The aim of this experiment was to determine the effects of three foliar biopreparations applied once or twice (growth stimulant Bio-algeen, fertilizer Herbagreen Basic, and Effective Microorganisms in the form of EM Farming spray) on yield and quality of herbal raw material of organically grown garden thyme (Thymus vulgaris). It was proved that the Bio-algeen had an effect on increasing thyme productivity, whereas Effective Microorganisms had no impact at all on herb yield. The beneficial action of biopreparations was more evident under favorable hydrothermal conditions over the study period than under unfavorable conditions. The biopreparations stimulated an increase in the essential oil content in the thyme herb. Bio-algeen, especially when applied twice, had the greatest positive influence on the quality of raw material, Effective Microorganisms were found to have a smaller effect (positive and negative), whereas Herbagreen Basic had positive effect on thyme yield and essential oil content. The effect of Bio-algeen, and to a lesser extent that of Effective Microorganisms, on the content of natural antioxidants (phenolic acids, polyphenols) in the thyme raw material and, moreover, its impact on free radical scavenging and antioxidant activity should be considered to be a particularly valuable finding. Due to application of the Bio-algeen, herbal raw material characterized by the best health-promoting parameters can be obtained.