The PN has called for an investigation into the mismanagement of three green walls that were left to rot after they were installed at a cost of €600,000.
Describing the project as a "grotesque" symbol of the government's "greenwashing" and "monument to Labour's failure", the Opposition said those politically responsible should be held accountable.
Times of Malta revealed on Sunday that the vertical gardens in Mosta, Marsa and Corradino industrial estates will be scrapped after government agency INDIS said the cost of watering them outweighed the environmental benefit.
The walls, unveiled by economy minister Silvio Schembri and then-environment minister Aaron Farrugia in 2021, appear dead with government agencies arguing over who was responsible for their upkeep.
In a statement on Monday, the PN said it was another example of "staggering incompetence and blatant squandering of taxpayer money".
It said the costly promises of urban beautification had been exposed as "hollow political stunts" and highlighted "the poor planning and lack of feasibility behind the project".
The green wall in the Marsa industrial estate was the most expensive, costing almost €306,000 to install, while almost €163,000 was spent on the structure in the Corradino industrial estate and €128,000 at Mosta Technopark.
"The real tragedy of this fiasco is what could have been done with these wasted funds," said the statement signed by environment spokesperson Rebekah Borg, creation of new spaces spokesperson Bernice Bonello and climate change spokesperson Eve Borg Bonello.
They pointed out that with €600,000, the government could have planted thousands of trees instead of throwing away public money on "ill-conceived, unsustainable projects" that are "monuments to Labour’s failure".
It accused the government of being more interested in "flashy announcements" and photo opportunities than ensuring projects were sustainable.
At the time of their installation, the walls comprised almost 40,000 plants but a visit by Times of Malta to the three sites showed they appeared brown and dried or were already being removed.