One year-old Pinus halepensis seedlings, grown in peat-vermiculite-pine bark mix in 200 cm3 containers, were moved to a growth chamber and submitted to a progressive decrease of temperature and photoperiod for three months. Morphological parameters and nutrient and non-structural carbohydrate content were measured. Root growth potential, freezing and drought resistance tests were assessed. Although height growth stopped when the minimum temperature fell below 9°C, shoot dry weight increased further. Needle potassium concentration and K/N ratio increased progressively and significantly throughout the trial. This may be attributed to potassium accumulation. As height growth stopped, physiological changes were detected in shoot nitrogen and soluble sugar concentrations, root activity and hydraulic conductance maintenance. Nevertheless, cold and drought resistance tests, as well as root regeneration potential, did not reveal any sign of plant stress tolerance until the minimum temperature decreased to 8°C and photoperiod to 9 h. This latter temperature may be considered to be the threshold for Pinus halepensis to accumulate the required chilling hours that make seedlings suitable for afforestation purposes. At least, more than 330 chilling hours (< 8°C) are required to reach a minimum level of stress hardiness. The Fv/Fm chlorophyll fluorescence ratio, measured just one day after the freezing test, provides a good estimate of plant frost tolerance.