The National Trust aims to boost its urban street credibility by co-running the London-focused Open Garden Squares Weekend, which throws open the gate to communal gardens.
London Parks & Gardens Trust (LPGT), which last week announced 9-10 June as the dates for this year's event, said the tie-up with the trust was a first for the 13-year-old scheme. The National Trust is helping with funding and promotion.
National Trust director of London Ivo Dawnay said: "The value in being involved is that it raises our presence in London and draws attention to the things we value - gardens, the outdoors and the green environment.
"We don't have a big presence in the capital or other big, crowded environments. In fact, we are a very small player in London even though we have wonderful things further out such as Morden Hall Park and Osterley Park."
The trust has around 250,000 members in London, which amounts to around five per cent of the population. Membership in non-urban areas is nearly double that and the trust is "less visible", said Dawnay. There are, however, no targets on upping membership.
"Open Garden Squares Weekend attracts about 10,000 people. We think that it is one of the best things in the London year and absolutely love it. It's at the early planning stages and we may set bells and whistles ringing later with press and web pushes."
Around 200 communal gardens from historic gardens to roof terraces and allotments are taking part, many not open to the public. They include Wormwood Scrubs, Eaton and Arlington Squares and - new this year - the Queen Elizabeth Hall Roof Garden.
Open Garden Square Weekend Taking Part
Private, institutional, commercial and communal gardens in London take part in Open Garden Squares Weekend.
They include gardens to squares, religious buildings or city livery companies, shops, offices and restaurants and public buildings such as schools and museums.
Cable St Community Gardens opens this year along with Regent's Park Allotment Garden, Kensington Roof Gardens and George V Memorial Gardens, which celebrates its 75th anniversary. One £9 ticket allows entry to all venues.