The spread of invasive weed species Russian (Acroptilon repens) and spotted knapweed (Centaurea maculosa) are wreaking havoc upon native plant ecosystems in the western US at tremendous environmental and economic costs. Their successful spread has been attributed to the exudation of allelopathic chemicals by their roots into surrounding soil. These chemicals are phytotoxic to native plant species. The toxicity of these allelochemicals is a function of their bioavailability in the soil solution which is regulated by soil sorption (retention) processes. Very little is known about the sorption of these allelochemicals in soil, specifically, under what soil conditions (soil constituents (i.e., organic matter, clays, and oxides) and pH) do these chemicals maximally sorb? The work presented in this paper will seek to answer these questions. Our objective is to identify the soil conditions that optimally sorb the allelochemicals produced by the aforementioned weeds and use this knowledge to develop a preventative management scheme that will limit the spread of these weeds. Understanding the conditions resulting in optimum sorption – or minimal bioavailability – of these allelochemicals could provide a means to arrest the spread of these weeds. The idea is to amend an infested site with the agent(s) found to maximize sorption. Ideally, this would eliminate the competitive edge provided by the release of phytotoxic chemicals. Ultimately, by combining weed maps with soil maps, areas that should receive amendments can be identified thus mitigating the spread of these weed species.