Vetiver hedges in cooler climates can be challenged by fast growing local species of grass and broad leaved climbers, to the extent that the hedge succumbs to the invading weed’s shade and pressure.  As Vetiver – Chrysopogon spp is sensitive to weedicides especially Glyphosate, getting rid of grass weeds in the hedge, especially Kikuyu grass (Pennisetum clandestinum) can be very labour intensive.  However, if Kikuyu grass is not controlled, it can rapidly smother the vetiver and destroy the hedge. Kikuyu rhizomes don’t invade the root area of vetiver grass, but the their stolons can completely infest a vetiver hedge and ultimately all its aerial parts. Broad leaved weeds in the hedge, can be easily controlled with 2,4-D which vetiver is resistant to.

Fortunately vetiver seems to thrive on being burned and as part of its growth pattern, it has a dense production of trash from the previous year’s dead stems and leaves, This provides a great source of fuel and the build up of trash over the years can also effect the growth of the hedge by shading out young regrowth.
Vetiver’s positive response to being burned makes me wonder that over the centuries of being burned, it is now a ‘fire-climax’ plant.  In the photo left, you can see a vetiver hedge burning in the tropics

The resulting regrowth from that fire shows the young growth either side of the ash-line left from the trash fire that was so densely shading the plants in the hedge.  Obviously Vetiver, being a C4 plant needs as much sunlight as it can get for its regrowth, hence the regrowth on the outside edge of the old hedge.  (right picture)
The picture on the below shows an established vetiver hedge in Ethiopia cut right down to the ground, to supply leaves for many purposes – forage: thatch;  mattress stuffing; mulch; ceremonial purposes etc, but the regrowth from the complete plant base is obvious with no blank central line as with the burned hedge line. Was this ash-line a function of the heat of the fire? However, both the cut line and the burned line regrew within a month as complete hedges.
Burning vetiver hedges as a management tool is to be recommended in areas where you do not want to retain the leaves for any purpose.  Burning gets rid of any unnecessary weed infestation; pests and diseases that may decide to try vetiver as a new host plant, and burning is certainly less labour intensive. There is a point though, you would have to be careful that you controlled the fire, as it is very hot and spreads down the hedge quite rapidly.

John Greenfield  June 1. 2015