The adult genet sex ratio of a wild population of the dioecious woody shrub Lindera benzoin (spicebush) in Maryland has shown a persistent female-bias over a time span of over 17 years. Female-biased sex ratios are relatively rare in dioecious plants, and are not easily explained by costs of reproduction, which are often higher in females. In fact, data from reproductive adults in this population showed modular growth favoring males, which led to questions concerning the source of female-bias. Using seeds collected from 20 maternal plants in 1992, a garden study was conducted from 1993–2003 in which periodic flowering censuses were conducted, and plant size parameters were recorded. The plants were grown in a relatively tightly packed array which likely forced early intraspecific competition. The results suggested that L. benzoin females may compensate for differential costs of reproduction via larger initial seed size and early growth rate, but that sexual dimorphism in such a highly competitive scenario can favor males even more dramatically than in typical field conditions. Despite larger early size and faster growth in female seedlings, males showed clear advantages over females in the post-reproductive period and mortality was much higher in female genets. Sex ratios were close to the same level of female bias seen in the wild population around the time of initial flowering, but trended toward maleness as post-reproductive stage genet mortality ensued. Explanations for the development and persistence of female bias include larger seedling size that may give females a competitive advantage over males in the pre-reproductive stage, which under certain circumstances may lead to greater survival of female seedlings. Variation among habitats in herbivory and other environmental factors that influence survival and sex expression could ameliorate the competitive advantage of males associated with their lower reproductive costs.