The field experiment was carried out on a private farm in Trębanów, Świętokrzyskie Province, in 2020–2022. The aim of the study was to determine the effect of selected biopreparations on the morphological traits of plants, the size and structure of yields, and the content and yield of Greek oregano essential oil. Natural biostimulants Stimplex (2 dm3 ha–1), Tecamin Max (1.5 dm3 ha–1), and Kendal (1 dm3 ha–1) were used in the study. The results demonstrated positive effects of the foliar application of the biostimulants on the morphological, performance, and quality parameters of Greek oregano. The most effective treatment was the application of the biostimulant containing extracts of Ascophyllum nodosum algae (Stimplex), followed by the preparation containing amino acids (Tecamin Max). They increased the plant growth rate, the number of lateral branches, and the raw material yield and had a positive effect on the content of essential oil. The size and quality of the Greek oregano yield also depended on the age of the plants and varied between the study years. Higher raw material and oil yields were obtained from two-year plantations. The drought in 2022 limited plant growth and resulted in a lower yield; nevertheless, the essential oil content in the herb increased in these conditions.