Canna indica L. is an upright perennial rhizomatous herb, and Schoenoplectus validus (Vahl) A. Löve and D. Löve is a tall, perennial, herbaceous sedge. The nutrient uptake kinetics of C. indica and S. validus were investigated using the modified depletion method after plants were grown for 4 weeks in simulated secondary-treated wastewater. The maximum uptake rate (Imax) and Michaelis–Menten constant (Km) were estimated by iterative curve fitting. The Imax for NH4N (623 μmol g−1 dry root weight h−1) was significantly higher than that for NO3N (338 μmol g−1 dry root weight h−1) in S. validus. In contrast, no difference was observed in C. indica. The Imax values for NO3N and NH4N were higher in S. validus than in C. indica. A significantly lower Km was detected for NO3N uptake in C. indica (385 μmol L−1) compared to that in S. validus (1908 μmol L−1). The Imax for PO4P did not differ between the plant species. The Km for PO4P was significantly higher in C. indica (157 μmol L−1) than in S. validus (60 μmol L−1). In conclusion, we found that S. validus preferred NH4N over NO3N, had greater capacity for N uptake and higher affinity for PO4P, but C. indica had greater affinity for NO3N. Nutrient uptake capacity is likely related to habitat preference, and is influenced by the structure of roots and rhizomes.