Deficit irrigation plays a crucial role in water conservation in urban landscapes. Calamagrostis ×acutiflora (feather reed grass) is an ornamental grass known for its neat clumps, golden plumes, and fast growth. It is gaining popularity in urban landscapes across arid and semi-arid regions in the United States. However, little is known about its responses to deficit irrigation. A field study was conducted in 2022 and 2023 at the Utah Agricultural Experiment Station’s Greenville Research Farm in North Logan, UT, to assess the effect of irrigation frequencies on the growth of feather reed grass. Reference evapotranspiration (ETo) data from a weather station in the Utah AgWeather System, Utah Climate Center, Logan, UT, was used to determine the irrigation frequency for each treatment. Four hundred plants were transplanted into the field plot, with twenty plants in each of the twenty 2 by 2-meter plots. Eighty plants within four plots were randomly assigned to one of five irrigation treatments, controlled based on 80%, 60%, 40%, 20%, and 0% ETo. Two harvests were conducted on 30 Sep 2022 and 3 Nov 2023, during which plant height, number of tillers, and biomass were recorded. Plants height, number of tillers, and biomass for both years exhibited a linear and quadratic increase as the irrigation frequencies increased from 0% to 80% ETo. In addition, the linear relationship between irrigation treatments and grass height became less distinct in 2023, although grasses irrigated at 80% ETo were taller compared with those at lower irrigation levels. Based on the results, an irrigation frequency of 40% to 60% ETo is recommended for feather reed grass to maintain optimal growth.
