Invasive plants are a major threat to biodiversity and may adversely affect food security. Clonal integration enables the sharing of resources between connected ramets and can enhance plant performance in many invasive species. However, few studies have examined the role of clonal integration when weeds are exposed to plant growth regulators (PGRs). PGRs are used extensively in agriculture and may affect nearby weeds through soil leaching, erosion and runoff. Our aim was to investigate the effects of clonal integration on growth in a noxious weed, Alternanthera philoxeroides (alligator weed), in response to two PGRs frequently used in agriculture, gibberellins (GAs) and paclobutrazol (PAC). Ramets of A. philoxeroides were propagated in the greenhouse, and treated with PGRs. PGRs were applied to the older ramets (i.e. ‘basal’ part), with half of the plants having the stems between the apical (younger) and basal parts left connected, while the remaining plants had the stems between the two parts severed. Following the growing period, plants were measured for growth traits. We found that GA and PAC had contrasting effects on plant growth. GA significantly promoted above-ground growth of the apical ramets via clonal integration. Alternatively, PAC inhibited above-ground growth in the basal and apical parts, and enhanced below-ground growth of the basal and apical ramets through clonal integration. Our results highlight how clonal integration can promote growth in A. philoxeroides following the application of PGRs, which is likely an important mechanism for this species to invade new environments.