This study examined the growth promotion effects of selected water extracts on Peucedanum japonicum. As secondary considerations, the mineral nutrition levels were measured in both the extracts and the test plant. In addition, the levels of chlorophyll and the photosynthetic efficiency in the test plant were analyzed after the treatment of selected plant extracts. Finally, the total phenol, flavonoid contents, and DPPH (2,2′-diphenyl-1-picrylhydrazyl) radical scavenging activity in Peucedanum japonicum leaves were determined after the extract treatments. The shoot fresh weight of Peucedanum japonicum increased in response to all the extracts used, and in some cases increased at rates of 16–49% after extract treatments. Compared to the control, the photosynthetic efficiency and chlorophyll content of the Peucedanum japonicum plants did not vary significantly. In measuring the macro and microelements in the extracts, those with the highest levels were not necessarily the most effective growth promotors of Peucedanum japonicum plants. However, nutrition levels increased significantly in Peucedanum japonicum leaves after extract treatments. The total phenol contents in the Peucedanum japonicum leaves increased significantly when treated with the soybean stem extracts at 3%, Chinese chive extract at 0.5–3%, onion extract at 0.5%, or tomato extract at 3%. The total flavonoid contents in the Peucedanum japonicum leaves treated with the soybean leaf extracts at 0.5 to 3% increased by 23–36% compared to the control, but there were no differences with other extracts. Thus, the plant extracts tested in this study showed improved growth promotion, mineral contents, total phenol, total flavonoid contents, and DPPH radical scavenging activity.