Due to their good early vigour, Swiss maize landraces have been used extensively to develop the Flint Pool of European hybrid-breeding programmes. However, the basis of good early vigour, especially under cool conditions, has not been elucidated. Of 166 pre-screened Swiss maize landraces, 17 contrasting accessions were tested together with two control accessions, a German landrace and a modern hybrid cultivar with proven good early vigour, at sites in the midlands and the foothills of the Alps in Switzerland. To investigate early vigour, photosynthesis, leaf greenness and plant growth were recorded. Compared to the modern standard hybrid cultivar, northern accessions showed superior early vigour under cold stress in the field for all traits examined in these experiments, whereas these traits were much less pronounced in southern accessions. In particular, some accessions from the Rhine valley seem to be promising sources of early vigour for use in breeding programmes. These findings support the hypothesis that long-term selection resulted in the adaptation of maize landraces to their local environment. Compared to the phylogenetic tree, it is evident that accessions with superior early vigour are related to each other and originated in the Rhine valley.