Are practical gardening books losing out to the internet? His words prompted applause from some of the guests at the lunch, but eye rolling from others. Is there really a crisis in the world of horticultural advice? Our own self-help guru, Helen Yemm, has been offering muddy-booted, green-fingered advice to readers since 2001. She agrees there has been a shift. Hessayon has not got where he has by being wrong. He is a master of communication about gardening, and his books are still classics," she says. He knows what's going on. I can't speak about the books industry, but the whole temperature of what I do has changed. People who ask me questions are getting a lot of their information from the internet. They can see descriptions and pictures on demand. Also, gardening itself is changing so quickly, with different chemicals and new plants, that you can't be sure that a book is up-to-date. People now say 'I have read this and read that - which is right?' The change has been incredibly rapid - over the past two years, I would say. People are much more knowledgeable than they used to be. They are fed information from everywhere. That is the other argument - perhaps we have reached saturation point. All the books have been written. There are only so many times you can illustrate how to make a hanging basket or move a shrub. The explosion of video guides has been another factor, she adds. YouTube is littered with people dividing dahlias. Some are rubbish, of course, but others - such as Sarah Raven's - are excellent. As with cooking, it is helpful to see things being done. Industry figures suggest that Hessayon has a point. As editor of The Bookseller, Philip Jones has a good overview of the market, and can see gardening in the context of a shifting print economy. "There's definitely been a shift in the reference market from printed books to online resource: and in general this has been lost business, not money transferred to digital," he says. The problem for publishers is that, unlike with the fiction ebook market, they've largely failed to come up with a commercial model that works online. The bigger brands such as Encyclopaedia Britannica, and the Lonely Planet and Rough Guides, are now starting to row with this digital tide. "Not all reference markets are equally affected," he adds. Gardening looks tough, as is anything travel related. But cooking is still holding it own. Publishers must hope that the digital revolution will roll from the table to the allotment. It seems likely that the garden experts of tomorrow will be launched from tablets and smartphones, rather than books. Still, with more than 50 million books in circulation, it is unlikely we have heard the last of Dr D G Hessayon either. 'Indoor Plant and Flower Expert' by Dr DG Hessayon (Expert Books, £10.99) is available from the Telegraph Bookshop for £10.99 + £1.35 p&p. To order call 0844 871 1514 or visit Telegraph Books