The contract covers RHS shows including Chelsea, Malvern, Hampton Court, BBC Gardeners' World Live and Tatton.
RHS members director Dan Wolfe said: "We're in ongoing discussions that are all very positive and will be decided very shortly, certainly within the next few weeks. We're happy with our relationship with the BBC. There's no better option to continue that relationship."
Channel 4 had a £250,000 contract for the shows from 1998 to 2000. The BBC paid £600,000 for a three-year deal in 2000, which was extended in 2005 and 2008. Wolfe said the current terms are confidential.