Water-efficient landscaping can reduce water consumption without compromising the aesthetical appearance of urban landscapes. Penstemon, with more than 250 species available in a spectrum of colors, is a popular choice in xeriscape designs and water-wise gardening due to its ability to thrive in dry conditions while providing attractive visual appeal. However, limited field trials have explored the responses of penstemon under deficit irrigation. This study, conducted at the Utah Agricultural Experiment Station’s Greenville Research Farm, North Logan, UT, USA, from 30 Jun to 31 Oct 2023, was to investigate the overall appearance and canopy temperature responses of three penstemon species: Penstemon barbatus (Cav.) Roth ‘Novapenblu’ (Rock CandyTM blue penstemon), Penstemon pinifolius (pineleaf beardtongue), and Penstemon strictus (rocky mountain beardtongue), under three irrigation frequencies. Reference evapotranspiration (ETo) was utilized to control irrigation frequencies. Eight plants of each penstemon species were randomly assigned to one of three deficit irrigation treatments, calculated based on 80% ETo (high), 50% ETo (moderate), and 20% ETo (low). A monthly evaluation of overall appearance was conducted. Top-view infrared images of plant canopies, from which canopy temperature can be calculated, were captured using a thermal camera. Results revealed that higher irrigation frequency led to better overall appearance, with some variability observed among species and months. Moreover, increased irrigation frequency correlated with lower canopy temperatures, displaying species-specific responses. Further observation is needed to compare the responses of P. strictus, P. pinifolius, and P. barbatus under field conditions.
