Arabella Lennox-Boyd is designing the landscape around a 19th century gunpowder store that is being transformed into a £14.5 million second home for the Serpentine Gallery in Hyde Park, London.
The Grade II* listed neoclassical Magazine building from 1805 has been given an extension by architect Zaha Hadid.
The building will be called the Serpentine Sackler Gallery after a gift from the foundation of the late philanthropist Mortimer Sackler and his wife, Theresa.
The opening show from September 28 2013 will feature Argentinian artist Adrian Villar Rojas.
The building was used most recently to store flag poles. Royal Parks invited tenders for its use four years ago, with the Serpentine beating hopefuls including Damien Hirst who wanted to use it to show his art.