How do you mow your lawn?

It could be the toughest lawn-mowing job ever. The 100-foot walls of the National Theatre have been covered in grass. And the giant lawn on two sides of the South Bank building has had commuters doing a double take as they cross Waterloo Bridge.

The £50,000 project is the brainchild of artists Heather Ackroyd and Dan Harvey, who coated the concrete walls in clay and then planted millions of seeds. Maintenance workers water the 750 square metre grass carpet with giant sprinklers from the top of the building.

Ackroyd and Harvey, both 47, have been making grass art installations since the early Nineties and say it is a reminder of fields in the midst of the city.

The grass will stay on the side of the Lyttelton flytower for six weeks.