Three screening methods -Visual scoring (V), Relative Conductivity (C) and Fluorometry (F)- were used to study the genetic variation in cold hardiness among six populations of maritime pine (Pinus pinaster Ait.) comprising both Atlantic and Mediterranean origins. Freezing damage assessments were carried out in three organs - needles, stems and buds- in two seasons -spring and autumn-. We found high levels of genetic differentiation among populations for cold hardiness in autumn, but not in spring. Within-populations, differences were always significant (p < 0.05) no matter which organ or screening method was used. Measuring F was the fastest and most easily replicated method to estimate cold hardiness, and was as reliable as V and C for predicting the species performance. In autumn there was a positive correlation between the damage measured in all three types of organs assessed, whereas in spring correlation among organs was weak. We conclude that sampling date in spring has a crucial impact to detect genetic differences in maritime pine populations, whereas autumn sampling allows more stable comparisons. We also conclude that the Fluorometry method provides a more efficient and stable comparison of cold hardiness in maritime pine.