Technical Abstract: Increasing concentrations of greenhouse gases (GHG) including carbon dioxide, methane, and nitrous oxide are widely believed to be the main contributing factors leading to global climate change. The horticulture industry has the potential to improve GHG conditions through sequestering carbon (C) in urban landscapes. In order to determine effects of growth media on soil CO2 efflux, a study was conducted in which two common landscape species grown in containers using three different growing media: 1) Pine Bark, 2) Clean Chip Residual, or 3) Whole Tree; after one growing season they were outplanted into the field. Initial soil samples were collected for C content determinations. Automated Carbon Efflux Systems (ACES) were installed adjacent to three plants of each species in each media for continuously monitoring (24 hr d-1) of C lost via soil respiration and to determine media C sequestration potential. Increased soil C was primarily noted in the upper soil depth (0 - 15 cm), where PB was higher than the other media; a similar pattern was observed for the 15 – 30 cm depth although C values were much lower. Crape myrtle had higher soil CO2 efflux than magnolia possibly due to crape myrtle having a larger root system or faster growth rate. All media had different soil CO2 efflux values in crape myrtle (CCR was highest and WT lowest), while for magnolia PB was higher than the other media. Across both species, WT had lower efflux than PB and CCR possibly due to its higher wood content causing it to break down slower. Placing containerized plants into the landscape transfers a large amount of C belowground, suggesting that opportunities exist for the horticulture industry and homeowners to contribute positively to mitigating climate change via soil C sequestration. However, further investigation is needed to fully understand the impact of various growing media and ornamental species on soil CO2 emissions and the residence time of this C in soil when planted into urban and suburban landscapes.