Growing interest in the ecology of cities is providing a unique opportunity for horticultural scientists to study plant processes in an environmental setting that is foreign to most ecologists. Past studies in urban plant ecology have been limited to inventories and distribution of the plants present or have focused on areas of remnant native vegetation and impacts of urbanization on those remnant patches. Classic ecological pedagogy depicts exotic species as invaders, and human manipulations of the geo-surface as disturbance events. The real essence of urban vegetation as a system that has been carefully designed and is intensively managed to serve human interests has been overlooked. While the concepts of human/plant interactions are common and inherent to horticultural research, they may present a difficult obstacle to be overcome for those trained in conventional ecological circles. In conjunction with the Central Arizona Phoenix Long Term Ecological Research initiative, we have approached plant ecological studies in an arid urban system as an interacting triad of plants, people, and the physical environment. People arrange and manage plants in cities for aesthetic as well as practical purposes. Plant viability is predicated on horticultural practices, and the anthropogenic environment in which landscape plants grow can be physiologically stressful. At the same time, the arrangement of plants affects the biophysical environment of the city and the quality of life of the people living there. We propose that a better understanding of urban plant ecology is attained using a landscape horticultural perspective, one that is familiar with the interactions between plants, people, and the physical environment. Understanding the ecology of urban plants might lead to design and management strategies that maximize benefits associated with plants in cities and improve human well being and quality of life.