This study investigated the nitrogen removal performance in wetland microcosms individually planted with different plant monocultures, including emergent, free-floating and submerged plants during ammonia removals, or large- and small-leaf free-floating plants during nitrate removal. For ammonia-dominated wastewater, both emergent (common reed) and free-floating (water hyacinth) plants in wetland microcosms achieved higher total nitrogen removals than a submerged plant (eelgrass) that significantly improved the microbial nitrifying performance. For nitrate-dominated wastewater, efficient nitrate removals in wetland microcosms planted with free-floating plant were achieved by both a full cover of water surface and the concentration of organic oxygen-consuming substances, which resulted in low dissolved oxygen levels and boosted microbial denitrification in wetland microcosms. FWS-CW developers and managers should thus pay close attention to the selection of wetland plant types and optimize their design to achieve optimum nitrogen removal performance.