Predicting when a perennial cool-season, forage grass seed-head emergence would allow producers to more efficiently manage their resources. Our objective was to determine the affect of ecogeographic factors on grass maturity in the spring. Varieties of festulolium (x. Festulolium spp.), orchardgrass (Dactylis glomerata L.), perennial ryegrass (Lolium perenne L.), tall fescue (Festuca arundinacea Schreb.), and timothy (Phleum pratense L.) were established in late summer of 2003 at eight locations in eastern North America. Grass maturity and environmental conditions were monitored during initial plant growth in spring of 2004 and 2005. A location x variety interaction associated with both day of year (DOY) and cumulative growing degree days (GDD) at seed head emergence was observed for timothy only at the most southern location. Averaged across locations, orchardgrass, festulolium, tall fescue, perennial ryegrass and timothy began seed-head emergence on 24, 25, 26, 29 May, and 3 June, respectively. Latitude where the varieties were grown accounted for an average of 80% of the differences between varieties in DOY at 1% seed-head emergence.  This relationship was linear and maturation rates were not different between varieties of the same species. Cumulative GDD were not as closely correlated to maturity as DOY.  Days and cumulative GDD between 1 and 50% seed-head emergence were inconsistent within a species and not affected by latitude. Longitude and elevation had no apparent effect on maturity. DOY when a variety begins seed-head emergence at one location can be used to predict when that variety will be at the same maturity at another location if the latitude of both locations is known.