The golden weeks of garden-visiting in Britain are just beginning. The season may be early, the roses may be fading but the next weekends are the time to catch gardens great and small at their peak. In anticipation, people have been asking me the most curious question: have I seen Sissinghurst?

It is a curious question because I first visited Britain’s most famous garden in 1965, when one of its founders, Harold Nicolson, was still well enough to be watching intruders from a chaise longue beside the main house. I then stayed there in magical conditions in the 1970s and 1980s and enjoyed the unmatched pleasure of the best of the roses and the White Garden with nobody else present.

I remember the family resident at the time, Nigel Nicolson, startling his few guests by imitating the hoot of a barn owl as we admired the garden’s white flowers by dusk. It was an eerie moment because the garden’s planter, his mother Vita Sackville-West, had written long ago that she hoped one day to see a white barn owl floating over the all-white garden, which she was about to plant under the flakes of winter snow. Nigel then invited me to select a choice of her inimitable gardening articles, a job for which he let me see a great treasure, her first garden diaries when she was setting out on her career. She was as ignorant as all beginners are about the likely height of lobelia.

Have I seen Sissinghurst? It is like asking the FT’s film critic Nigel Andrews if he has ever seen Gone With The Wind. Actually, it is more like that than I realised. The Sissinghurst in question was not the garden but the eight-part television series about the place, which has been fascinating viewers on BBC4 this spring. I hate gardening in remorseless sunshine between 11am and 4.30pm. During the recent bout of it I sat indoors, glued to the TV re-run instead.

It is unmissable. Sissinghurst was given its great garden by Harold and Vita between 1930 and 1961 and since then it has been perpetuated by the National Trust. Descendants of the “donor family” have the right to live on in part of the property, a standard deal for those who endow their historic homes to the Trust. After Nigel Nicolson’s recent death, the main residents are his thoughtful son, the writer Adam Nicolson, and Adam’s wife, Sarah Raven, celebrated in her own right as an apostle of cut flowers, good cooking and garden courses in their nearby property Perch Hill Farm. Amazingly, they had invited the BBC to follow the progress of their plans to energise Sissinghurst’s surrounds. I expected a spectacular act of horticultural suicide.

Adam is so analytic and frank that viewers cannot help relating to him. Sissinghurst’s fame also rests on his parents’ independent sex life, especially his grandmother’s female love in the garden for the novelist Virginia Woolf, and BBC4 is even more blunt. In the very first shots of the series, we learn that Vita had “50 female lovers”, about 45 more than I realised. Many of them reclined on the very sofa still visible in her shrine of a room in Sissinghurst’s tower. “We are the lesbian headquarters of England,” Adam muses as the visitors begin a new season. “At Easter, there will be rivers of lesbians coming through that gate.”

The scene is set for a classic, unscripted glimpse behind the scenes. It turns on his and his wife’s hopes for change in the restaurant, the surrounding landscape and the methods used by Sissinghurst’s farm. “We enjoy lovely privilege,” Adam explains winningly, as a “resident donor” family “but we are not in control”.

I gleefully awaited Sarah, who trained as a doctor before marriage. The satisfied takers of her courses in gardening know exactly who is in charge. So does Adam, who happily admits to taking his instructions from his wife. Her speciality, he tells us, is making lists.

The Nicolson plan is to return the Sissinghurst farm to the mixed farming – animals, fruit and produce – that characterised it in the 1950s. Nowadays, it is a “diminished landscape”, run by absentee tenants who farm it chemically for wheat. The excellent idea is to restore vegetable-growing, one of Sarah’s crusades, and use the produce to freshen the recipes in that British bastion, the National Trust restaurant.

When she appears, striding purposefully in gumboots over her planned vegetable field, you may think you are going to see yet another BBC send-up of bossy toffs foiled by ordinary people, supposedly the salt of the earth. “I feel I am bashing my head against a wall,” she not unjustly reiterates after the 11th meeting of the Trust’s Food Committee. Adam, meanwhile, has endured the 63rd meeting of the Farm Project Committee. It is a classic tale of micro-management, what Adam starts by calling “sterilised corporate crap”.

Programme director Clare Whalley has been far too wise to impose a stereotype. She has let a dream team of participants simply be themselves. Every member of the public before the camera is a natural star. Sarah is a superstar to whom my heart rapidly goes out.

Like all superstars, she needs her match. She finds it in Steve, the commercially trained chef who has been feeding standard British dishes to the Sissinghurst paying public without any wish to introduce Sarah’s trendy cous-cous. He tells us he “does not do meetings” and, better still, that the hairs on the back of his head go up whenever he hears the word “consultant”. When Sarah confronts him with rocket and a side dressing his face says it all. The Trust stands for British dishes and they mean turkey and beef, with roast potatoes and pre-dresssed salad.

Sarah is an emotional being beneath that sense of purpose and deserves an award for unscripted performance of the year. Adam even comes round to corporate crap as a way of creeping forward. There are no villains and, when the new vegetable director, blonde Amy, takes over a grim field of Kentish clay, she turns it in five months into a vegetable paradise that feeds the restaurant daily. I want to nominate her for one of the Queen’s Birthday Honours.

In the end, one Moroccan lamb tagine makes it with Sarah’s help on to the Trust menu and only for a week. Adam’s organic plans have yet to find a tenant to carry them out and nobody is going to reduce the visitors’ picnic-lawn by turning it over to free-range pigs. The one winner is good old gardening, dynamised by the new acres of vegetables. There is no faking there, no phoney make-over for Gardeners’ World.

I have only one complaint. Sissinghurst’s greatest years in public ownership owe an immense debt to the two supreme lady gardeners who were appointed by Vita herself. In the 1970s to 1990s, Pamela Schwerdt and Sibylle Kreutzberger made it a truly great garden for all seasons. They met as girls in the dormitory on the garden course at Britain’s old Waterperry School and have been a couple ever since. They do not deserve a TV award. They deserve to be Companions of Honour for all they have done to keep Sissinghurst at its peak. In the series, sadly, they are never even mentioned.