It's not difficult to see what the high point of this year's Chelsea flower show will be. Diarmuid Gavin's pyramid-shaped garden will stand more than 80ft tall - with a Fiat 500 car balanced on the top.
The seven-storey garden-in-the-sky, which resembles a diminutive sibling of London's Shard building, is constructed from scaffolding, with each floor providing a showcase for a different form of horticulture. There will be more than 3,000 plants from huge trees and bamboos to small pots of flowering daisies.
"I've always loved the notion of the Hanging Gardens of Babylon, why it was built and how it was built," Gavin said. "I love gardening in unexpected places and I think it follows from the idea of gardening in roof situations, opening up views to the city."
The Chelsea flower show, which opens in the grounds of the Royal Hospital on May 22, is more usually noted for conventional gardens and sedate visitors. Not so Gavin's garden. "I'm putting the old Fiat I found in a bog in Leitrim, on the top, with nettles and a birch tree sticking out."
It is not the only unusual element: an American-style Silver Bullet caravan will be on floor three, while on the fourth floor there will be a Victorian greenhouse.
Floor five will have a shower and a bath, complete with solar-powered hot water because, according to Gavin, gardeners in the future might be washing in the fresh air. Their modesty will, however, be preserved by exotic foliage provided by a cabbage tree and a Chinese windmill palm.
The sixth floor will have dwarf pines and a billowing carpet of thyme and sage.
In the centre is a lift manned by a bellboy kitted out in the uniform of a 1920s New York hotel. A tubular slide descends on the outside from the fifth floor. Whether people will be allowed to go up to the higher floors during the flower show has yet to be decided.
"It has plenty of different inspirations," said Gavin. "When I was at Chelsea last year I looked at Albert Bridge, which was covered in what appeared to me terraces of scaffolding. That gave me the idea."