London Garden Squares Day: It's hip to be square

No, not Trafalgar or Leicester, but the hidden gardens that offer sanctuary from the bustle of the big city. And on Sunday they're opening their gates to everyone, writes Christopher Hirst

From the balcony of Averil Zamiboni's first-floor flat, the view is a scaled-down version of Central Park. You see the upper branches of plane trees, swirls of clematis, gaudy explosions of climbing roses and, here and there, the opposite side of Eccleston Square, London SW1. "When you get into the garden, you wouldn't know where you are," said Averil. "You smell the flowers and hear the blackbirds and London disappears." Next weekend, this idyllic backwater, usually reserved for Chelsea's smarter set, will be opening its gates to the masses as part of London Garden Squares Day.

This Sunday, when 70 flowery bowers across the capital swing open the wrought-iron gates, we mere mortals can re-enact the scene in Notting Hill when Hugh Grant woos Julia Roberts in a private garden square, or simply admire London's expensively maintained hidden greenery. Also included are such cherished enclaves as Charterhouse Square, with a design dating from the 17th century, and the three acres of Edwardes Square in Kensington.

Averil Zamiboni turned the lock and we entered a landscaped grassy expanse so large that the picnickers at one end seemed unaware of a spot of topless sunbathing at the other. The 275 keyholders include square residents and 100 outside subscribers. Each pays £110 a year for upkeep. It's a hefty price, but this is a priceless asset.

Eccleston Square came about when Thomas Cubitt, who developed it in 1845, had the idea of gathering everybody's back gardens together. Around the periphery, a shady walk took us though arches of wisteria and clematis. "This is a handkerchief tree from China," said Averil. "These irises came from Monet's garden in Giverny." Perhaps the most outstanding of the fragrant eruptions of climbing roses was an apricot affair called Alchemist, which illuminates a vast holly tree. And somewhere amid this horticultural treasure trove is the national collection of ceanothus.

If this all suggests that the Square benefits from the help of a garden expert, you'd be right. Roger Phillips, writer of best-sellers on floral and mycological themes, is a resident. "Twenty years ago we persuaded him to become gardening manager," Averil said. "What you see is his vision, but residents take responsibility for other areas."

We passed a bottle-brush plant that resembled a clump of maroon sparklers. "We have a fine bed of Australian plants thanks to a resident who spent many years there," Averil said. Near the mesh of the tennis courts, threaded with blue geraniums, foxgloves and alliums, she took a deep sniff from a bank of climbing roses. "Oh, that smells just like an English country garden."

Close to the bustling thoroughfare of Walworth Road in Camberwell, south London, is Addington Square, a perfectly preserved rectangle of late 18th- and early 19th-century domestic architecture. This is one of half a dozen public squares joining the private enclaves for Garden Squares Day. "We'll have the usual things – bouncy castles, face-painting, a steel band and plant sales from Walworth Garden Farm, who do projects with disabled people," said the local resident Jill Anderson.

Addington Square was relatively prosperous in the 19th century. It took a pasting during the war when bombers aimed for the nearby canal, and was nearly demolished soon after due to bad sanitation. Now, this fascinating corner is on the brink of respectability. Jill hopes Southwark council will replant the square's floral plots in time for next Sunday.

One exceptional community taking part in London Garden Squares Day is Westminster Abbey, which contributes three squares. A tiny, verdant patch called St Catherine's Garden is taking part for the first time, but the most breathtaking is the College Garden. Behind this domain is a horticultural fiend in clerical robes. Canon David Hutt lives in an 18th-century terrace on one side of this extraordinary London square. The other is formed by a wing of Westminster School dating from 1730. Looming to the north is the 19th-century skyscraper of Victoria Tower; to the south are the pinnacles of Westminster Abbey.

This is possibly England's oldest garden. "The ground has been in constant cultivation for 900 years, beginning as the Abbey's herbarium," Canon Hutt says. Though medicinal herbs are no longer grown (the soil is too polluted), he insists: "We're providing the kind of environment any holistic counsellor would approve of." The garden boasts two of London's tallest plane trees and a wonderful wild garden. A large vine spreads its tentacles in a corner, while a magnificent fig tree rests on a metal support like a crutch. At dusk you can spot some of the garden's pipistrelle bats.

Though ancient, the garden constantly moves on. A black mulberry has been planted to mirror a white one. A new fountain in black marble spouts to celebrate the Queen's jubilee. College Garden is one of London's most magical spots. You can see it from Tuesday to Thursday during the summer and, of course, next Sunday.

For details of London Garden Squares Day call 0870 333 1181 or visit myweb.tiscali.co.uk/london.gardens. Tickets for entry to all 70 venues cost £5 (under 12s free) and are on sale at participating squares