Perth and Kinross Council has been accused of hypocrisy over efforts to save the Cherrybank Garden Centre.
The Calyx project would have created a 61-acre garden in Perth
Scotland's Garden Trust said the site would have to close, in part, because of a lack of support from the council.
The closure follows the collapse of the £40m Calyx project which would have seen the site transformed into a 61-acre national garden for Scotland.
Ian Miller, the leader of the local authority, described the accusation as "ludicrous".
SGT said that despite claiming to support the project, the council had never come forward with funding.
The Cherrybank Centre in Perth was gifted by Diageo to Scotland's Garden Trust in 2003 for the purpose of developing the national garden.
Cherrybank and the six-acre Heather Garden, which was originally part of Diageo's Bell's office complex, were to be incorporated into the Calyx garden site.
The trust put forward an application to the National Lottery for £25m for the project but it was turned down in November last year.
The rejection left the existing gardens, which employs 13 staff, economically unviable.
Since the announcement that the gardens will close, a 3,000-signature petition has been handed in to Perth and Kinross Council.
Mr Miller has also urged locals to visit the gardens en-masse on Monday to show support.
But in a statement, Peter Fairlie from SGT said: "PKC needs a fresh and visionary approach at their helm if they want to take tourism and economic development seriously in Perthshire."
Mr Fairlie said that despite many approaches, the council refused to back the Cherrybank Centre.
He added: "PKC were asked finally on 14 December to support, at a very minimum, to keep Cherrybank open.
"This included the option to keep Cherrybank open at least until end October, at a cost of £76k, but they refused."
In response to the criticism from Mr Fairlie, council leader Ian Miller said: "It was a sad day when the lottery bid for the Calyx was lost, it is even sadder now to see those at the helm of that failed bid attempting to shift the blame for their failure onto others.
"I will not be responding to the allegations made in their statement, they can only be described as ludicrous and are therefore not worthy of comment."
A spokesman for Perth and Kinross Council added: "The council does not fund Cherrybank Gardens. Cherrybank Gardens is a private business and is not run by Perth & Kinross Council.
"At a meeting in December last year the SGT, without notice, put forward a request for £76,000 for Cherrybank Gardens.
"This meeting was called to discuss the future of the Calyx, not Cherrybank Gardens."