Only two people are believed to have been knighted for services to ornamental horticulture in the past century - Sir Harry Veitch in 1912 and Sir Harold Hillier in 1983.
Charles Notcutt, who retired this year after 50 years in the industry, emerged as frontrunner for a knighthood in an industry poll.
Eden Project founder Tim Smit, Beth Chatto and Roy Lancaster were all mentioned in a HW poll.
Hillier chairman Robert Hillier said: "My father received his knighthood for services to horticulture and charity and there have only been two awarded in 100 years. It's unfortunate horticulture is not recognised more."
Lord Heseltine has said it was difficult to force through the knighthood of Sir Harold in 1983 because civil servants preferred to recommend an agriculturalist rather than a horticulturist for a title.
Former RHS president Sir Richard Carew-Pole and bulb grower Lord Taylor of Holbeach have titles for charitable and political work