Director Wolfgang Bopp told Morning Report the sheer number of birds was the problem.
"They're large birds and for any large animal, what goes in the front, comes out in the back and that's quite a lot.
"If we only had a couple of them, five or six across the gardens, that wouldn't be a problem."
He said picnic-goers should be able to put their rug on the lawn without having to contend with a lot of geese faeces.
The black cut-out wolf and coyote decoys with white eyes were placed around the gardens by rangers.
There is writing on the decoys to identify they are being used for predator control.
Bopp first heard about the decoys from Clearwater Golf Club.
It started placing wooden cutouts of wild coyotes on the course in 2021 to scare off Canadian geese and unwanted "foreign bogeys" that invaded the fairways.
Bopp is hoping the decoys have a similar impact at the Botanic Gardens.
"They actually gave us one of the decoys which we then just traced over and cut out our own ones," he said.
"[The ranger] will move them every day and he's actually going as far as barking at the geese at the same time.
"Now he's finding that as soon as they see him they think: 'Oh right, ok, let's move on'."
The decoys did not work 100 per cent of the time, but Bopp said they appeared to be keeping the geese off the lawns.
"So far the wolves, a natural predator of geese, are working well.
"Our rangers often move them around so the geese don't get used to their presence.
Bopp reminded visitors not to "feed the geese".
"It's bad for the environment, spreads disease, and creates stress and competition among the birds.
"We've also had our wolves stolen and injured so please let our team know if you see any suspicious behaviour."
