RHS Wisley is home to seven national plant collections
Proposals to build compost sites near the Royal Horticultural Society (RHS) garden in Surrey have led to concerns that plant diseases could spread.
The Composting Company has applied for permission to site a new facility close to RHS Wisley, a "national treasure" with seven national plant collections.
The RHS complained that their gardens are down-wind of the compost site and plant pathogens could be spread.
But the developers said the process was "natural" and would cause no harm.
Roger Hughes, from The Composting Company, said: "It certainly is bigger than your home composting bin, but the process is exactly the same.
"It is taking the kind of material that you and I discard on a daily basis and keeping it out of landfill.
"In landfill it produces methane which is a very powerful greenhouse gas and contributes to climate change."
He said the Environment Agency and Defra had told them there were no risks.
"There is not a single case that I'm aware of where an industrial composting plant has been shown to cause problems with the transmission of plant disease," Mr Hughes added.
The RSH commissioned an independent agency to asses the proposal and was told the site posed a "genuine risk".
James Rudoni, from RHS Wisley, said: "The RHS is a huge advocate of composting in general, but what we have is industrial scale composting right on our doorstep and the garden is going to be put at risk by plant pathogens.
"The issue is the scale of it. And secondly, we don't know where this compost is coming from, whereas everything we compost on site we control."