We studied sessile oak (Quercus petraea) growing on six dry sites to understand adaptability responses to drought stress. Pedunculate oak (Quercus robur) on a moderately dry site was tested in parallel. We analyzed accessions from mostly dry sites that were less sensitive to soil drought and found that the growth performance ranking was not the same before and after treatment. We used phenological plasticity approaches to study seed development and plant development before and after drought: the treatments included stem length, root length, and collar diameter, as well as dry above- and below-ground biomass performance. Additionally, after drought treatment, osmolytes and root surface were tested in Q. petraea. According to the analyses and results, the ranked sites did not maintain their ranking status, with Q. petraea exhibiting different rates of growth during each developmental stage from seed development until the end of the treatment of plant material. The smallest seeds came from the driest site, which may indicate more adaptability to drought stress. After drought treatment, large differences were found between the dry biomass performance, stem length, root length, and collar diameter of oaks grown on different sites. The osmolality of Q. petraea on most of the dry sites was higher under the reduced treatment than under the optimal treatment, but not significantly. After drought treatment, all accessions – and especially those from the driest site – showed large differences in growth performance between the treatments. The relationship between seed weight and seedling development before and after drought treatment differed according to the developmental stage.