Winter hardiness in barley (Hordeum vulgare) is a trait targeted by breeding programs in order to expand the potential area of adaptation of fall-sown cereals. Vernalization requirement is an important factor in winter hardiness. A vernalization requirement is an extended period of low temperature required for transition from the vegetative to reproductive states. A model involving two vernalization genes that interact in an epistatic fashion to determine the vernalization phenotype has been proposed. To test this model, the vernalization phenotype was compared to the vernalization allele genotype for each entry in a breeding program nursery grown under fall- and spring-sown conditions. The number of growing degree days (GDD) from planting to Feekes growth stage 10.5 was recorded for each line in both experiments. Lines that did not reach Feekes 10.5 when spring-sown were assigned values of 1000 GDD. To calculate the growing degree day vernalization coefficient (GDD-VC), the fall sown GDD value was subtracted from the spring sown value for each line. The GDD-VC values ranged from 139 to 812. Facultative phenotypes were classified as <309 GDD-VC or less and winter phenotypes >409 and above. Genotypes were then assessed according to their vernalization allele configuration at the VRN-H1 and VRN-H2 loci. All lines had the “winter” allele at HvBM5A, the candidate gene for the VRN-H1 locus. Out of 54 lines, 46 had the “winter” allele at VRN-H2, where the ZCCT-H gene cluster is the candidate, classifying them as “winter” genotypes. Winter and facultative phenotypes were compared to winter and facultative genotypes. The phenotype was accurately predicted from genotype 94% of the time. Possible reasons for the <100% accuracy include residual heterogeneity and difficulty in classifying the growth habit of some lines under spring-sown conditions.