University of Washington, Seattle
OP-T2-47: Xeriscaping

Xeriscaping is the significant reduction or elimination of supplemental irrigation through plant selection and horticultural practices. To this, the UW encourages native, drought tolerant, and naturalized plantings. However, even with such plant selection, the local Mediterranean climate typically requires some supplemental irrigation in the summer months and the UW has found this is most efficiently provided via networked, underground, high efficiency, weather informed, automatic irrigation and well trained staff. Furthermore, UW also encourages other cultural practices to minimize supplemental irrigation such as aeration, soil protection during construction, proper soils, soil amendments and soil preparation, mulching, hydrozoning plants with similar water requirements, matching plants with compatible microclimates, annual commissioning and continuous maintenance of irrigation systems for proper function and efficiency, and ongoing upgrades to improve existing irrigation systems and provide new irrigation systems to replace obsolete systems or for areas that were previously manually irrigated. Next, xeriscaping is often characterized by relatively wide and limited plant spacing, bare gravel and soil buffers in between plants, and point source plant-specific irrigation, often typical in more arid climates. However, in the northwest, design practices include plant spacing at maturity to cover fertile soils to minimize weeds, and accordingly, full irrigation coverage via sprinklers with head-to-head spacing or gridded subsurface drip irrigation is needed to provide efficient irrigation for such mass planting root zones. Nevertheless, the UW champions a local variation of xeriscaping to start new trees. To improve survival and the healthy establishment of new trees, the UW encourages the installation of dedicated point source, tree specific irrigation zones which are operated for two to three years then retired from service. Similarly, as an alternative to plumbed irrigation, short term tree specific irrigation is provided via installing incrementally spaced tubes around new tree root balls and filling them with time release water suspended in a microbe activated cellulose gel. Last, the UW has the added challenge of managing some non-native or non-drought tolerant plant and tree specimens to provide a diverse collection in support of several academic and research programs as well as a public tree tour.