The aim of this study was to determine the accumulation of antioxidants at аn early stage of development of organs of P. incarnata L. plants grown in greenhouses (medicinal aromatic plants were used for comparison), as well as to evaluate the effect of biostimulant Albit. The use of amperometric and biochemical methods made it possible to measure and evaluate the total antioxidant content in aqueous extracts of leaves of aromatic plants with sedative effects compared to aqueous extracts of P. incarnata L. leaves. The latter are characterized by a lower level of antioxidant accumulation. Seed treatment with biostimulant Albit and foliar treatment of aerial parts of the P. incarnata L. plant increased the total antioxidant content and the content of carotenoids, chlorophylls a and b, and the yield of aerial parts of the plant by 10–15%. The findings suggest that the P. incarnata L. plants grown in greenhouses can be used to create antioxidant herbal remedies.