ASHS 2025 Conference

Due to low annual precipitation and high elevation, many residential areas in the Intermountain West region are classified as high-elevation deserts, necessitating the incorporation of drought-tolerant plants in residential landscapes. However, due to the short growing season and low winter temperatures, many commercial water-wise plants often fail to thrive in this region. Native plants from the Intermountain West could serve as low-water-use landscaping alternatives, but their drought tolerance remains unclear. The objectives of this study were to determine the effects of decreased medium volumetric water contents on the plant growth and physiology of four native ornamental plant species, including Asclepias speciosa (showy milkweed), Hedysarum boreale (Utah sweetvetch), Penstemon eriantherus (fuzzytongue penstemon), and Penstemon grandiflorus (shell-leaf beardtongue), in a greenhouse. Twenty-four plants of each species were randomly assigned to an automated irrigation system, and the substrate volumetric water content was maintained at 0.40 (control) or 0.20 m3⋅m−3 (drought) for 50 days. The decrease in substrate volumetric water content resulted in increased proportion of leaves visibly wilted across the four plant species and also impaired their visual quality. However, H. boreale, P. eriantherus, and P. grandiflorus receiving drought treatment where the substrate volumetric water content was 0.20 m³·m⁻³ still showed acceptable visual quality, while A. speciosa exhibited an unacceptable visual quality. However, the reduction in substrate volumetric water content from 0.40 to 0.20 m³·m⁻³ decreased relative plant growth index of A. speciosa and H. boreale by 19% and 17%, respectively, at the termination of the experiment. In addition, the total leaf area of H. boreale, P. eriantherus, and P. grandiflorus decreased from the control to the drought treatment, while the drought treatments reduced the dry weight of leaves of A. speciosa, H. boreale, and P. grandiflorus. To acclimate to the drought stress, A. speciosa and H. boreale modified their specific leaf area. In addition, H. boreale also increased its root to shoot ratio to adapt to water stress. Drought stress impaired the visual quality and growth of all four high-elevation desert ornamental species in this research. Penstemon eriantherus and P. grandiflorus maintained better visual quality and growth, making them more suitable for low water-use landscaping. Asclepias speciosa showed greater sensitivity to reduced water content despite its morphological adaptations to drought.