Evaluating landscape rose performance on reduced irrigation

Water conservation has become a critical issue in urban landscapes in summer-dry climate regions where irrigation must be applied to keep plants healthy. Part of the strategy for reducing landscape water use is incorporating plants with low water needs into the design. To implement this, landscape professionals need information on which available plants can perform acceptably in the landscape on low water, but research-based plant water-use information is often unavailable. Since 2005, University of California researchers have performed trials to evaluate in-ground landscape plant performance on four levels of reduced irrigation, including 10 Rosa hybrida cultivars between 2009 and 2016: ‘Aushouse’, ‘Gruss an Aachen’, ‘KORbin’, ‘KORelamba’, ‘KORfloci01’, ‘KORsixkono’, ‘KORsteimm’, ‘Meidrifora’, ‘Meigalpio’, and ‘Meijocos’. The irrigation treatments were based on levels of reference evapotranspiration (ET(0)) at 20, 40, 60, and 80% of ET(0) in a water budget model using data from a nearby weather station in the California Irrigation Management Information System. After one year of establishment irrigation at 100% of ET(0), irrigation treatments were applied during the second year to six plants of each cultivar on each treatment. Data taken monthly were growth measurements and quality ratings of foliage, flowering, pest tolerance, disease resistance, and overall appearance. Statistical analyses using ANOVA and Tukey’s HSD showed no significant differences in growth between treatments at p≤0.05. For several cultivars, some or all quality parameters were higher on one or more levels of irrigation than others. While some cultivars performed best on the 60% ET(0) treatment, most performed acceptably at 40 and 20% of ET(0) as well. These data have been used to make recommendations for grouping plants by water need in the landscape and in facilitating optimization of landscape water applications