Adam Nicolson's grandparents were Harold Nicolson and Vita Sackville-West and the historical detail with which he discusses his forebears and Sissinghurst's foundation is fascinating. Yet the meat of this elegant and perceptive story is Nicolson's account of how he dragged the house into the present day, with the help and occasional hindrance of the National Trust, its owners. Nicolson, by his own account not the worldliest of men, is an unlikely figure to mastermind the restoration of Sissinghurst, but his passion makes this a gripping account. It might now be "a major BBC series", but this tale is quite colourfully enough drawn on the page to have no need of TV pictures.

Thanks to an irresistible combination of lesbian, literary and aristocratic connections, Sissinghurst is the National Trust's most popular destination. But when Nigel Nicolson, whose mother Vita Sackville-West created the garden 70 years ago, died in 2004, his son Adam determined to persuade the Trust to rethink what ad-men would call the Sissinghurst Experience. When his grandparents lived there, the place was supported by a mixed farm, orchards, hop fields, kitchen gardens. Now it was beautiful but dead, like a Titian in a vast carpark. This is the story of his mission to reconnect the garden with the wider landscape: part history, part biography, elegantly written and so sympathetically read by Jeremy Clyde that you're bound to be on Nicolson's side.

Adam Nicolson has different problems from the rest of us. By that I don't mean that he lives in a stately home while everyone else is obliged to fret about negative equity on their semi. Nicolson actually has different problems from the rest of the country house elite. Sissinghurst has always done very nicely indeed as a commercial enterprise. While owners of other crumbling piles have had to resort to stocking chilly-looking rare breeds in the stable block, Nicolson has Vita Sackville-West in all her sleepy-eyed, green-fingered glory to pull in the punters. The garden that Sackville-West (Nicolson's grandmother) created 70 years ago out of a weed-strewn wreck is still a marvel. Add the whole lesbian-literary-aristo thing, mix in a cream tea, and you've got a product for which hordes of people are prepared to pay handsomely.

But for Nicolson this isn't enough. The Sissinghurst "brand" may be performing competently, but since when has competence stirred the soul? A committed environmentalist, he wants to restore the estate - farm as well as park - to its older incarnation as a fully variegated landscape. Instead of presenting visitors with an exquisite heritage garden hedged by dull fields of chemicalised wheat, he wants to give them something richer, more joined-up. By reintroducing the orchards, cattle and sheep that were once a part of Sissinghurst's internal economy, Nicolson hopes to set up an eco-system whereby everything that is consumed in the restaurant or bought from the gift shop is home-grown. Connectedness, authenticity, delight - these are the words he intends Sissinghurst to live by.

Still, it's hard staying connected, let alone delighted, when you've got to do battle with cohorts of vested interests, including the National Trust which now runs the property, and the 35 permanent employees who have already invested decades in making the place work a particular way. In some of the best scenes in this excellent book Nicolson is brought up sharply, though not unkindly, by staff who remind him that he is not the only person in the world who loves this place. Any lingering grand seigneurish tendencies are again cut down to size when he goes to work in the restaurant for a couple of days, the one he is planning to transform into an organic paradise, and finds himself too exhausted by the washing up to care.

In his quest to win over the nay-sayers, Nicolson sets out to demonstrate that Sissinghurst's deep nature has always been about change, not stasis. For a start, it is situated in one of the most porous corners of Britain. Medieval Kentish men and women spoke something that sounded a lot like Dutch and were quick to give proto-Protestantism a sympathetic hearing. Nor did the Weald's scrubby soil support a fully developed feudalism. Instead yeomen scraped away as best they could, supplementing their farm income with profits from the cloth industry, learning habits of energy and self-determination along the way.

It's a beguiling picture of rugged individualism and local difference, but even Nicolson can't really make it stretch to the people who owned Sissinghurst itself. The Saxingherst and de Berham families sound exactly like the sort of people who always pop up in potted histories of grand country houses. So there are good old souls who love the place but won't update, and upstarts with slick new ideas. There are rotten cousins with deep purses and devoted daughters who tend the sickbed and make careful inventories. Still, not every National Trust family can field a baddy quite as bad as John Baker, who was responsible for fashioning a Tudor palace out of a homely medieval manor. A crypto-Catholic in a sea of Protestantism, he specialised in sending people to the stake simply because they found transubstantiation hard to swallow. He ended up a star of Foxe's Book of Martyrs for all the wrong reasons.

Sensibly Nicolson leaves most of his grandparents' story to the last, making it just one episode in a much longer story. Vita Sackville-West famously bought Sissinghurst in 1930 as a solace for not being able to inherit nearby Knole when her father died. Its salmon-pink brickwork became the backdrop for one of the most famous marriages of the 20th century, between lesbian Vita and gay Harold Nicolson. Adam Nicolson is careful not to add another layer of treacle to this much-told story of rich, attractive people doing vaguely saucy things behind the Sissinghurst roses. Instead he gives us a clear-eyed picture of what lifelong love feels like, regardless of how pretty or privileged you are. His description of his elderly grandfather, unstrung by Vita's death, blundering round the dirty, draughty half-ruin that was 1960s Sissinghurst is a bracing corrective to the lingering tendency to romanticise the house's most famous residents.

There are other places in the book, though, where a little more of that discipline wouldn't go amiss. Sissinghurst: An Unfinished Story is written with that heightened lyricism which seems to have become the default mode for the new nature writing. Beautiful in small portions, it can become too rich when poured over page after page, like one cream tea too many. Also unsettling is Nicolson's decision to follow the example of many memoirists and keep his living loved ones out of the story. His wife is all but absent, his children don't have names. You know why people do it this way and, indeed, respect them for their tact. The problem is that it leaves a tracery of gaps and silences in the story which will always alert the suspicious reader. Reading this book, I found myself obsessing about male primogeniture. It was, after all, Vita's unfortunate gender which meant that she had to give up Knole and buy Sissinghurst in the first place. Nicolson mentions several times that he has sisters, one of them older, yet it is he who inherited the family home on the death of their father in 2004. When they get a moment off from listening to Adam bang on about the connectedness, integrity and delight that he's going to restore to their childhood landscape, don't these women, the elder one especially, feel the urge to pinch him very hard indeed?

 Kathryn Hughes's biography of Mrs Beeton is published by HarperPerennial