Exposure to ambient PM2.5 poses serious threats to human health. In such cases, the presence of green roofs (GRs) and green walls (GWs) has several environmental benefits, including the capture of pollutants. Choosing appropriate designs of GWs and GRs to improve urban air quality is challenging because their performances depend on their constituent species and environmental characteristics of the particular locality. Capture of PM2.5 by different plant species of GRs and GWs has been measured only on monocultures. The impact of planting different species together (polycultures) on capturing PM2.5 remains unexplored. This paper aims to evaluate the impact of biodiverse GRs and GWs on PM2.5 capture. Seven species were analyzed as polycultures: Sedum album, Lampranthus spectabillis, Sedum spurium P, Lavandula angustifolia, Erigeron karvinskianus, Aptenia cordifolia, and Sedum palmeri. PM2.5 capture was measured by two methods: gravimetric determination and decay curve. Gravimetric results suggest that higher the biodiversity of plants in GRs and GWs, higher the PM2.5 capture, particularly for species with relatively low capture when used as monocultures. The ability to capture PM2.5 is dependent on the plant species, relative position of plants within the polyculture, and horizontal (GRs) or vertical (GWs) layout. Decay method results suggest that polycultures could be more effective in long-term reduction of high PM2.5 concentrations.