Irrigation effects on growth and visual quality of three ornamental grass species

Abstract

Ornamental grasses have become ubiquitous in the landscape and are popular with consumers and industry professionals because of their favorable low-input cultural characteristics. These characteristics include low water and nutrient requirements, decreased maintenance, fast growth and few disease and insect problems. A study conducted at Colorado State University (Fort Collins, CO) examined the effects of four irrigation levels (0, 25, 50 and 100% of potential evapotranspiration (ET)) on growth and visual quality of three species of ornamental grasses (Panicum virgatum 'Rotstrahlbusch' (Rotstrahlbusch Switchgrass), Schizachyrium scoparium 'Blaze' (Blaze Little Bluestem) and Calamagrostis brachytricha (Korean Feather Reed grass)). Averaged across species, maximum plant height and width was observed at the 25% irrigation level. We found that plant dry weight increased as irrigation level increased from 0 to 50% of ET, but there was a decrease in total plant dry weight at 100% of ET. This indicates that watering these species of ornamental grasses at 100% ET may be detrimental to growth and plant quality. The greatest drought stress, as measured by leaf water potential, was found with the mesic species C. brachytricha. Averaged across species, leaf water potential was most negative (greatest drought stress) at 0% of ET and the least amount of stress was observed at 50 and 100% of ET. At the conclusion of the study, visual ratings of plant form, floral impact and landscape impact were highest at the 25% of ET irrigation level. Our research with these three species in Colorado suggests that irrigation at 25% of ET produces the healthiest plants, with greater height, width, dry weight and visual impact in the landscape. This agrees with anecdotal observations that ornamental grasses will perform better in a landscape with limited irrigation and other inputs.