Abstract: The purpose of this study was to determine cardinal temperatures of germination in three medicinal plants include medicinal pumpkin, borago and black cumin. Wide ranges of temperatures (5, 10, 15, 20, 25, 30, 35, 40 and 45°C) were used. A segmented regression model was used to determine base (Tb,), optimum (T0) and ceiling, (Tc) temperatures for germination. Tb was estimated as 5.9°C for medicinal pumpkin, 5°C for borago and 5°C for black cumin. T0 was estimated as 37.7°C for medicinal pumpkin, 29.9°C for borago and 28.6°C for black cumin and Tc was estimated 45°C for medicinal pumpkin, 39.9°C for borago and 35°C for black cumin. This information can be used in evaluation of new areas suitable for introduction of these species and optimization sowing management. In addition, it can be used to develop management models for prediction of timing of crop developmental processes.