The aim of this study was to evaluate the efficacy of new biological agents used in organic farming of evening primrose, in termsof improving the quality and yield of seeds. Field experiments were conducted in 2008-2010 and under different growing conditions: in sandy clay soil in drought (not watered) or under optimum condition where soil and plants were irrigated when needed. Biological compounds, exhibiting different mechanisms of action (Tytanit, Biojodis, Physe, EM) were applied to seeds, leaves and soil. Their impact on the inflorescent architecture, seed yield and fat content and the content of GLA in the oil extracted from seeds was determined. Studies have shown that the cultivation conditions and used bio-compounds influenced the growth and development of plants and seed maturation. The growing conditions largely determined the yield of seeds. In optimum conditions (optimal irrigation) the yield was more than twice higher than in drought (not watered).The tested bio-compounds were most effective in improving of the evening primrose growth in extreme conditions (not irrigated soil). The most beneficial results and a significant increase in seed yield was obtained in drought (not watered) after their foliar treatment with biostimulator Tytanit or after soil application of EM. The seeds obtained from the treated plants contained 2.9% more of oil than in control. Content of y-linolenic acid in oil was slightly higher in seeds obtained from the treated plants than in control, but these differences were not statistically significant.