Back in March 2011, in what now seems an impossibly ambitious undertaking, I was camera-hunting rare irises on the Golan Heights and looking at gardens in Tel Aviv, Haifa and Jerusalem. It was the first research trip for a book I wanted to write on gardening in the Levant – from Alexandretta (modern-day Iskenderun) in southeast Turkey, to Alexandria in northern Egypt, taking in Lebanon, Jordan and Palestine. The epicentre of my proposed opus would be the Fertile Crescent, involving long stays in Syria over the next few years. Well, we know what happened there… and the project was necessarily abandoned.

I couldn’t, however, turn my back entirely on that part of the world, and regret was slowly overtaken by excitement and intrigue as I recalled a dawn glide down the Bosphorus in the autumn of 2008. Through binoculars from the deck of a small cruise ship returning from Ukraine (lecturing on gardens as part of the ship’s onboard cultural itinerary) I marvelled at numerous old houses and yalıs, shaded by cedars and pines of venerable splendour, suggesting the existence of secluded and perhaps little-known gardens.

Long-term commitments prevented any immediate return to Turkey but in the spring of 2012, as leaves on Istanbul’s plane trees slowly unfurled, I began the prospect of writing about its public parks and gardens, its threatened bostans (community vegetable gardens), hoping primarily to discover a cache of private horticultural havens struggling for supremacy in the concrete jungle or at verdant ease along the Bosphorus shores. While my focus is mainly post-Ottoman I cannot ignore gardens surviving from earlier times or, where hallowed trees still stand, cemeteries and mosques, setting my own boundaries north and south, from the Black Sea to the Princes Islands.

As a stranger, armed with little more than a Turkish dictionary, a map and a clutch of city guidebooks, I began my quest. Unlike the many countries where for more than a decade I have led specialist garden tours, Turkey could not provide a ready-made list of “must-see” gardens. I was starting from scratch in a city where, from a casual glance, any serious gardening seemed to have stopped abruptly a hundred years ago. Yet, so rich was that Ottoman heritage that I refused to believe I couldn’t find enough to satisfy my own Turkish garden cravings – let alone those of today’s many tourists thirsty for foliage and flowers.

With just two days left in Istanbul on that first extended trip, I went to Koç University to meet Scott Redford, who began to unlock doors on my behalf: most importantly that of Nihat Gökyiğit.

If, as an elderly Turkish gentleman sipping tea near Taksim Square told me, “a man can remember a woman with a single flower”, how much more romantic is it to recall her with a whole garden – more than 80 acres of it? Such is the gesture made by the businessman and philanthropist Nihat Gökyiğit in memory of his late wife, Nezahat, and you would be forgiven for thinking it the act of a bejewelled grandee from the Ottoman Empire’s glittering past.

But Nihat Bey is alive and as well as any man in his late eighties can be. On my last full day in the city we met at his office, which he frequents, though far beyond retirement age, as chairman of the board of Tefken Holding, Turkey’s largest firm of construction engineers. We became acquainted over toasted sandwiches and tea before setting off across the Bosphorus to the Nezahat Gökyiğit Botanic Garden (NGBG), a miracle of entrepreneurial horticulture under the directorship of Adil Güner, straddling – improbably – the intersection of two thundering motorways amid a forest of new apartment buildings and the recently completed Mimar Sinan Mosque at Ataşehir, some 20km from the city centre.

Among the NGBG’s glories are the tunnels that connect its various sections, each one an island, each devoted to different styles of gardening and different kinds of plants. One, perhaps 100 metres long, displays reproductions of pieces shown at the Istanbul 2010 European Capital of Culture exhibition. Subtly yet forcefully, each picture demonstrates Turkey’s universal exploitation of floral (especially tulip) and foliar imagery – from both realistic and stylised botanical illustration to landscape and miniature paintings, ceramics, clothes and shoes, soft furnishings, furniture, domestic and marine architecture, jewellery, clocks and tableware. All human needments are embodied, beyond life itself too, in the decoration of tombstones and, chillingly, such instruments of death as daggers, swords and gunstocks. The Ottomans were obsessed by plants and flowers and the skill of its artists and craftsmen was unrivalled. (Doubters might start with Orhan Pamuk’s My Name Is Red.)

For an authoritative account of the Empire’s horticultural brilliance there’s Nurhan Atasoy’s A Garden for the Sultan (Kitapyayınevi, 2011), a book of great beauty and learning. Present-day Turkish designers are free from the confines of what Professor Atasoy describes as being “Ottoman” gardens seen partly in the Islamic mould. “In their westward migrations to seek land that was more fruitful than the arid steppes of Central Asia,” she says, “the Turks brought with them many of their ancient traditions” and, one might add, many plants from countries plundered en route. “Anatolia,” the professor explains, “is a land-bridge linking the flora of southern Europe on the one hand and that of southwest Asia on the other.”

Today’s Istanbul gardeners, in a climate sweetened by lapping water on three sides, can successfully grow a range of plants from two mighty continents, plus almost anything from their own catalogue of native flora, richer by far than any found in neighbouring states. Moreover, foreign travel, books and magazines are influencing a younger generation of garden designers, especially those hired by private clients (who may not be Turkish) or who seek merely to green-up an urban roof terrace.

Regrettably, an overcrowded Istanbul cannot provide new houses with large individual gardens, although in a meeting with Ihsan Şimşek, head of the city’s parks department, I was assured that current and proposed developments are being given recreational green spaces.

I have now made detailed notes about some of Istanbul’s better-known palace gardens (supremely Topkapı) and the city-owned Yıldız and Emirgan parks, where a vibrant style of municipal bedding-out appears to please the visiting hordes. Emirgan Park is lately revived by the conversion of old brick stables and carriage houses to accommodate the new Istanbul Lale Vakfı (Tulip Foundation): in its grounds the famous Tulip River is replanted each autumn with thousands of bulbs in advance of the citywide annual Tulip Festival.

I spent time at Istanbul University’s now sadly doomed 1930s Alfred Heilbronn Botanic Garden by the Süleymaniye Mosque, on a prized (and therefore super-valued) site overlooking the Golden Horn. Up in the Belgrade Forest, near Bahçeköy, a 45-minute Number 42 bus ride from Taksim Square, I combed the paths that delineate the species-rich Atatürk Arboretum in the company of the botanist Rahim Anşim. Within the book-lined walls of Nurhan Atasoy’s city-centre apartment I learned how today’s gardening is linked to the past, and from designer Gürsan Ergil, one of whose latest commissions is a garden for the new Turkish Embassy in Mongolia, I took the pulse of contemporary horticultural trends.

If those were some of my sunnier moments, then my darkest hour was spent on the Saturday afternoon of June 15 in Gezi Park. Threats to these few acres and their indispensable shade trees triggered the “riots” that much hampered my second summer visit this year. Yet, with the memory of teargas in my eyes I am eager to return, to trawl the city again, to peep behind locked gates and over high walls, to talk to gardeners young and old – all in search of Istanbul’s elusive parks and gardens.