Limiting the negative effects of an invasive species, such as Reynoutria japonica, has become a challenge for scientists and a necessity for managers. Ecologically relevant, technically feasible, and sustainable control methods must be created to reduce the development or spread of R. japonica in ecosystems. The objective of our study was to investigate how monthly mowing in association with plant competition affects the development of R. japonica over a three-year field experiment. Among the plant traits measured, the height growth of R. japonica was the most affected; it was strongly reduced in the presence of competing plants. Combined mowing and competition with restoration plants negatively affected the growth diameter of R. japonica. Most competitive sown species were well established and complementary in limiting the development of R. japonica. The plant communities showed interannual dynamics in which R. japonica declined progressively. The restoration methodology adopted in this study allows managers to make appropriate decisions to reduce the impact of R. japonica on ecosystems.