Behind every book that is published lies a hinterland its author knows only too well, though readers will never be aware of it. This is a haunted landscape, populated by the ghosts of things written and excised, crisscrossed with paths that were thoroughly explored but came to a dead end, and alive with the faint echoes of stories that were eventually left untold. The further in time you get away from a book, the dimmer the details of its hinterland become, but some features remain more distinct than others. For example, I still regret deleting from my biography of Christopher Isherwood a detailed account of the circumcision he underwent in his grandparents’ house shortly before his fifteenth birthday in 1919. The reasons for the cut – if I may use the term in this context – had nothing to do with prudery or squeamishness, both of which would be very thoroughly challenged elsewhere in the narrative; it was simply that this was an episode that could be neatly and easily removed. Given that the tardy surgical procedure seems to have had no lasting psychological effect on Isherwood, it was difficult to maintain that it was essential to include a description of it in a book that was already too long. I had, however, been rather fond of it, since it made use of my hard-won knowledge of the family’s medical history and drew upon the hilariously periphrastic account of the operation given by Isherwood’s mother in her diary.

Radical surgery was also performed (to its benefit) on another of my books, Housman Country, my editor wielding his scalpel with relish while I stood nervously beside him in my scrubs, occasionally emitting faint squeaks of protest. A long analysis of an obscure 1954 novel in which a convicted murderer frequently refers to one of Housman’s poems, even recalling lines from it as the trapdoor opens beneath her on the gallows, was firmly and rightly excised. Also deleted was an even longer investigation of Enoch Powell’s self-identification with Housman, not only as a brilliant classicist, but also as a lonely figure notorious for his outspokenness and as a poet whose verse – most notably that published in his first volume, inspired, like Housman’s, by his love for another man – was clearly indebted to A Shropshire Lad. The grounds for this passage to be removed were indeed squeamishness – of a political rather than a sexual kind – but it was also true that I had failed to find a convincing place to include it in the narrative.

A book’s hinterland also includes paths that lead somewhere useful and are very tempting to explore further, but are best left until the book is finished. A number of these had to be negotiated while I was writing A Little Book of Latin for Gardeners. Those who are credited with ‘discovering’ plants, although the term is often used in botanical history, were often merely collecting and identifying ones that were already known and named in their country of origin. Similarly, when you are asked what your ‘discoveries’ were when writing a book, you can often only really talk about people or things that were new to you, though perhaps familiar to others. For instance, I knew that William Turner’s The Names of Herbes (1548) and A New Herbal (1551–64) had led to the author becoming known as ‘the father of English botany’, but I did not know that in 1544 he also published (in Latin) one of the first British works of ornithology. Translated in 1903 as Turner on Birds, it includes his own marvellously vivid field observations alongside descriptions – sometimes rather more fanciful – by Pliny and Aristotle. Here was a side track that was very tempting to wander down but had to be sternly bypassed so that I could concentrate on Turner’s writings on plants.

Similarly, I was only able to accompany the French botanist and traveller Joseph Pitton de Tournefort a little way on his journey to the Near East of 1700–1702. This brilliant and fascinating man survived the many hazards of the expedition, which he undertook on behalf of Louis XIV, only to die as the result of being crushed by a cart axle in the street that now bears his name in his native Paris. His Relation d’un voyage du Levant, posthumously published in 1717 and rapidly translated into English, is hugely entertaining. Nonetheless, it was necessary to concentrate on what he wrote about the plants he found on his travels, including the oriental poppy and the azalea, and not get waylaid by his alluring descriptions of the manners and customs of the people he met.

A third discovery was Alice M Coats (1905–78), who published several very lively and informative books on plants in the 1950s, 1960s and 1970s, but seems otherwise to have left very little trace of her life. She started out as an artist, but later began writing about the plants that were a frequent subject of her colour woodcuts and linocuts, drawing in particular on old botanical volumes. Before embarking on such books as Flowers and Their Histories (1956) and The Quest for Plants (1969), she had written The Story of Horace (1937), which, given her knowledge of the classical world, I had imagined to be a biography of the Latin poet. It turned out to be a children’s story about a bear, now very difficult to find and expensive when you do.

So, when people ask you what you will do now your new book is finally at the printer, one answer is that you will go back to read the many volumes you set aside or merely skimmed for relevant information. Returning to that increasingly distant hinterland, you can at last wander with a clear conscience along those paths whose attractions you previously and piously resisted. In the meantime, a new country appears on a far horizon and before you know it the whole process starts again.