Vetiver is already so well known in so many countries that any serious threat from its use for erosion control would by now be obvious and widely reported. However, there are fertile types in India that could become hazardous if they are distributed.
A major reason for confidence in vetiver's safety is that the plant will seldom have to be introduced anywhere. It is already found throughout the tropics and has been there for at least a century. Apparently it has never spread in an uncontrolled manner or become a major nuisance. Possibly, such difficulties may be found as people investigate this plant more thoroughly, but, by and large, vetiver has not become a problem.
It is important, however, that only the right kind of vetiver be used. The types of South Indian origin apparently produce nonviable seeds and must be maintained by vegetative methods. Luckily, this is the fragrant-root type that has been spread throughout the tropics. In areas where it has been planted for decades, or in some cases for more than a century, it has seldom (if ever) spread from seed. In a few areas vetiver is reported as an escape, but even there it neither spreads rapidly nor is considered a nuisance.
On the other hand, types of vetiver grown from seeds introduced from northern India into the United States in 1989 have formed seeds and have germinated in areas adjacent to small plots in Georgia. This fertile type should not be introduced to new areas. It has long been used to protect canal banks in irrigated agriculture in northern India and the neighboring Terai of Nepal without becoming a pest or spreading uncontrollably from seed. Nonetheless, at this time, because of its potential hazard, only vegetative materials should ever be planted. Vetiver must never be propagated from seed.
Yes, although by how much will depend on local conditions and is not now known.
A key claim for the vetiver system is that contour hedges of this grass can slow down and hold back moisture that would otherwise rush off and be lost to the slopes. This claim appears to be valid. For example, in Karnataka, India, farmers who plant vetiver can dig behind their hedges and find moist soil when their neighbor's land is parched. Similar observations have been made elsewhere. In many areas, this ability to hold moisture on the slopes, and thus increase infiltration,