In this study, changes in the pH of the nutrient medium were investigated after 35 days of cultivation of four white poplar genotypes (Populus alba L.). Four initial pH values of the substrate were tested: 3.0, 4.0, 5.5 and 7.0 buffered sodium citrate buffer, as well as a standard medium for micropropagation with pH 5.5 without the addition of citric acid (control) The medium was sterilized in a microwave oven. The results of the variance analysis indicate that the final pH of the medium after cultivation, as well as the difference between the final and the initial pH of the medium, was significantly influence of inital pH, as well as the interaction of the genotype × medium, differences between genotypes in their reaction to thewashed pH medium. On media with low initial pH was recorded positive, while the medium pH 7.0 was recorded negative change pH after cultivation. The results of the study indicate that changes in the pH of the medium during cultivation lead to a pH that is assumed to be optimal for their cultivation under in vitro conditions (cca. pH 5.5). The possibility of applying the obtained results in the improvement of the white poplar cultivation in vitro and the assessment of genotypes in melioration and phytooremediation projects is discussed.