The appointment of Tonic, founded last December by the former Vizeum directors Geoff Seeley and Tim Elton, follows Yeo Valley's choice of Banks Hoggins O'Shea/FCB to handle creative work.
Tonic will advise on a media strategy, starting with a test campaign this summer in the South-East. Creative work is built around the strapline "in a world gone mad, it's sanely delicious" to support specific Yeo Valley products as well as the corporate brand.
Ben Cull, the marketing director at Yeo Valley Organic, said: "We want to test a number of creative executions, as well as assess the effectiveness of different media. Tonic is advising us on planning and strategy and will also be helping to ensure our media buying is as effective as possible."
Yeo Valley Organic uses the Bristol-based Taylor & Taylor for its media buying. It used Delaney Lund Knox Warren & Partners and MediaVest for its first ad campaign in 2000.