His passion for gardening and his impressive depth of knowledge were conveyed in a relaxed and affable manner that inspired confidence in experts and novices alike. When he had his first heart attack last year, thousands of viewers sent him flowers and get-well greetings. Over the years, many presenters tried to copy his style but never achieved the right balance. It is hard to be matey without seeming to patronise; to celebrate floral beauty without being precious; to play the countryman without tipping into the character of the country bumpkin, as some of his predecessors and contemporaries had done.
In fact, he was not a countryman at all, being perversely proud of his origins in Stepney, east London, where he was born one of twins. When he was two, the family moved to rural Hertfordshire, where he soon developed an interest in gardening, taking part-time work in a local nursery while still at school.
After graduating from agricultural college he became a nurseryman and landscape gardener, and began writing a column for Garden News in 1970. Five years later he took up journalism full-time and became editor of Practical Gardening.
His colleagues in the media liked him because it was impossible not to: he was invariably friendly, helpful and, on screen, utterly professional. In 1991, when the BBC put Gardeners' World out to an independent producer, there was never a doubt that Hamilton would stay as its main presenter. Tony Laryea, whose company, Catalyst, was awarded the contract to produce the show and who is now its executive producer, said: "Geoff had a genuine love of gardening: it came out of every pore, and he was able to communicate it effectively because he was an ordinary bloke. He wasn't pretentious. He had a no- nonsense approach and an authority that came through his knowledge. You saw it and you believed it.
"New people on the programme were amazed when they saw him in front of the camera. It all came so naturally to him. If something hadn't worked he could tell straight away and he would do it again, getting it exactly right. He also had a marvellous sense of humour."
Last Friday, two days before he died, Hamilton was busy filming segments for this week's edition of Gardeners' World. He had simultaneously been working on a new series called Hidden Gardens, due to be screened next January. It was to be a follow-up to last winter's highly successful Cottage Gardens: his book accompanying that series was on the best-seller list for months.
On this week's Gardeners' World he had been due to guide viewers on a tour of his large garden at Barnsdale in Rutland, partly financed by the BBC. It was also his home, where he lived with his second wife Lynda. Although the public are seldom allowed into Barnsdale it is one of the most famous gardens in the country because Hamilton's demonstrations of gardening techniques were filmed there. It is made up of several distinct garden areas, many constructed in front of the cameras for the benefit of viewers.
He seemed less comfortable when presenting the programme from other people's gardens and being forced to enthuse over aspects that he may not necessarily have liked. He was happiest on his own patch explaining practicalities, wielding the spade or hoe or getting his hands and knees dirty. With such a wide audience it was inevitable that his ideas should influence horticultural fashion: for instance, his habit of mixing vegetables and flowers in the same border is increasingly imitated.
Gardening is a big-money leisure industry but Hamilton was not a reliable friend of business interests. Knowing that many of his viewers were pensioners, with little money to spare, he directed much of his advice towards saving costs. Why use purpose-made flower pots when you can recycle yoghurt containers? Or buy an expensive cloche when you can make one yourself for a few pounds? His penchant for low-cost improvisation, allied to his perpetual air of boyish innocence, sometimes made the programme feel like a grown-up version of Blue Peter.
His millions of fans did not include the makers of fertilisers and pesticides. He was an organic gardener, eschewing chemicals and passionately opposing the use of peat in potting composts because extracting it from the earth can endanger natural habitats. Although never cranky or obsessive about ecology he was one of the first New Age gardeners, politically correct before the phrase became fashionable. As such he was in sharp contrast to Percy Thrower, the first presenter of Gardeners' World, summarily fired from the programme in 1975 for the sin of making television commercials for garden chemicals.
A widely known gardening expert has numerous calls on his time: not just the on-screen work, but newspaper and magazine articles, books and endless personal appearances. Some of Hamilton's friends think it was his reluctance to turn down such engagements, as well as having to find the time to do his own gardening, that contributed to last year's heart attack.
He was off the air for three months while he recuperated, and on his doctor's orders lost weight and took more exercise, including cycling. The fatal attack occurred while he was on a charity bike ride at the weekend, doing his bit for a good cause while trying to keep fit.
Geoff Hamilton, journalist, broadcaster and gardener: born London 12 August 1936; twice married (three sons); died near Merthyr Tydfil, Glamorgan 4 August 1996.