The agency was selected without a pitch by Interflora's marketing director, Michael Barringer, who was previously a senior marketer at Kodak.
Manning Gottlieb replaced Media Connection on the business. Its appointment follows the recent hiring of Walsh Trott Chick Smith to handle creative for Interflora.
Interflora plans to invest more heavily in advertising to raise awareness and build a more recognised consumer brand. Last year it spent £1.2 million, mostly through the Cambridge-based The Company. Its ads included a print campaign using the lines "tit elation" and "floral sex".
Walsh Trott's first large- scale campaign for Interflora is yet to break.
A significant element of the media planning and buying work is expected to include online activity.
Nick Manning, the chief executive of Manning Gottlieb, said: "Interflora isn't well known for its advertising but while it's something of a sleeping giant run on a trade association basis, its marketing team can turn it into a proper consumer brand."