Loss of plant species diversity in wetlands has been linked to high nutrient conditions. In particular, Typha spp. are known to form monotypic stands in fertile wetland systems. In this study marsh mesocosms were used to study the effect of nitrogen (N), phosphorus (P) and nitrogen and phosphorus (N and P) additions on density, biomass and nutrient dynamics of Typha latifolia L. and the sedge Schoenoplectus tabernaemontani (C.C. Gmel) Palla (a.k.a. Scirpus validus Vahl.) grown in size- and density-symmetric and in size- and density-asymmetric mixtures. Dynamics of Typha and Schoenoplectus mixtures were also estimated along a nutrient gradient in a created wetland. Typha responded with increased growth to higher nutrient conditions more than Schoenoplectus in the first year, but Schoenoplectus responded more than Typha in the second year when nutrient additions were stopped. Typha grew better compared to the control with the addition of nitrogen and phosphorus in both the asymmetric and symmetric mixtures. Nitrogen or phosphorus, when added alone, did not increase the growth of Typha when it was grown with Schoenoplectus. The presence of a one-year-old stand of Schoenoplectus reduced aboveground growth of introduced Typha in both high- and low-nutrient conditions. In a created marsh Typha biomass decreased and Schoenoplectus biomass increased along a gradient of decreasing nutrient concentrations. N:P ratios in aboveground tissues of both plant species were less than 14:1 (by weight) suggesting N limitation. Plant tissue ratios, however, were close to the Redfield ratio of 7.2:1, suggesting no nutrient limitation.