Staff working at the garden yesterday discovered four rose bushes had been jumped on, trampled and smashed, most likely by someone cutting through the garden from the Castle St bridge the previous night, botanic garden collections supervisor Barbara Wheeler said.
It was possible one of the bushes could be saved, but three others were damaged beyond repair and would have to be removed, she said.
They included two large 21-year-old bushes, one of which may yet prove irreplaceable, she said.
"If we can't get that old rose purchased through a nursery, then we've lost it forever if we can't propagate it from the one we've got here."
The damage comes after Dunedin City Council staff on Wednesday said they planned to increase security patrols, after an increase in drinking sessions and associated problems inside the garden this year.
Ms Wheeler said no rubbish, broken glass or other signs of partying were left in the garden yesterday, suggesting a drunken culprit was most likely taking a shortcut through the garden after gates were closed for the night.
The smashed bushes were part of the lower garden's popular main rose walk, and the damage would leave an ugly scar for the summer, she said.
"It is frustrating because you spend all your time growing these plants and then some ratbag comes along and just destroys all your work that you might have spent 20 years doing.
"You can't get that time back, so it is really frustrating.
"Once we pick up all the debris, it's going to be just a hole in the rose garden that will remain a hole all this summer. It just effectively ruins that display."
