ASHS 2024 Conference

Fifteen taxa of shrubs growing in a field in Tucson, Arizona were irrigated with three levels of irrigation based on local reference evapotranspiration (ETo) to assess growth and plant quality. Plants established during 2021 under 80% of ETo and in 2022 were irrigated at 20%, 50% or 80% of ETo. Irrigation was applied 2, 9, and 15 times between April 1 and October 31, 2022 for the low, medium, and high irrigation, respectively. Best performing plants were Asclepias linaria ‘Monarch Magnet’, Dodonaea viscosa ‘Emerald Ice’, Eremophila glabra ssp. carnosa ‘Winter Blaze’, Ericameria laricifolia ‘Aguirre’, Hamelia patens ‘Sierra Red’, Leucophyllum frutescens ‘San Antonio Rose’, Leucophyllum langmaniae ‘Rio Bravo’, Tecoma ‘Red Hot’ and Rosmarinus officinalis 'Arp'. Irrigation did not affect plant growth of these nine taxa from April to October. Monthly visual quality assessment of some taxa was temporarily affected by irrigation, however, all performed acceptable or better at the low irrigation with the exception of Asclepias linaria ‘Monarch Magnet’ which had less than acceptable ratings in July and August for the low and high irrigation treatments. This taxa also had 62% mortality of plants under the high irrigation treatment between July and October. Hamelia patens ‘Sierra Red’ plants had frozen to the ground in winter 2022 and started to regrow in May. Five of the taxa (Dodonaea viscosa ‘Emerald Ice’, Eremophila glabra ssp. carnosa Winter Blaze, Ericameria laricifolia Aguirre, Hamelia patens Sierra Red, and Leucophyllum frutescens ‘San Antonio Rose’) maintained a high overall rating at the lowest irrigation treatment. Two field days were held in August and October 2022 where participants from the green industry and related sectors were invited to rate overall appearance, flowering and foliage of one representative plant from each taxa and irrigation treatment. Ratings from field day participants were similar to those from researchers during that month. Most participants’ favorite plants included the five taxa with consistently high overall ratings, only Dodonaea ‘Emerald Ice’ was among the top four favorites at both field days. All nine taxa tested are low water use shrubs that can grow in the landscape with 20% of ETo in the low desert in Arizona. However, some may benefit from additional irrigation during the hottest time of the year for optimum performance.