Growth of vetivergrass for cutslope landscaping: Effects of container size and watering rate

A slope greening technique using vetivergrass has been adopted in Hong Kong on shotcreted surfaces. Vetiveria zizanioides (L.) Nash is the most commonly used species. Soil packed PVC tubes of 250 mm long and 150 mm in diameter are installed on slopes to form planters for vetivergrass growth. However, there is a paucity of information on the optimal tube size for grass growth. Together with soil characteristics, tube size determines water and nutrient availability and the space for growth. This study aimed to assess the suitability of containers of different height and diameter, and the effects of different watering rates on the growth of vetivergrass in a greenhouse experiment. Seven container dimensions and three watering rates were evaluated, and the growth of vetivergrass was measured every three months in terms of aboveground biomass for a year, while underground biomass was determined at the end of the experiment. In general, increasing water supply, diameter and height supported a denser cover of vetivergrass for the purposes of erosion control and decorating hard surface of cutslopes. Vetivergrass grew better when watered at rates equivalent to 1× and 2× the amount of annual precipitation than that at 0.5×, but the effect of watering diminished with decreasing diameter and height. Grass dry matter production increased with the diameter and, to a lesser extent, height of the PVC tubes. If watering is not possible, i.e. under 0.5× or 1× watering rate, a PVC tube with 250 mm height and 150 mm diameter seems to be the most suitable container. On the other hand, if irrigation is feasible, a smaller container can be used without detrimental effect on grass growth.