Mary Spiller is one of only 100 holders of the Associateship of Honour. She studied under Beatrix Havergal, who set up the Waterperry School of Horticulture for Ladies in Oxfordshire in the 1930s, and joined the staff in 1944. She has worked there non-stop since 1963 apart from a stint presenting Gardeners' World in the 1980s.
She said: "For me there are two really exciting things to do - grow plants and help other people to grow and love plants."
She received her award from TV's Roy Lancaster at the RHS Hampton Court Palace Flower Show.