AbstractWhen grown in Scotland over three years, eight cultivars of diverse origin showed considerable variation in the date on which the first fruit ripened. The date was determined by a combination of date of first flower opening and number of days from flowering to ripening. Genotype X environment interactions were important for both components, but especially for the second, where they could be attributed to heterogeneity of regressions against the environmental means. Accumulated heat units accounted for intercultivar differences in number of days from flowering to ripening: cultivars required similar numbers of heat units in each season and there were no interaction effects. Accumulated heat units were not associated with flowering dates. The first to ripen was the hexaploid American cultivar Chehalem (57.4 days from a base date), which was obtained by crossing an octoploid form of Rubus ursinus with R. procera. This was followed by Bedford Giant (65.3 days), which is a hexaploid derived from a tetraploid raspberry X blackberry cross.