Controlling invasive plant species is a vital task for habitat restoration. Reed canary grass (Phalaris arundinacea) is an invasive species that has extensively established in and threatens floodplain forests along the Upper Mississippi River. To explore the use of direct seeding to facilitate re-establishment of floodplain forest ecosystems along the Upper Mississippi River, we studied competition between reed canary grass and swamp white oak (Quercus bicolor) under greenhouse conditions. Shading decreased reed canary grass biomass and root:shoot ratio, but oak density did not affect reed canary grass growth and development. Shading increased reed canary grass seedling height. The presence of reed canary grass reduced oak biomass and seedling height but increased oak root:shoot ratio. Shading decreased oak biomass only in the high oak density treatment when reed canary grass was absent. In addition, oak biomass was greater in the high oak density treatment. These findings suggest that eradication of reed canary grass prior to seeding is necessary, and control efforts should continue after seeding to increase the possibility of restoring floodplain forest ecosystems along the Upper Mississippi River.