Ministers claim the display will help educate the public on the dangers of pests and diseases which threaten Britain's flora and fauna.
But one former Department for the Environment, Food and Rural Affairs (Defra) minister condemned the "cock-eyed" plan at a time at a time of austerity and deep public spending cuts.
The £95,000 cost for the design and build at the RHS Chelsea Flower Show in May is largely coming from the coffers of Defra, which suffered some of the deepest cuts of the coalition austerity programme. Funding is also coming from the Forestry Commission, the Welsh and Scottish governments and the Timber and Pallet Federation.
An award-winning designer has been hired by the Food and Environment Research Agency to highlight the issue of plant disease "in a way never seen before".
Publicity material suggests a sunken garden featuring "quintessential native trees and lush shade-loving planting" will be "starkly contrasted with sinister and shocking elements". These include "an avenue of dead trees" and an "ominous" pool with an island holding a single sapling.
Former forestry minister Barry Gardiner, who unearthed the costs in parliamentary questions, condemned the extraordinary use of public money.
The Labour MP said: "I love Chelsea Flow Show, I love all flower shows. But the idea that we are sacking 60 people in forest research and spending £95,000 on a show garden for two weeks at Chelsea trying to communicate to people the danger of forest disease strikes me as the most cock-eyed, inverted, upside-down, cart-before-horse proposal I have ever heard."
Environment Minister Richard Benyon claimed the garden will "deliver strong messages to the public on the scope for behaviour change to make a significant impact on the prevention and identification of pests and pathogens that could affect our trees, including the threat from non-native species".
The show garden is "just one element of a campaign of public and stakeholder communication regarding tree health and plant biosecurity", he added.
