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.

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.

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?

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

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

Check out:http://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.