The cultivation of wild greens under the conventional culture system has been increasing in Korea, but the production cost is high and the quality of the products’ flavor and aroma is not as good as that of uncultivated wild plants. Thus, cultivation of wild greens in a forest farming system is an attractive alternative to wild harvesting, due to its much lower production cost compared with conventional cultivation, and its provision of a second income to the landowner. Yet little is known about the conditions that would maximize the growth of wild greens in a forest farming system. Thus, this study was conducted to evaluate the optimal conditions that would maximize the yield of Ligularia fischeri (Ledeb.) Turcz., which is being cultivated in three forest farming systems in Korea. After the fibrous roots of L. fischeri were planted in hardwood forests, the environmental conditions therein were measured, including the relative light intensity, soil moisture content, and plant growth characteristics such as the survival rate, total number of leaves, and leaf width. The results showed that the light intensity and tree density in such sites were significantly correlated with the leaf growth. It is thus suggested that the 20–40% light transmittance that was measured in the open field is the optimal condition for the growth and yield of L. fischeri in a forest farming system. The results of this study can help formulate a management plan for when thinning practices should be performed, to establish a forest farming system and to maintain a suitable tree density for the cultivation of wild greens.