The founder of the Eden Project in Cornwall says the troubled National Botanic Garden of Wales is a "national treasure" which should be championed.
Middleton a "national treasure" says gardens expert
Tim Smit visited the attraction on Saturday to offer suggestions and show solidarity to save the £43m project from extinction.
Mr Smit said the progress of the garden had been "phenomenal" and claimed it had a "fantastic future."
"It's a national treasure and it will be hugely successful," said Mr Smit,
adding that the Welsh assembly should act as a "proper champion" to the garden to secure its future as a national institution.
Mr Smit said no-one was asking for an open cheque book but added: "The assembly should show it has taken the garden to heart by supporting it as much as it feels able."
Praise for Middleton
It certainly should be supported. It's a terrific asset
He said the assembly should work with bodies including Defra and the
Millennium Commission to support the west Wales attraction.
Mr Smit added: "It should certainly be supported. It's a terrific asset."
According to the Welsh assembly, Middleton built up a debt of £2million as visitor numbers dropped from 220,000 in 2000/1 to 150,000 for the 2002/03 financial year
But Mr Smit said that a national institution which aimed to be in place for several hundred years was very different from a theme park.
He said: "It would be crazy to assume it would break even in three years."
Unfair to compare with Eden site
He added: "The staff have done a great job in very trying circumstances."
Earlier this week, there were fears the garden would close next week after trustees said conditions placed on a rescue funding package were unacceptable.
But trustees chairman Alan Hayward later said he was hopeful the trustees could accept £150,000 offered by Carmarthenshire Council after meeting chief executive Mark James.
Mr Hayward previously said the trustees of the site at Llanarthne, west Wales, wanted to accept the money and continue talks with un-named potential partners.
Mr Smit stressed it would be unfair to compare the success of the more commercially-based Eden Project with the Welsh garden.
He said whereas the Welsh garden had been set up as a botanic institution, Eden was "rock and roll" with "no rules at all."
Eden project founder Tim Smit - appeal to Welsh assembly
A team of about 40 volunteers has started work to try to maintain the Middleton's stock of 100,000 rare plants.
The volunteers, dubbed the Yellow Brigade because of their yellow uniform, include retired professionals, students and a Mencap member.
Seventy-five per cent of the staff workforce will be made redundant on Wednesday.