On the 92nd level of Melbourne's Eureka Tower, two little plants have survived for months without soil or direct water. Caged and strapped to a rusty pipe, they endure winds of up to 200km/h at their lonely outpost high above the city.

The pioneering installation – thought to be the tallest rooftop garden in the world – is part of an experiment to see if it could be possible to grow plants on top of every building in the city centre.

While "green walls" and "urban forests" are often spruiked in glossy brochures for new skyscrapers, they are not always a success. Like the top of a cliff, the tips of high-rise towers can be inhospitable.

For the past eight months, ecological artist Lloyd Godman and his team have been breaking new ground on top of Melbourne's tallest building. They have installed eight Tillandsia flowering plants on levels 56, 65, 91 and 92, the very top of the 297-metre building.