Climate Ready Landscape Plants: Aesthetic Qualities and Physiology of Landscape Plants in Response to Deficit Irrigation Across the Western U.S.

Abstract

Climate change is causing more frequent and severe droughts in the Western U.S., while concurrently, about 70% of urban water use is delegated to landscape irrigation. Therefore, water conservation techniques in the horticultural space, such as planting water use efficient landscape plants, will be essential to decrease irrigation consumption. Five different taxa, Hibiscus syriacus ‘Gandini Santiago’ Purple Pillar®, Hibiscus syriacus 'ORSTHIB5x1' PPAF, Rosa ‘Meibenbino’ Petite Knock Out®, Rosa ‘ChewPatout’ Oso Easy® Urban Legend®, and Vitex ‘SMVACBD’ Blue Diddley®, were subjected to one of three water deficit treatments in Arizona, California, Oregon, Utah, and Washington. Plants were rated on foliage quality, flowering, pest tolerance, disease resistance, vigor, and overall appearance. Growth measurements were also taken to calculate a plant growth index and relative plant growth index. Stomatal conductance and the efficiency of Photosystem II (ΦPSII) were measured when the treatments were in full effect and were compared to the aesthetic ratings to get a broad picture of plant health. Overall, at individual institutions treatment did not have a significant effect on aesthetic qualities but did have an effect on growth. However, between institutions aesthetic qualities and growth differed significantly. Stomatal conductance and ΦPSII were not affected by treatment, even when controlling for light level. High stomatal conductance and ΦPSII did not necessarily lead to higher aesthetic scores or greater growth. Given this, the taxa tested performed well aesthetically when watered at a lower frequency even across a large climate gradient. Since the plants were still able to retain their aesthetic value and leaf-level physiological functions when watered less frequently, utilizing the taxa tested can help landscape professionals and consumers reduce their irrigation usage. Aesthetically pleasing plants will always be in demand, therefore assessing water use of common landscape taxa will help to inform growers about plant water need.