The content of essential oil and valerenic acids and the yield of roots were analyzed in valerian cultivar 'Polka' and strain no. 4 during the nine following phases: the beginning of vegetation, spring rosette, pedicel development, the beginning of flowering, full bloom, seed harvest, three weeks after the seed harvest, fall rosette, and after the first frost. The yield of valerian roots was different at the investigated phases and in years of cultivation, while tested genotypes produced similar root yields. The highest contents of essential oil and valerenic acids were obtained at different phases by the tested genotypes: strain no. 4 in full bloom (1.3% and 0.266%, respectively) and cultivar 'Polka' three weeks after seed harvest (1.25%) and during seed harvest (0.218%). The lowest contents of the investigated substances were detected at the beginning of growth and after the first frost in both genotypes. The obtained results revealed significant differences in essential oil and valerenic acids content, which depend on genotype, plant age, harvest time and the year of cultivation. The results suggest that higher amounts of valerenic acids could be obtained in the second year of cultivation over the period from full bloom (0.278%) to fall rosette phase (0.316%). [ABSTRACT FROM AUTHOR]