It's the hottest day of the summer so far when I meet Tom Wichman. He's standing in the shade of a pair of scrappy trees - a pohutukawa and some sort of pittosporum - and he's using the gravity feed from a small plastic drum of water hoisted into the branches to dribble water on watermelon seedlings.
They're in little trays that he found in an inorganic rubbish collection and their little heads are already sprouting above the dense black soil.
"These things cost $2 each at the garden centre," he says. "I grew them from watermelon seeds. There's 300 here; that's $600 worth." He bursts into a booming laugh at the very idea.
Wichman, who hails from Rarotonga in the Cook Islands, is a regular presence at the Mangere Community Gardens, which overlook the car park at the Mangere Town Centre. In the cool of the morning and the early evening you'll usually find him there, offering the dozen or so fellow gardeners seedlings, equipment and advice.
The large plot is lush with life: beans snake up bamboo tripods; tomatoes are trained on to makeshift trellises of plastic mesh; pumpkin, cucumber and silverbeet flourish; the corn looks ready to pick. Half of the area is devoted to raising kumara seedlings, an initiative by an enterprising local Tongan fellow who pays for the ground by handing over a quarter of his crop.
The gardens are on land belonging to the Mangere Community Health Trust, which runs a medical clinic next door. But in this soil, Wichman is running a health enterprise of his own. He comes with impressive credentials: the first director for renewable energy in his homeland, which aims to be entirely solar- and wind-powered by 2020, he established hydroponic gardens on the sandy outer islands that were so successful they now sell surplus crops to crews of fishing boats.
But it was a more personal mission that brought him to this garden: "I was a sick man," he explains. "I was obese, diabetic, I had high blood pressure."
It seems hard to believe of the lithe and lively 73-year-old who is showing me around, but the undertaking plainly agrees with him.
"When people come here and start a garden, I tell them that when you are weeding or working the soil, you earth your body and you take the stresses out.
"So the benefit is not just eating the plants with no spray; you also get the benefit from the ground.
"If people come I will show them what to do, help them prepare the ground and they can do it. They get so excited and then they go home and dig a patch."
At less than a year old, these are among the newest community gardens in the area. A Google search throws up a couple of dozen results between Ranui, Manurewa and Albany, but John Darroch, who was instrumental in getting the Mangere project off the ground, says he is aware of at least 10 in Mangere alone.
"If you drive round, you see patches dug up all over the place," he says. "The number of people who are producing serious amounts of food in South Auckland is quite remarkable."
Darroch, a 24-year-old with a diploma in sustainable horticulture, says the place was "waist-high weeds" when he first saw it. "It was quite daunting but we organised a working bee and got the first few terraces dug up and it snowballed from there."
He describes himself as a social activist whose "main motivation is passion for social justice".
"I was born in Mangere and I've lived here most of my life so it's very local to me," he says. "On my street we have people living in garages and kids are eating really appalling food. Gardening is a way of connecting them to good-quality healthy food. Clearly that needs to go hand-in-hand with wider structural change in the economy but it's one tiny part of the jigsaw puzzle."
Darroch says that a couple of hours' work a week is all it takes to grow a family's vegetable needs. But there is a less tangible benefit in the sense of autonomy it confers.
"I don't think you can underestimate the value of getting your hands in the dirt and working alongside other people on something that is communal in nature. So much of what we do is competitive and individualistic."