Japanese knotweed ( Fallopia japonica ) is a highly invasive species that has become a serious problem in riparian zones and along road and railroad right-of-ways in North America and Europe. Once established, it forms solid colonies choking out other herbaceous vegetation, displacing native species, negatively affecting wildlife, and altering hydrological processes. We evaluated the ability of 6 native species mixtures to prevent recolonization by Japanese knotweed at a site receiving either 1 or 2 yr of glyphosate applications and mowing to suppress existing Japanese knotweed stands. One year of spraying and mowing was not sufficient to adequately suppress Japanese knotweed. By 37 months after sowing, only the multi-species riparian buffer mixture (RBM) had plant cover 20%, whereas cover for all other mixtures was Elymus virginicus ) and prairie cordgrass ( Spartina pectinata ). Percent cover for both mixtures was 80% at 25 months after sowing and ≥50% after 37 months. Two years of Japanese knotweed suppression was necessary before native species mixtures could successfully compete against invasive recolonization.