This work aimed to study the seasonal impact on the pollutant removal efficiency of constructed wetland (CW) units that treat domestic wastewater in the region of Rabat, Morocco. In this context, four vertical flow-constructed wetlands (VFCWs) were investigated for one year. Each CW unit has a surface area of 1 m² and a depth of 60 cm. The difference between the units is the vegetation. The experiments were conducted on a laboratory scale and outdoors to investigate the direct effect of climate. The purpose of this study was to investigate the performance of CWs with two different plant species (Phragmites australis and Arundo Donax) and plant arrangements (monoculture and polyculture). Since the region of Rabat has a semiarid climate, plants that behave during seasonal changes were explored. The elimination of organic matter showed seasonal variation in the CW systems, with higher rates occurring during the hot season and lower rates occurring during the cold season. The planted system outperformed the unplanted system, and the polyculture system was the most effective, reaching removal rates of 99.47%, 99.58%, and 85.64% for COD, BOD5, and TSS, respectively, in the summer season where the temperature reached its maximum, promoting plant growth as well as microbial activity. The results showed that the VFCWs used in this study are a successful technology for regions that are cost-effective and require little energy.