Festulolium [Festulolium loliaceum (Hudson) P.V. Fournier] is a hybrid between meadow fescue (Festuca pratensis Huds.) and Italian ryegrass (Lolium multiflorum Lam.) or perennial ryegrass (L. perenne L.). The ryegrass parentage gives festulolium cultivars marginal winterhardiness in regions with severely cold winters. The objective of this research was to determine if natural selection for field survival resulted in a genetic improvement in freezing tolerance, forage yield, or persistence in northcentral and northeastern USA environments. The component strains of 'Spring Green' festulolium were compared with their unselected parents in a controlled-environment freezing test. The component strains of Spring Green had 186% greater plant survival and 34% greater tiller survival than their unselected parents. Spring Green was compared with its two commercially available parents in a 13-location field test. Spring Green averaged 5.0% higher in 2-yr forage yield than 'Kemal', but was similar in forage yield to 'Tandem' in a 13-location test ranging from Minnesota to Virginia. Spring Green averaged 30% more ground cover than its unselected parents at the six locations within USDA hardiness zones 2 through 4, but was generally similar to its parents outside of these severe hardiness zones. The increased freezing tolerance of Spring Green, obtained by phenotypic selection for field survival at several locations, appears to have resulted in increased adaptation to northern USA forage production environments.