HW has learnt that the RHS has asked entrants to July's Tatton Park national flower bed competition to reduce bedding planting to become just a third of schemes.
The society will give £2,000 to each of the 14 councils that have entered to plant two-thirds permanent planting on their displays.
Shows development director Bob Sweet said: "A number of local authorities said they can't afford to plant bedding any more so want more permanent plants in their flower beds.
However, bedding grower representatives who did not know about the move said they were "confused" and "intrigued" by the decision.
Since the show began in 1999 exhibits have had up to 20 per cent "dot" planting of perennials. The competition, which will run this year on 20-24 July, usually features around 20 local authorities and has always been Britain's biggest stage for bedding. Seventeen councils entered in 2010.
Sweet said: "We are giving local authorities a small grant and asking them to plant beds with a mixture of permanent and bedding plants, which reflects the economic circumstances in which they're working."
An RHS representative added: "This reflects how councils are moving away from bedding towards permanent planting. In this (economic) climate it's hard for them to justify keeping the glasshouse going over winter." He said the criteria was now to plant one-third bedding and two-thirds perennials.
Bedding plant and seed supplier Ball Colegrave pulled out of sponsoring the event last year.
Reaction from the bedding plant industry
Sarah Fairhurst, chairman, British Protected Ornamentals Association
"If it is called the National Bedding Plant Competition I'm a little confused about the RHS putting permanent planting in it. It doesn't seem to tie in."
Ian Riggs, marketing committee head, British Protected Ornamentals Association
"Why doesn't the RHS give a grant for bedding? Why does the RHS want to promote perennials instead of bedding? I'm intrigued why the RHS is supporting one grower industry and not another."