This study investigates the potential for green roofs to support pollinator diversity and abundance in urban ecosystems through the altered floral phenology and floral abundance of plants. I compare floral phenology and the floral abundance of green roof plants to plants grown at grade on the Front Range in Fort Collins, Colorado, and how these changes may affect pollinator biodiversity in urban ecosystems. I employed an independent block design, with one green roof and one ground-level garden, approximately 120 meters apart, with replicate plants of 4 species at each garden. I found the abundance of flowers to be variable, depending on the plant species. However, all species of plants tested bloomed earlier when grown on the green roof than when grown at grade. We found pollinator abundance and diversity to be low at both the green roof and at grade. Nectar quantity and quality are diverse across a landscape and affect the health and behavior of some pollinators. I evaluated nectar volume and nectar sugar concentration between plant replicates grown on a green roof and grown at grade. Volume was measured in situ and sugar concentration was measured both in situ using a refractometer and, in a laboratory, using UPLC-RI. We found that there was no clear difference between nectar volumes of plants grown on the green roof and at grade while nectar sugar concentrations were generally higher in green roof plants.