Nigel Dunnett urged designers not to be weighed down with a sense of "doom and gloom" about environmental problems in cities. Now was a big opportunity to use more innovative thinking and daring planting schemes, he added.
"This is already happening in small-scale applications," said Dunnett, a reader in urban horticulture at the University of Sheffield. "But how can we replicate fantastic quality in public landscapes?
"A lot of designers are more interested in hard materials and paving. We need a revolution in the way we think of landscapes. The role of plants is often sidelined. It's a battle, but it's worth pushing for diverse planting,"
He said clients and designers often specified under the mistaken belief that native species were always best for wildlife. Many of his landscapes such as open spaces for the Olympic Village were packed with native and non-native flowers, which were often better resources for wildlife than native plants.
Designer and television presenter James Alexander-Sinclair said: "The lyrics of garden design are in the plants. It's not about hard landscaping. Nobody ever wrote a poem to a patio."
The designers were speaking at a conference in Birmingham hosted by the Society of Garden Designers and the Association of Professional Landscapers last week.