Creative director Therese Lang said: "I'm thrilled this is happening again ... it's needed for designers. It's exciting because there is a designer brief on sustainability and no other garden festival has done that yet. It will be more popularist and not so intellectual."
She added: "There's a huge amount of money behind it from a private investor and a huge bank."
Lang said a proposed revival of the Westonbirt event in Northamptonshire fell down 18 months ago due to a lack of facilities.
Property developer Clive Farrell, who bought 11ha of the RNRS garden in 2003, is to set up Butterfly World on the site. Lang said: "In 2010, the ring of gardens will turn into a rainforest dome full of butterflies. Then Future Gardens becomes part of Butterfly World."
Designs are being sought for 12 garden sites at the show. A bursary scheme offers designers a maximum budget of £25,000 to cover construction and materials.
The deadline for submissions for the 2009 event is 14 July 2008.
Call 01373 812223 for details.