He bred 70-80 roses varieties over the past 20 years after being able to concentrate on breeding following the sale of Harkness Garden Centre to Wyevale in 1996.
His brother Philip said Robert's major contribution to the industry was his "engaging personality and skill with words to take the roses around Europe, the USA, Australia and New Zealand and let other people share our pleasure of them".
Two of Robert's best-known varieties were Prince of Wales and Fellowship, which won many top awards around the world. The firm will continue with redistributed responsibility.
British Association of Rose Breeders general manager Ian Kennedy said: "The world of roses is a poorer place without his presence."
Robert's funeral was on 16 November at Harwood Park Crematorium in Stevenage.