Gardens: Private viewing

My copy of the essential London map, the A-Z, was ripped from my hands by a television director I was working with who couldn't stand the fact that my old black and white version didn't even show the Hammersmith flyover. My excuse – "But nobody lives on the Hammersmith flyover" – didn't wash and he bought me a new A-Z in colour. For the first time I could see how much green was spattered about the pages. Even on my old map you could pick up the big public spaces: Hyde Park, Kensington Gardens, Victoria Park out east, Ravenscourt Park out west. But the new map showed the tiny sliver of green running through the middle of Chester Square, SW1, and the slightly larger stripe separating the two sides of Montagu Square, W1, the elegant circle of Fitzroy Square in W1, and the extraordinary amount of leafiness scattered around South Kensington.

This weekend is your opportunity to get into these places. The London Parks and Gardens Trust (LPGT) has persuaded the communal owners of more than a hundred of London's most private spaces to open the locked gates and share their lives. Bina Gardens East, SW5 is almost too small to show up on the A-Z at all, but it's an enchanting wedge-shaped bit of land, a third of an acre left over after the red brick terraces of Rosary Gardens and Bina Gardens were laid out by a Mr Measures some time in the 1880s.

Between the two, at an angle, runs the quiet backwater of Dove Mews and at the end of the mews, there's the garden, screened behind a light-limbed and rather handsome green-painted railing. Either side the space is contained by five-storied terraced houses, most of them now converted into flats. Standing there admiring a huge and unusually handsome Ligustrum lucidum at the back of the garden, the sun glittering on its evergreen leaves, the loudest noise I could hear was a blackbird singing.

Much of the gardening that goes on in this space is done by Susie Maier and her friend, Alice Ulm, who owns one of the houses that backs on to the garden. Usually, these communal spaces seem to be run by a trust or a residents committee. This garden was sold off by the Gunther Estate when they got rid of all their surrounding properties; a couple of years ago, it came up for auction again, and Alice Ulm bought it. Though everyone living there can use the garden, contributions to its cost are voluntary and very few give anything at all.

But the way it is owned allows a wonderful freedom in the way it is gardened. Roses and clematis tumble over the railings. The grass is lush, the paths interrupted by falls of geranium and ceanothus. There's a prize specimen of the wedding cake tree, Cornus controversa 'Variegata', a slow-growing and rather expensive thing that perhaps you would not want to risk in a space where footballs are regularly flying through the air. Melianthus, untouched here by frost and cardoon, shine palely from dark corners. Ms Maier spent a long time cleaning out what had once been a small pond at the back of the garden – "five sets of salt and pepper pots. Why?" – and the still boggy area supports a handsome colony of royal ferns, angelica, rheum and other things that are glad of the damp under their feet. It's a surprising, happy little oasis and it's open today (10am-5pm) and tomorrow (10am-5pm).

You could plot an entire day trawling through this area of London: of the 113 private gardens on the LPGT list, 40 are in the "SW" postcodes, another 35 in the "W" ones. The squares of the Kensington and Chelsea Borough tend to be just that: Belgrave Square SW1 (open Sunday 10am-5pm), Thurloe Square SW7 (open Sunday 10am-5pm), Kensington Square W8 (open Sunday 1-5pm) have their green space in the middle of a square of houses. They are private, in the sense that you have to be a keyholder to get inside them, but rubberneckers like me can peer into the gardens from the pavement, though there's usually a good shrubbery of sooty-spotted laurel protecting the space inside.

If you move north, into Notting Hill and Maida Vale, the pattern changes. There's an astonishingly large communal garden, three acres of it, tucked behind the terraced villas of Elgin Crescent which is shared with neighbouring Blenheim Crescent, but if you wander along either of those roads, the bland stuccoed façades of the 1840s houses give no clue to the outsider of what lies behind. Each of the properties has its own back garden, but each of those private gardens give on to this huge sausage-shaped communal space, with some good trees and plenty of grass for kicking about on. Because each house has its own decent back garden, there's little pressure to garden the space beyond and plenty of dogs and children who are glad of the untrammelled acres. But there are a few glitzy gardens ranged round the outer ring of the communal space. Spot the Jinny Blom designs – three (I think) almost in a row on the Elgin Crescent side. The Blenheim and Elgin Crescent Garden (access between 81-83 Blenheim Crescent) is open Sunday (2-5pm).

Moving even further north into Maida Vale, there's a similar space, Crescent Gardens, shared between the villas of Randolph Crescent and Warrington Crescent. On my new map this isn't coloured green at all, but here's another wonderful three-acre garden, with fine great high-crowned plane trees marching round the edges and dark old rope-edge tiles bordering the wide perimeter walk. Most of the houses here have been converted into flats and even the ground

floor ones have only tiny back patches to call their own. Consequently there's more pressure here to garden the communal space and the Crescent Gardens are run by a powerful Gardens Committee who employ a professional, Robert Player, to look after the grounds. Last year, Crescent Gardens won first prize for large gardens in the annual competition organised by the LPGT and I'm not surprised. It's beautifully planted, yet still manages to accommodate a yearly bonfire party and two big Christmas trees lit up by an electricity generator carefully concealed among the flowers.

But communal enterprises often depend on the energy of one or two individuals, and at Crescent Gardens all fingers seemed to point at Virginia de Vaal, who's lived in Randolph Crescent for the past 18 years. She walked round with me and there was scarcely a moment when she wasn't scooping up something she didn't want to see – silver foil, paper handkerchiefs, broken flower heads, stones on the grass – in a way that suggested a deep personal commitment to the place and its future.

They've got money to spend here: 93 houses, most of them divided into five flats, each tenant paying £100 towards the maintenance of the gardens. But money alone doesn't make a garden and this is a good one – well-chosen shrubs, lush herbaceous planting, carefully aerated lawn, herbs, seats, an arbour plastered with wisteria. What's the biggest problem here? "Finding spaces for the kids to play without damaging the plants," said Ms de Vaal. After our walk, she showed me the records of the garden committee when at one of their first meetings, 24 March 1893, parents were "urgently requested to use their influence" to stop children playing on a newly seeded area of grass. Some things never change. Crescent Gardens (entry by 1, Warrington Crescent) are open Sunday (10am-5pm).

For a full list of the gardens taking part in the London Squares weekend and opening times, visit opensquares.org. Tickets (£7.50) allow entry to all the gardens opening this weekend and you'll get a guide book as well. Buy tickets at the first garden you go to. Children under 12 go free