Mr Le Roux, who moved from South Africa with his family a year ago, said his first impression was it was a "wonderful" facility.
The gardens, which were officially opened in 1876, were last week designated by the New Zealand Gardens Trust as a "garden of significance".
The formal assessment is made every three years and it is the second time they have been recognised as significant.
The next step is to be recognised as nationally significant and, ultimately, as of international significance.
Trust member Gordon Collier said the old trees and historic nature of the gardens were "quite outstanding".
"They are well up to the standard of other provincial public gardens and the staff there are doing a very good job," he said.
Improved maintenance since the last visit was key, Waitaki District Council property parks manager Dougall McIntyre said.
The "bones" of the garden were excellent and it was now a matter of refining it.
Major issues needing to be addressed were accessibility and succession planning for specimen-tree replacement, he said.
Mr Le Roux praised the 3.5 full-time staff, who assisted him "tremendously" and gave that "little bit extra" support and devotion, which he believed was the gardens' secret to success.
Staff were constantly getting compliments from visitors, with people saying that it was amazing a small town maintained such an asset.
There were many different garden experiences within a compact environment, he said.
The trust's assessors were particularly impressed with forward planning for developing the gardens, Mr McIntyre said.
Land Landscape Architect of Queenstown had been contracted to do a master-planning exercise for the next 30 years and site analysis had recently started.
There are 41 public and private gardens throughout the country that have been assessed as significant, 30 of national significance, four of international significance and 61 registered gardens.
A bequest of $92,875 to benefit the Oamaru Public Gardens will be used for a project that would not otherwise have been funded.
The late James Wilson McCone, who made the bequest, died the day before his 80th birthday in 2007.
His sister, former borough councillor Shirley Behrent, will be on the committee convened to select the project.
She said she and her brother grew up playing in the gardens.
"We took our lunches there for an outing and played on the swings and slides. He loved the gardens and being a bachelor with no family to provide for, he wanted to give something back to the town."
Waitaki District Council property parks manager Dougall McIntyre said the council was very grateful for the bequest.
"A menu of projects for funding will come out of the forthcoming development plan and once the menu has been released we hope other people may wish to put a project forward and finance it," he said.
