Population characteristics of Spartina argentinensis after fire were analyzed. Field experiments were done in temporary flooded tall grassland, dominated by S. argentinensis at the Reserva Federico Wildermuth (Argentina), on burnt and non-burnt plots. The following variables were analyzed: soil seed bank, potential and real establishment of seedlings and the effect of fire on them, percentage of tillers that continue growing after fire, emergence and survival of tillers, number of tillers that differentiated panicles, and production and predation of propagules. Plants resprouting after fire produced a larger number of tillers with greater tiller emergence, recruitment, and survival than tillers of those of the non-burnt plants. The proportion of tillers with panicles and number of full spikelets per plant was greater in burnt plants than in non-burnt plants, but individuals caryopses unitary weight as well as germination percentage and viability were not affected by fire. Caryopses were severely predated and they did not build up a permanent seed bank. In spite of the high output of caryopses, seedling establishment was almost negligible under most circumstances. Fire and environmental conditions provided very limited “windows of opportunity” for seedlings recruitment. Asexual reproduction was the main process of population maintenance and growth, and fire triggers off the output and eventual establishment of sexual propagules.