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Phenology in plants is closely related to the environmental features of their habitats, which can act as habitat filtering, clustering species with particular adaptations. On the other hand, aggregation of species can lead to competition between them, segregating their niches. We investigated if habitat filtering and interspecific competition influence phenological diversity in an assemblage of grass species in savanna grasslands of central Brazil. We conducted phenological observations, in 15-day intervals, of ten species of savanna grasses. We used circular statistics to ascertain the seasonality of the phenology and null models to estimate the phenological overlap between species. The reproductive period of grasses was seasonal and concentrated in the rainy season, corroborating the habitat filtering hypothesis; however, within the rainy season, the phenological niche overlap between species was less than expected at random. Flowering was more segregated than fruiting and seed dispersal. Although grasses have similar architectural feature and share similar above and underground niche, these results suggest that grasses are under competition pressure and this can result in phenological segregation, allowing coexistence between them.