Photoperiod response in switchgrass (Panicum virgatum) is related to latitude of origin. Northern upland cultivars from the northern Great Plains generally have a long-day response, whereas southern upland cultivars may have a short-day or day neutral response. The objective was to determine if there was genetic variation for photoperiod response within cultivars with origins from natural populations from the northern Great Plains. Variation for photoperiod response was found among genotypes within the cultivars Summer and Sunburst in the greenhouse under non-growing season ambient daylengths.