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The ability of established crested wheatgrass (Agropyron cristatum) to suppress cheatgrass (Bromus tectorum) is well documented. Many studies examining the competition between these two species, usually do so at the seedling phase. We do not consider decreased performance between two seedlings as an appropriate use of the term “suppression” as it relates to weed management. We define cheatgrass suppression as an established perennial grass having a negative effect on the density of cheatgrass. This is seen with the familiar bare rings around a mature crested wheatgrass plant. We have also observed that in years of high precipitation, these rings of suppression reduce in diameter with cheatgrass growing proximate to crested wheatgrass plants with no apparent signs of “suppression”. We designed an experiment adding artificial precipitation at bi-monthly intervals (March-May) to replicated (9m2) crested wheatgrass stands (4.26 plants/m2) in order to measure suppression effects. We hypothesized that increased precipitation would decrease suppression. We measured the cheatgrass seed bank prior to the study and added seeds so that all treatments were equal. Treatments included adding additional 4.57cm precipitation (Treatment 1) and 1.52cm precipitation (Treatment 2). The natural precipitation (control plots) for that time period was 2.36cm. We also eliminated crested wheatgrass (Glyphosate) from treatment 2 plots (Treatment 3). Treatment 1 had on average 101 cheatgrass plants/m2 compared to 8 cheatgrass/m2 in control plots. Treatment 2 plots had 23 cheatgrass/m2. Cheatgrass plants in treatment 3 (Crested removal) were significantly larger than others likely due to increased available soil nitrogen (14ppm vs. 5ppm). Overall we find the results support our hypothesis but acknowledge there are many other interacting factors. Suppression is seldom “complete” with cheatgrass seed banks ever present and awaiting a disturbance to gain dominance. Management to preserve perennial grass stands is critical as this research demonstrates the fragility of cheatgrass suppression.