"I wouldn't get involved with this project if it was not of significant benefit to the community and the horticulture world as a whole," Gardiner explained.
Last month, a launch at Harrods raised £257,000 for the £175m bridge, which is seeking public funding as well as private donations. Gardiner said test boreholes have been drilled and work will start next year, with opening scheduled in 2018.
"The bridge is great for communities on either side and great for the horticulture industry. There's no other project like this anywhere in the world."
He had praise for Pearson's design. "Like any plant community it goes from bulbs to annuals to herbaceous to shrubs to trees," he said.
"People are going to love this. There may be a few who are negative about it but a significant percentage of the community will be positively affected."