Inspired by actress Joanna Lumley, plans have been drawn-up by Thomas Heatherwick who designed the London 2012 Olympic cauldron.
Garden designer Dan Pearson is masterminding the planting. The bridge would span the Thames in London.
Joanna Lumley said: “This garden will be sensational: a place with no noise or traffic where the only sounds will be birdsong and bees, while below will be the steady rush of water.
“There will be grasses, wildflowers and plants that are unique to London’s natural riverside habitat.
“I believe it will bring to Londoners and visitors peace, beauty and magic.”
A public consultation runs until 20 December. Fund-raising is underway.
The bridge would be completed in 2017.