We're not short of green spaces in London town – we have more than any other European capital. But some gardens are kept under lock and key – most of the time. Seize your chance this June to step into the secret gardens of London, part of Open Garden Squares Weekend.

More than 200 gardens will be unlocked for one weekend to take part in this annual event, organised by the London Parks and Gardens Trust.

Spanning 27 boroughs, the gardens take in all sorts of spaces, from traditional squares to roof terraces and allotments, as well as gardens belonging to historic buildings, schools, shops and cafes. If you have ever fancied poking your nose into the lost gardens of St James's or seeing the breadth of London's green rooftops, book on to one of the specialist walking tours on offer. We really like the sound of the behind-the-scenes exclusive tour of Kew Gardens, where you visit the tropical nursery, home of their reserve scientific collections.

If, however, you're priority is seeing as many cultivated green spaces as possible, hop on a bike and join one of three different group rides. Participating locations will also host workshops including soap-making, bee-keeping and seed-planting.

Check out the River Cafe garden on the banks of the Thames at Hammersmith, where herbs, salads and edible flowers inspire and infuse the restaurant's world-class menu. Or head up to the edge of Regent's Park to The Royal College of Physicians’ medicinal garden, both beautiful and educational, with some 1,000 species of plant. Each of the plants has a healing or health-promoting property – including local anaesthetics, treatments for swine flu, leukaemia, diabetes and cancers.

This year, the rose-lined garden at 10 Downing Street will also be open to a limited number of visitors chosen following a ballot – you can now apply for tickets here.

The complete programme of events is now live. All events and activities are free with the purchase of a weekend ticket. Tickets are allocated on a first-come-first-served basis, and can be purchased here.