A great pleasure of London’s Open Garden Squares Weekend, which takes place this coming weekend and includes 176 gardens, is the opportunity to nose around properties, many of which are usually only glimpsed through railings and locked gates. These range from the grand garden squares of Kensington and Chelsea to community plots, schools and hospice gardens.

Some, however, are even more private. One such property is Conisbee Courtyard in Islington, north London, an innovative combination of six residential flats and office space (which belongs to a structural engineering firm) set around three floors of exuberant planting. Although the courtyard and balconies are accessible only to Conisbee employees and guests, the flats’ occupants get the benefit of a view of lush greenery without the chore of having to look after it themselves. That is the job of Marie Clarke, a landscape designer who works with Conisbee on projects and who oversaw the space.

At ground level is a cool courtyard filled with leafy plants that include 100-year-old tree ferns in large galvanised-steel containers. There is also a rectangular pool, carefully positioned to allow room for party gatherings around it, and planted with flag irises and marsh marigolds, through which goldfish swim.

At the sunny end of the courtyard, Clarke is experimenting with a “green wall”, in which a wire frame is hung on the wall like a painting and stuffed with plants such as euphorbias, heucheras, geraniums and ivy. “It’s for environments where there is no space otherwise, where you can’t easily garden in the more conventional way,” she says.

On the next floor are decked office balconies, all planted with an abundance of green, while at the top, where the sun hits the building, large planters are filled with silvery Mediterranean plants. These include olive trees, echiums, geraniums and herbs, which appreciate the dry conditions. Here, to one side, is a flat roof covered in rubble, sedum and wildflowers.

This “green” roof is another example of cutting-edge horticulture. The 4in-6in of rubble covering the asphalt comes from the building works below and gives the area a slightly lunar appearance. The roof, which is not strong enough to support anyone sitting on it, is not just a pretty sight for the Conisbee workers and neighbouring houses to look at, however. The plants absorb rainwater, so the runoff after a heavy downpour is reduced, putting less pressure on the sewers.

Conisbee Courtyard is one of 20 gardens opening this year for the first time. Others include Dan Pearson’s scheme at the Maggie’s Centre in Fulham, and Meanwhile Gardens, four acres of former wasteland in North Kensington, which is now a wildlife-friendly community space.

Popular favourites include Kensington Roof Gardens, an acre and a half of lush planting above Kensington High Street, and the floating greenery at Garden Barge Square, near Tower Bridge. With advance booking, you can even visit HMP Wandsworth and Holloway – two gardens normally kept firmly under lock and key.

Conisbee Courtyard, N1, is open on Saturday and Sunday, June 7 and 8, from 11am to 4pm. For details of London’s Open Garden Squares Weekend, visit www.opensquares.org

Open spaces

The Japanese gravel roof garden at the School of Oriental and African Studies (Soas), WC1

The grounds of Carshalton House, SM5, which include an 18th-century grotto and a baroque water tower, with orangery, pump room and plunge bath

Allen Hall, SW3, with its 15-acre site, was home to Sir Thomas More in the early 16th century and is now a Roman Catholic seminary

Explore Gardens

• Hampton Court Palace Flower Show

• Chelsea Flower Show

Times recommends

• Second homes: credit crunch casualty or money-spinner?
• How I built my own sliding house
• Top 10 incentives for house buyers