AbstractIntermediate wheatgrass [Thinopyrum intermedium (Host) Barkworth and D.R. Dewey], bred for high grain yield, has become the first perennial grain in North America and is commercialized under the tradename Kernza. The expansion of this crop from the U.S. Midwest to areas with milder winters would require an understanding of its vernalization requirements for flowering and the availability of genetic diversity for this trait. The goal of this research was to determine the length of the cold period required for vernalization in Kernza intermediate wheatgrass. Two treatment factors (population and length of cold incubation period) were evaluated. Seeds from eight breeding populations from Kansas and Minnesota were evaluated in growth chambers at 5 °C and 10 h light for cold periods from 3 to 9 wk. The percentage of plants that flowered increased from 30 to 96% as the length of the cold incubation period increased from 3 to 7 wk following a sigmoid model. For most yield components, no changes were observed after 7 wk of cold incubation. There were no differences among populations for most traits and there was large within‐population phenotypic diversity. These results confirm that Kernza intermediate wheatgrass populations have moderate vernalization requirements. Further research is needed to confirm the feasibility of breeding Kernza with lower vernalization requirements.