Urban greening, especially tree planting, is often promoted in climate adaptation plans as a way to reduce urban heat. However, in dry, water-limited regions, the effectiveness and long-term sustainability of these strategies are less certain. This research challenges common assumptions about which types of vegetation are best for cooling and explores how local water availability and climate conditions influence the impacts of greening. We integrate scientific research with the knowledge and priorities of communities and decision-makers by collaborating with water utilities and engaging community organizations and educators. These interactions help shape the questions we ask, the data we collect, and how we interpret the results. Using publicly available data, we examine how vegetation, temperature, and water use interact in Southern California. Our findings suggest that future irrigation needs for urban green spaces may increasingly resemble those of agriculture, raising new questions about the viability of greening in arid regions. Additionally, alternatives to trees, such as grasses and shrubs, may offer meaningful cooling benefits while using less water.