On farm management of Vetiver grass hedgerows

With the increasing potential of multipurpose uses of vetiver grass hedgerow (VGH) by farmers it is important to give some thought as to how the hedges are managed – basically planting design, maintenance and harvesting. The primary purpose of VGH is for soil and water conservation, secondary uses include pest control, forage, thatch, handicrafts, waste water clean up, biomass and more.
The basic (primary) design.  Hedges should be aligned on an “average” contour as shown in this figure.
Planting distance within the line should be 15 cm.  In image below left hand row demonstrates optimum hedge density at two years at 15 cm between plants
The linear distance between VGH will vary with slope, the rule thumb spacing for erosion control is at 2 meter Vertical Interval (VI).  Some examples: 1% slope 104 meters apart; 5% slope 38 meters; 10% 22 meters; 20% 10 meters, 25% 8 meters, and  45% 5 meters.  Often farmers on steeper slopes will start with hedgerows further apart, and then later as experience builds up they add more hedgerows between existing ones if needed. whereas on flatter slopes the farmer may have more hedges than actually needed as when used for marker lines (ridges)
On very small fields/farms/gardens planting a vetiver hedge all around the boundary of the area will provide adequate protection as well as demarcating the field boundary.
VGH management. Hedgerows can grow as high as 2 meters or more, but are often cut for various purposes during the year.  It is recommended that the minimum cutting height is 20 – 30 cm.  A 20 – 30  cm high hedge will be dense, stiff and will withstand rainfall runoff. This image can be considered a “perfect” hedge
When to Cut?
Most farmers cut the hedges to harvest the leaves for various purposes.   Depending on the rate of leaf growth vetiver can be cut and harvested at frequencies of three weeks or more.  If  the leaf is for forage frequent cutting assures optimum leaf nutrient values. For handicrafts mature long green leaf is best.  Mature leaves work well for other uses such as thatch, mulch, and less nutritious forage.  If cutting only once a year it is best to cut just prior to the rainy season.
Managing Hedges for pest control
With the growing awareness of using vetiver as a habitat for beneficial insects and as a “dead end” trap crop to control stem borer in maize, sorghum and rice additional considerations should be taken into account including:
(1) From the time of crop seedling emergence, and then for at least 8 weeks, vetiver should be in good flush – in other words fast and lush leaf growth. This period coincides with the rainy season or in some cases when  crops may be irrigated
(2) The maximum spacing for hedgerows should be 60 meters (coincides with spacing for a 4-5% slope)  because a stem borer moth will fly 30 meters in looking for its preferred vetiver habitat. These 60 meter apart hedgerows (key rows) should not be cut. Hedgerows in between could be managed differently, but if managed in the same way as the key hedgerows will provide improved insect attractant efficiency
(3) In China it has been found that if VGH are not used for soil conservation purposes  a vetiver plant every 5 meters within a line of vetiver is all that is required to attract the stem borer moth, so it would be possible to cut the vetiver within the 60 meter key hedgerows ending up with a hedgerow looking like a castle crenelated battlement! The same would be true for maize and sorghum protection.
(4) There are many other very useful insects residing in the vetiver hedgerows. The vetiver has provides benefits for the beneficial insects in 2 ways: structure (hides there and protected against wind etc.)  and food (leaf exudates and dew condensation early in the morning).  We need these insects during the crop season, and out of season, cutting no lower than 30 cm should still provide the necessary habitat for insects. Since generally farmers do not cut all their hedgerows at one time, insects can move from cut to uncut hedges for habitat.

(5) Micro-scale permaculture based operations plant vetiver in many different ways including border edges, interspersing within crops (as single clumps). Such planting patterns provide habitat for pests, mulch, and other benefits, some of which we may not be fully aware of (control of fungi on root crops and vegetables, soil eelworm reductions associated with crops such as chillies, and termite control.)