Abstract: Eupatorium adenophorum is a serious grass weed, among the 16 most invasive plant species in China, widespread in pasture, agricultural land and forests in Southwest China. The potential allelopathic effects of this grass and mitigation strategies were investigated. Trifolium fragiferum, Lolium perenne and Medicago sativa, widely distributed in Liangshan, Sichuan, were used to investigate seed germination and seedling growth by comparing the extracts of composted and fresh E. adenophorum (extract of composted E. adenophorum, ECA; extract of fresh E. adenophorum, EFA) to determine the effects of E. adenophorum on pasture species and to develop a composting technique. Soaking seed in EFA depressed seed germination and young seedling growth to some extent; the effect was greater at higher concentrations. Seedling roots grew away from the EFA solution and some root tips blackened and died when growing in 100 mg/L EFA solution. After composting with a complex agent consisting of Pseudomonas putita sp. and Clostridium thermocellum sp., ECA increased the rate of seed germination by 21.1%, increased seedling height growth by 24.1% and seedling biomass by 22.5%. The results suggest the decomposition of toxicants in E. adenophorum during the composting process promoted seed germination and seedling growth. EFA inhibited hydrolysis of starch, protein and inositol phosphates in embryos,decreasing free amino acids, soluble sugars and soluble phosphorus in seedlings. Chlorophyll content and activities of roots and nitrate reductase were also decreased by EFA in contrast to ECA. Physiological changes in seedlings could be considered as a key reason for the inhibition of seed germination and seedling growth by EFA or promotion by ECA. Composting probably resulted in decomposition of toxins in E. adenophorum, offering a technique for managing the harmful effects of E. adenophorum while providing a large organic fertilizer resource for agriculture.