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Root exudates of the invasive <i>Solidago canadensis</i> and the cereal crop <i>Sorghum bicolor</i> (L.) Moench cv. ‘Hybridsorgo’ were tested for allelopathic interactions against native and invasive plant species in a controlled environment. After the surface was sterilized, the seeds of two invasive species (<i>Bromus sterilis</i> and <i>Veronica persica</i>) and two native species (<i>Youngia japonica</i> and <i>Rumex acetosa</i>) were germinated and transplanted into the soil (1:1 mixture of coco peat and sand) that had been conditioned for one month by the cultivation of <i>Solidago canadensis</i> and <i>Sorghum bicolor</i>, both in combination or as unplanted controls. After an additional eight weeks of growth, morphometric measurements of the shoot and root, including foliar characteristics and above- and below-ground biomass accumulation, were performed. The results revealed significant inhibitory effects of root exudates released by <i>Sorghum bicolor</i> and <i>Solidago canadensis</i> on native species’ productivity and physiology. The invasive species exhibited variable growth responses, with <i>Veronica persica</i> showing reduced shoot and root expansion, but <i>Bromus sterilis</i> revealed increased shoot and root biomass allocation and nutrition under the exudate treatments. Exudates from <i>Solidago canadensis</i> and <i>Sorghum bicolor</i> together showed synergistic negative effects on native species, while they promoted growth and nutrition in <i>Veronica persica</i>. Taken together, the differential species responses indicate that the tested native species were more sensitive to the allelopathic compounds than the invasive species, which is in line with the theory of novel weapons. The legacy effects of root exudates of both <i>Sorghum bicolor</i> and <i>Solidago canadensis</i> could promote invasive establishment through imposing allelochemical interference competition against native plant species. Understanding the specific allelopathic mechanisms may help with the development of integrated strategies for managing invasive species.