Head of shows development Bob Sweet said they were "difficult and controversial decisions" because some retailers earn their whole living selling these products.
Caterer Sodexho will now provide all UK-sourced food at Chelsea, Hampton Court and Tatton Park shows. The RHS will also provide separate bins for food waste and monitor waste skips as part of a new environmentally friendly drive at 2008 shows.
Cornstarch RHS carrier bags that exhibitors give customers will replace plastic bags by 2009 after a phasing-out period.
Sweet added: "We've got more to do. We're trying to take the industry with us. It's no good trying to fight (it). You will never succeed."
HTA director general David Gwy-ther said: There is undoubtedly greater interest in green ideas among gardeners but not yet huge evidence the consumer is greatly moved to change buying habits."