Results are presented from artificial freezing tests comparing young controlled crossed progenies from the southern seed orchard at Lyngdal (58° N) with open‐pollinated progenies from the same mother trees standing in the northern natural forest (63°‐66°N). The seed orchard material was more damaged by frost during cold acclimation. This effect was persistent for more than one growing season. Different photoperiodic treatments imposed on the progenies the first year did not affect the hardiness level in the same material three years later. The results imply that the seed orchard material has been genetically altered to perform like more southern ecotypes than the progenies form the forest. Possible causes of the present results are discussed in relation to four alternative hypotheses. In two of these it is postulated that the parental environment in the seed orchard could alter the genotypic performance of the progenies.