Dennis retired in July 2017 after 36 years of service with the University.  He was granted emeritus status and continues to write and consult on topics related to urban and environmental horticulture, particularly landscape water management.  During his career, Dennis supported and worked closely with green industry groups, U.C. Cooperative Extension colleagues, and U.C. campus-based faculty to organize educational events for landscape-related professionals, retail nursery professionals, agencies, and the public.  He also conducted field research projects, and prepared educational materials that interpreted research results and science-based information.  His educational and applied research programs centered on helping the landscape industry and associated agencies in Southern California resolve problems in managing and using woody plants in urban areas, particularly in landscape water management.  Tree species selection, culture of landscape palms, and managing tree roots and groundcovers were also issues addressed by his programs. Dennis is the technical editor and a contributing author for two editions of the California Master Gardener Handbook, which is an award-winning, comprehensive reference on basic horticulture from the University of California.