Transport for London has installed sponsorship signs on a traffic island at the junction of Blackfriars Road and Southwark Street.
In their submission to Southwark Council planners, advertising firm Marketing Force said that the new billboards would "promote TfL's support of local businesses".
Planning officers granted advertisement consent for the scheme last month.
In recent years the flowerbed has been enhanced by the work of local guerrilla gardeners at no cost to TfL.
The traffic island will disappear in the next few years when the road layout is altered to accommodate the new One Blackfriars skyscraper development.