The agency has taken over the business after the Flowers & Plants Association moved from Fallon in a bid to focus on sales in the north of England.
CheethamBell JWT's work will continue the strategy developed by Fallon, which aims to persuade women who rarely receive flowers from their unromantic partners to go out and buy their own. It introduced the strapline: "Why wait? Buy your own. The creative work won a silver award at the Campaign Press Awards last year.
Laurence Green, a partner at Fallon, said: "The budget and geography made using a London agency redundant. The campaign idea we produced worked very hard for them, and they are using it with our blessing."
Media will be handled by MediaCom North. A new campaign, running across TV and outdoor, is set to break on 9 September.
Veronica Richardson, the chief executive of the Flowers & Plants Association, said: "It is imperative that the agency for this campaign has comprehensive experience and knowledge of local consumers. CheethamBell JWT has this in abundance, combined with an impressive creative reputation across the board."