The ability to predict across environments when a perennial, cool-season, forage grass cultivar will begin inflorescence emergence would allow plant breeders, agronomists and grass-seed marketers to better position that cultivar into a forage production system. Our objective was to determine the affect of longitude, latitude, elevation, cumulative growing degree day (GDD), photoperiod (PP) and cumulative photosynthetic active radiation (PAR) on grass maturation in the spring. Reproductive development was monitored in established cultivars of festulolium (x. Festulolium spp.), orchardgrass (Dactylis glomerata L.), ryegrass (Lolium perenne L. and Lolium multiflorum L.), tall fescue (Festuca arundinacea Schreb.), and timothy (Phleum pratense L.) at eight locations in eastern North America during the spring of 2004 and 2005. For all species, the day of year (DOY) increased and cumulative GDD decreased at 1% inflorescence emergence as latitude increased. Averaged across locations, orchardgrass, festulolium, tall fescue, ryegrass and timothy began inflorescence emergence on 24, 25, 26, 29 May, and 3 June, respectively. Longitude, elevation, and cumulative PAR were poorly related and latitude, cumulative GDD and PP were closely related to the onset of inflorescence emergence. Further study is warranted to elucidate the response of additional species and cultivars to ecogeographic variables and identify additional variables that may affect inflorescence emergence in timothy varieties.