Abstract. Coastal foredunes serve as a primary defence against storms and high water events. Dune morphology can determine how a dune functions as a barrier to storm impacts. Hummocky foredunes those with alongshore variability in dune crest elevation may have a greater potential for breaching during storm events compared to continuous foredune ridges. Initially scattered dune-building plants and species that grow slowly in the lateral direction have been implicated as causes of foredune hummockiness. Our goal in this work is to understand the causes and dynamics of hummocky foredunes by examining vegetation characteristics. Using a numerical model, we explore how the initial configuration of vegetation and vegetation growth characteristics set the development and evolution of hummocky coastal dunes including the maximum hummockiness of a given dune field. We find that given sufficient time and absent external forcing, hummocky foredunes anneal to form continuous dune ridges. We develop a predictive rule for the timescale of annealing that depends on initial plant dispersal and two parameters that control the lateral and vertical growth of vegetation, respectively. Our findings suggest that whether or not hummockiness will be maintained depends on the time scale of annealing relative to the recurrence interval of high water events that reset dune-building in the low areas between hummocks. This relation explains the tendency for foredunes to be hummocky along the southeast coast of the U.S. where lateral vegetation growth rates, and thus annealing times, are likely longer.