been significant improvement in wetland restoration dues to vetiver’s capacity to improve rainfall infiltration. These changes are so significant that the Ethiopian Wetland Association is one of the leading promoters of watershed stabilization using vetiver. There is an interesting article at:https://www.vetiver.org/ETH_WORKSHOP_09/ETH_A2a.pdf

    Other evidence from Ehiopia shows the newal of year round potable spring water in areas where vetiver has been used extensively for upland soil and water conservation.

    The issue of mycorrhiza. Containerised vetiver will usually have mycorrhiza when planted out. However it is expensive to propagate in this way. Bare rooted plants normally grow very well and will acquire mycorrhiza in the process. At least 95% of the vetiver planted world wide is bare rooted.

    Heavy metals: research indicates that except for lead most of the heavy metals are retained in the roots of vetiver and that it is safe to use the leaves for forage, mulch etc.

    Slope stabilization: whatever slope it is important apply the technology correctly. Failures reportd in Vietnam were due to (a) some untrained contractors been used for planting and (b) failure due to inherently difficult slopes and soils where the failure surface is lower than the depth of the vetiver roots.

    Dick Grimshaw

  6. As the man that started the modern vetiver revolution way back in fiji in the 1950s, I would appreciate your getting my name right, not as quoted in the above ” This deeply rooted, persistent grass has restrained erodable soils for decades in India, the Caribbean and in Fiji, where its use was discovered by John Greenwood in the late 1950s” GREENWOOD I am not, try John Greenfield!

    1. Hi John, the use of the name Greenfield while being incorrect does describe well the results of your work. Maybe its a sideways compliment. Hope you have a great day. Tim

  7. would vetiver be suitable for areas with regular winter frosts? I can’t seem to find where I could obtain some from, does anyone know of a good supplier in Australia?

  8. Great post. I have used vetiver extensively around my small 1 acre block in an effort to stabilise a gully and also as a chop anc drop plant to assist in weed control.

    Strangely I have found that the plants which I put along my gully have tended to do very well for the first year or two, but then die back. I’ve chopped them back heavilly when this has occurred, but they have either not come back, or come back poorly. In future I will follow the advice above and keep the plants to about 50cm high and also prevent them from seeding – perhaps that will help. Can anybody advise how close to the ground you can cut back without it doing the plant any damage. For these plants which have died back substantially, should I chop them right back to ground level?

  9. Hi Paul. Where are you located? In climate zones marginal to Vetiver growth the shading of the soil by foliage as the plant matures can lead to significant lowering of soil temperature. In Gisborne, NZ, (38 S) my very healthy 2 year old plants had mostly died by year 4.

    I found I needed to mow in early summer down to a height of about 25mm and rake all debris off the soil to allow direct solar radiation onto the soil. On a sunny November day that could lead to an increase in soil temperature of around 5 C at 100mm depth after only 6 to 8 hours. The impact on plant growth was immediate.

    I also had a major problem with cicada nymphs targeting the roots of the Vetiver (around 300 per sq metre) which I put down to inadequate concentrations of the oil in the roots due to the low soil temperatures. Vetiver oil usually has insecticidal properties in tropical zones.

    I would be very interested to hear if you find large numbers of cicada nymphs in your plants – try skimming off the top 20mm of soil and see how many cicada holes you uncover. Mine were centred on the plants like bullet holes around a target.

  10. Don

    I am located in Brisbane. Although it can get quite cold at our place (we get a few frosts most years) I do not think that cold would be the issue. I will take a look for the cicadas.

    I will cut mine right back to the ground as you have. I will do a couple now, but leave the rest until spring to see the different results I get. The problem I have found is that once they die back and are cut back – the remaining dead stalks get in the way of any new growth. Therefore cutting right down – pretty much to ground level, may do the trick in getting a rejuvinated and attractive plant.

  11. We feel this is perfect where we have had major subsidence. It is difficult to find a site to purchase this. Could you please advise of an agency preferbly in southern qld or northern n.s.w.

  12. Try contacting Paul Truong. truong (at) uq.net.au

    Note that he is a very busy man and it could be a while before he has time to respond.

