Flexible canopies bend and oscillate in both the in-line and cross-flow directions due to periodic forcing associated with vortex shedding. The resultant plant motion impacts the vegetation wake structure and, thus, the rate of lateral dispersion in these environments. Despite significant improvements in our understanding of dispersion in rigid canopies, a reliable framework to predict mixing in oscillating canopies is still lacking. This research demonstrates how plant oscillation can profoundly impact rates of lateral mixing in steady flows. The lateral dispersion coefficients were evaluated experimentally, using photographs of injected dye plumes within two types of emergent flexible model vegetation. Results revealed a significant increase in the rates of lateral dispersion (by up to 45%) due to the plant oscillation. A predictive model, based on a redefined vegetation density that incorporates the impact of plant oscillation, was developed that can accurately predict dispersion in emergent canopies. A quantitative prediction of dispersion in oscillating flexible vegetation is a significant step toward a more accurate description of material transport in aquatic environments.