Vetiver grass in nature

Vetiver grass planted along the road shoulders

       Vetiver grass is a tropical plant which grows naturally. In Thailand, vetiver grass can be found growing in a wide range of area from highlands to lowlands in various soil conditions. The species which is most common in Thailand is referred to in scientific term as Vetiveria zizanioides. This species appears in a dense clump and grows fast through tillering. The clump diameter is about 30 cm. and the height is 50-150 cm. The leaves are erect and rather stiff with 75 cm. of length and 8 mm. of width.
       If planted along contours across the slope, the clump which stands above the ground will produce tillers, forming a green hedge. This thus makes it capable of trapping crop residues and silts which are eroded by runoff and enabling them to naturally form an earth embankment. Since vetiver grass has a deep thick root system which spreads vertically rather than horizontally, it can efficiently endure harsh conditions. The roots densely bind together like an underground curtain or wall enabling it to store water and moisture. However, since the root system expands sideway up to only 50 cm., it imposes no obstacle to the nearby plants and is thus considered an effective measure for soil and water conservation. Vetiver hedgerows maintain soil moisture and soil surface and at the same time, are suitable for cultivating along with economic crops. Growing vetiver grass is simple, applicable and money-saving. The practice can lead to the strengthening and sustainability of the farming system in rainfed areas and can be applied in other areas for preservation and conservation of natural resources such as along the banks of the irrigation canals, reservoirs or ponds along the road shoulders and the approach of a bridge, as well as in forests.

Culm

Vetiver grass is a prolific tiller growing naturally in clumps with thin, long, and erect leaves. The vetiver clumps may grow densely tufted in a big cluster or scattering over the nearby spaces. The base of the clump is dense which makes it obviously distinctive from other types of grass. With the bases of the leaves laying on top of one another, the culm base looks flat. The genuine culm is a tiny shoot hidden in the leaf sheath at the culm base near the soil.
The growth of vetiver is determined by tillering which occurs regularly by producing new shoots on the sides, making the clump bigger and bigger. Normally, vetiver grass has a short culm with unclear joints and pedicels. Aerial branching and culm raising slightly above the ground is not commonly found in fertile conditions, but with vetiver tillers grown in bags, in plots with old tillers or in critical conditions.

Leaf

Vetiver leaves will sprout from the bottom of the clump. Each blade is narrow, long and coarse. The edge of the blade is parallel and the apex is acute. Particularly on old leaves, the edge and midrib are spinulose. Normally, the base and the middle of the blade have few spines whereas the apex has numerous spines. All spines are pointing diagonally towards the apex.
The ligule at the base of the leaf is observable in a shrinkingly bending form with short silky hair which sometimes cannot be noticed.

Roots

Vetiver roots are important and the most useful part. Most grass have fibrous roots which spread out from the underground part of the culm and hold the soil in an horizontal pattern. The roots that penetrate vertically into the soil are not deep. In contrast, the root system of vetiver grass does not expand horizontally but penetrates vertically deep into the soil, whether it be the main roots, secondary roots or fibrous roots.

Inflorescence / Spikelets

Vetiver inflorescence is erect and it appears in the form of a panicle. The panicle and the stalk which is round and long are about 100-150 cm. high above the ground. However, for a mature culm, the stalk can be as high as 200 cm. The inflorescence or the panicle alone is about 20-40 cm. high and can spread out at a maximum width of 10-15 cm. The inflorescence of Vetiveria zizanioides are mostly purple, the colour which is an ordinary attribute of this species.
The spikelet appears in pairs with similar features and size, except for the base of the stalk which has 3 spikelets. Each pair consists of both sessile and pedicelled spikelets. The sessile spikelet is at the middle, whereas, the pedicelled one is at the tip.
Each spikelet is similar in appearance to a spindle. The edge is parallel and oval. The cuneate apex is 1.5-2.5 mm. wide and 2.5-3.5 mm. long. The surface of the back of the spikelet is rough and consists of minute spines, especially at the edge which can be clearly seen. The lower part of the spikelet is smooth.

Seed and Seedling

After breeding, the sessile spikelet which is a hermaphrodite flower produces seeds. Each seed is light brown and in spindle shape. The surface is smooth and the apex and base is round. The inner texture is like sticky flour which turns stiff when exposed to strong wind, concentrated sunlight or other critical climatic conditions. Stiffness disables the seed to enlarge, thus impairing its chance to germinate.
Since the seed can germinate only within a limited period of time and some ecotypes which are imported do not seed at all, the vetiver grass cannot spread like a serious weed.

Culm

Leaf

Root system which is dominated by fibrous roots

Inflorescence

Seedling

Vetiver clump is bushy with the crown part bending down to the ground. The blade of the leaf is grooved at the middle with slim, long tip, and sharp base. At the base, the leaves lay on top of one another and look flat. Vetiver grass propagates by means of tillering like lemongrass. It produces reddish-brown inflorescence with spikelets. After the spikelets fall, new tillers appear at the joints. Tiny vetiver tillers can be eliminated by single ploughing.
Imperata cylindrica Beauv. grows into a continuous pattern of clump because its underground rhizomes hold tightly together. The culm is round and covered with a leaf sheath. The petiole is small and also round. The blade of the leaf is flat. The inflorescence is creamy white and cotton-like which can be easily blown away by the wind. The seed can germinate, thus making the grass become a destructive weed that is difficult to eliminate despite many times of ploughing.

Can Vetiver Grass Become a Serious Weed?

There are voices of concern that vetiver grass may become a serious weed like Imperata cylindrica Beauv. (Laa Laang), Pennisetum polystachyon Schulf. or Mimosa pigra Linn. when introduced into various areas. Generally, vetiver grass propagates by producing new shoots at the joints above soil surface and by branching at the joints below soil surface that have inflorescences. Most spikelets are not subject to fertilization and the seeds which are very thin have a short dormancy period. This thus allows it limited opportunity to germinate and spread like weed. Farmers can control and eliminate vetiver grass easily by digging out the clump or ploughing. It never appears that vetiver grass becomes weed in any areas it has been introduced.

Culm / Leaf

Roots