Greenhouse gas emissions significantly contribute to global warming, seriously threatening our ecosystem. Human civilisation is currently too dependent on fossil fuels and global energy resources that generate greenhouse gasses. A solution can be found in the sustainable development of renewable energy to reduce GHG (greenhouse gas emissions). Biogas production using various digestive materials represents an alternative to fossil fuels. Their replacement with methane gas, GHG emissions, and global warming are environmental factors encouraging the proliferation of the invasive plant species Fallopia japonica, commonly called Japanese Knotweed. This has been recognised as a significant threat to European biodiversity. Controlling this unwanted species is associated with high economic costs. A laboratory study, performed under controlled environmental conditions, was conducted on harvested stems and leaves of the Fallopia japonica plant using different digested matter (DM) to produce biogas energy. The presented study aimed to determine how different DM changed the levels of biogas produced and its methane content. Additionally, the plant material’s capability for regrowth at 37°C in a controlled environment following digestion was investigated. The results demonstrated that Fallopia japonica could be used to produce biogas with high methane concentration. However, the subsequent assessment did not demonstrate regeneration of Fallopia japonica following digestion