The author's new book, The Orchid Expert - to be published by Transworld early next year - could be his last.
He said: "Now that retirement is approaching, I felt it was time to give my favourite flower the 'Expert' treatment in order to remove some of its mystery. (Many orchids) are described, together with names of suppliers, for people who want to treat orchid growing as a hobby."
Hessayon had his first Gardening Expert guide published in 1959 and he has since sold around 50 million books.
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