Although polyploidy commonly occurs in angiosperms, not all polyploidization events lead to successful lineages, and environmental conditions could influence cytotype dynamics and polyploid success. Low soil nitrogen and/or phosphorus concentrations often limit ecosystem primary productivity, and changes in these nutrients might differentially favor some cytotypes over others, thereby influencing polyploid establishment. We grew diploid, established tetraploid, and neotetraploid Chamerion angustifolium (fireweed) in a greenhouse under low and high soil nitrogen and phosphorus conditions and different competition treatments and measured plant performance (height, biomass, flower and root-bud production) and insect damage responses. By comparing neotetraploids to established tetraploids, we were able to examine traits and responses that might directly arise from polyploidization before they are modified by natural selection and/or genetic drift. We found that (1) neopolyploids were the least likely to survive and flower and experienced the most herbivore damage regardless of nutrient conditions; (2) both neo- and established tetraploids had greater biomass and root-bud production under nutrient enriched conditions, whereas diploid biomass and root bud production was not significantly affected by nutrients; (3) intra-cytotype competition more negatively affected diploids and established tetraploids than it did neotetraploids. Following polyploidization, biomass and clonal growth might be more immediately affected by environmental nutrient availabilities than plant survival, flowering, and/or responses to herbivory, which could influence competitive dynamics. Specifically, polyploids might have competitive and colonizing advantages over diploids under nutrient enriched conditions favoring their establishment, although establishment may also depend upon the density and occurrences of other related cytotypes in a population.