"When I saw the wandering jew, I thought how do I turn a blind eye to this?"
And his painstaking work has made a huge difference.
"It's very special to see ferns growing up along the paths with the wandering jew gone," he said.
Rose Karena said she first met Wainwright years ago out on the gorge track clearing old man's beard at the time and other miscellaneous weeds.
"I think he's one in a million and we're lucky to have him out there," she said.
"He also clears up the ivy around Woodville where he can and he gave me tips on how to get rid of the ivy at kohanga. You'll find him here, there and everywhere."
Susannah Robertson said she ran into Wainwright and his wife Rosalie clearing dangerous trees from the totara walk, and weeding.
"What legends," she said. "We need more like him."
When he first began Wainwright was overwhelmed by the enormity of the challenge of eradicating wandering jew, but on his knees, with bare hands, he's pleased with how much he can clear in an hour.
However, he needs to revisit most areas three times to wipe the weed out.
"Sometimes there are roots underground, which have popped up next time you visit and other times, the pieces of weed are so small, I miss them," he said.
However, Wainwright had to take an 18-month break from his volunteer work after a devastating heart attack and has been back battling the weeds for just six months.
"My wife Rosy persuaded me to take a walk in the bush with her when I was recovering. I didn't want too because I knew it would break my heart," he said.
"But that was just burying my head in the sand. I saw the track was only being kept open by the feet of trampers and it was the kick in the pants I needed to get out and begin my work again.
"A poster in the coronary ward said, 'activity is the key to recovery,' so I'm back on the warpath of wandering jew again."
For Wainwright, a self-proclaimed eco-warrior, this is a very specialised job.
"You have to work on your knees all the time," he said.
"And you need to keep your eyes peeled, just in case there are tiny ferns in the area where you are pulling weeks. But sometimes the wandering jew is so thick you just have to pull and pull.
"It's detailed work because you want to eradicate the wandering jew, but leave the baby ferns."
And Wainwright's reward is seeing giant maidenhair fern regenerating, with the gorge the only place where it grows in the wild in New Zealand.
Wainwright stores the wandering jew in large 166 litredrums and black bags.
Visitors in the bush may see those black bags in the bush, but they are not household rubbish being illegally dumped, he points out.
"After a time the wandering jew will die and the drums and bags can be emptied and
refilled. The dead plant material rots down into the ground to help nourish the bush. I like this way of fighting wandering jew because it gives me very enjoyable light exercise and achieves results without poisonous sprays," he said.
But, Wainwright admits, there will come a time when he won't be able to continue his volunteer weed-clearing.
"I've had just two offers of help over the years," he said.
"But I'm hopeful Horizons Regional Council may have a solution to the wandering jew problem eventually."
