Technical Abstract: Orchardgrass(Dactylis glomerata L.) is a highly variable, cool-season forage grass naturalized to nearly every continent. In the semi-arid western U.S., orchardgrass must produce forage under a semi-arid summer season where supplemental irrigation is necessary, survive freezing winter temperatures, and yield when grown with later-maturing legumes. Collection efforts have garnered a diverse array of orchardgrass that includes a number of subspecies, yet none of these have been evaluated for orchardgrass breeding improvement potential in a semi-arid cool-season environment. In this study, orchardgrass subspecies from high elevation origins, Mediterranean origins, and those considered as ancestral to current cultivars were evaluated from dry matter yield, heading date, and plant motality under irrigation and under non-irrigation. These accessions were compared to the cultivars Potomac, Paiute, and Latar. Accessions of high elevation subspecies, and three of four Mediterranean subspecies, showed signiicant plant mortality. The cultivars, ssp. woronowii accessions, and ssp. aschersoniana accessions did not have significant plant mortality. Heading dates varied over 22 days, with cultivars among the earliest heading entries. For dray matter yield (DMY), two accessions of ssp. woronowii showed equal or greater values than the three cultivars. Accessions with improved DMY, and later heading dates, over the cultivars were found, with potential to be used in orchardgrass selection and improvement in semi-arid, cool-season environments.