    Cheers
    Don

  13. Hi. does anybody know where I can buy a couple of hundred vetiver slips to trial on my property in NSW Australia?

  14. Hello, could anyone give some clues where to purchase some Vetiver grass, frost seems to be a problem with this species so I would like to trial it in my backyard patch before I purchase a huge quanity for our not so far off degraded property.

  15. what specific mycorrizal species are avsilable in vetiver grass? can i use vetiver grass to in culturing mycorrizae?

  16. Carol,

    The safe, non-invasive, cultivar of Vetiver that is used for erosion control does not have fertile seed. That is its great advantage as it simply cannot become a weed.

    Propagation is done by splitting up a mature plant into small clumps of tillers which are then planted. I believe Duff Swan in Maitland may be able to supply you: https://www.privatelandownernetwork.org/yellowpages/resource.aspx?id=14600

    If not the Vetiver.org website has a link to suppliers: https://www.vetiver.org/TVN_marketplace.htm

    I hope it all goes well. I have been using it in a number of countries since 1990 with good success.

  17. I live in North Texas on very sandy soil where moles are huge problem. Erosion is not such a problem as is lack humate. We run a horse rescue and are trying to improve soil quality. Would vetiver be a good choice though we do get a good number of frost days?

    1. Hi Allen. If the species is still legal in Texas you could try the traditional Burmese technique for controlling moles. They establish Datura plants around fields of root crops and this apparently controls the mole activity. I guess they become disorientated..

      Regarding the lack of humus in your soil, the work of Allan Savory might be of interest to you in that climate. https://www.savoryinstitute.com/about-us/our-team/allan-savory/

  18. I love this article, it is very detailed and accessible, especially the discussion of swales and berms vs vetiver. Why not both? I too am very interested in purchasing organic slips and a non sterile seed variety for essential oil production, as well as erosion control. Do you know of any resources?

  19. Hi Shirley. The non-sterile varieties have two disadvantages. They have not been selected for their oil production (it seems they put energy into seed production instead of root growth) and they have the potential to become an invasive weed. The great advantage of the sterile “Sunshine” cultivar (“Monto” in Australia) is that it cannot be invasive.

  20. i appreciate the efficiency of the grass in controlling soil erosion and helping in soil recovery and reclamation.i will try to find vetiver grass seeds and try soil conservation in the highly degraded usambara mountains,Lushoto.Tanzania

  21. WELL VETIVER IS THE NEW SOLUTION TO HARD ENGINEERING ON SLOPES & EMBANKMENTS. BEEN WORKING ON A PROJECT IN UGANDA AND IT HAS HELP ON BORROW PITS RESTORATIONS AND SLOPE STABILIZATION IN THE RWENZORI REGION, WESTERN UGANDA

    1. Hello Kaaya Ronald,

      I am working on a project near Kasese and am looking for sources of vetiver. Can you tell me where I can find it? Thanks.

  22. Great article Richard. Vetiver truly is one of the worlds most amazing plants. We use it here as a hedge to slow runoff and erosion and aid infiltration. Now that the system is aging and covered in groundcovers it is mainly used instead of a swale to hold water and let it infiltrate. Added benefit that I didn’t think of in the early days is that the roots have actually worked to break up the clay layer that I have in my soil. Awesome :)
    If you want to see how we use it here check out https://pobblebonk.com.au/vetiver/ where I have written about it. Shows how it can be used on the suburban scale.

  23. This verifier sounds great. I am dealing with river bank erosion in Hawaii. The land is about 4 feet above the high water mark of the river. There is about four inches of top soil and then it turns into hardened sand. The erosion happens by the river scouring and undercuting the lower bank and then the top falls in. Would Vetiver roots extend into a hardened sand growing medium, and if so would the roots hold the sand together?

  24. I am considering planting a hedge of vetiver along & behind a residential bulkhead on Lake Conroe, Texas (southeast, one hour north of Houston). It sounds perfect for erosion control & landscaping purposes. Reactions/input/advice from the experts?

Leave a Reply

Your email address will not be published. Required fields are marked *

Related Articles

Back to top button