Six provenances of bothPseudotsuga menziesii(Mirb.) Franco andPinus contortaDougl. from a range of locations in the interior of British Columbia between latitudes 49° and 58° were grown for 80 days in controlled environment chambers programmed to provide daylengths comparable with those at either latitude 48°, or latitude 58°, during the period from mid‐June to early September. Neither shoot : root ratio nor whole plant dry weight ofP. menziesiiwere affected by photoperiod. However,P. contortaseedlings, which unlikeP. menziesiiset bud during the experiment, had a greater dry weight and a higher shoot:root ratio (p<0.05) under longer daylengths. The results appear relevant to the interpretation of effects of cross‐latitudinal provenance transfer on plantation productivity.