The timing of herbivory may have important consequences to components of plant fitness as well as the growth rate and persistence of plant populations. Specifically, this study examines whether the timing of herbivory by white-tailed deer (Odocoileus virginianus) affects the population dynamics of the long-lived herb, Trillium grandiflorum. This study combines results from a clipping experiment with demographic matrix modeling in four different T. grandiflorum populations to determine how both the frequency and timing of herbivory alter the population growth rate. Herbivory early, but not late in the season, increased the probability that reproductive plants fail to reproduce in the next year. Both early and late season herbivory resulted in a complete loss of reproductive success in the current year. Because the growth rates of these populations were sensitive to changes in the fate of reproductive plants, but insensitive to changes in annual fecundity, early season herbivory was more detrimental to population growth rates than late season herbivory. Plant persistence may depend as much on the timing of herbivory as it does its frequency.