Colin and Donna Craig-Brown have named the spud Doug. Colin was digging up weeds in the garden when his hoe hit a large mass in the soil.
"I got the fork in and jabbed it out of the ground and [thought], 'Holy snapping turtle teeth what's going on here?' Colin told Sky News.
To preserve the potato and to stop it from drying out, they're keeping it in plastic bags, but continue to dress it in a hat when it's on show.
“I said to Donna this must be one of those white kumara (sweet potato) that we grew,” he told Stuff website, “because some of them just grew massive here.”
The pair have grown very fond of the giant starchy tuber.
“We put a hat on him. We put him on Facebook, taking him for a walk, giving him some sunshine,” Colin told the NZ Herald. “It’s all a bit of fun. It’s amazing what entertains people.”
As of 2011, the heaviest potato in the world was found in Britain in 2011 and weighed just under 5kg. The couple have reached out to Guinness World Records and are waiting to have Doug recognised as the new record holder.
They aren't sure exactly when they last planted potatoes in their garden, but estimate it was two or three years ago. Colin speculated that Doug self-seeded.
“It’s a mystery to me,” Colin said. “It’s one of nature’s little pleasant surprises.”
The couple are now considering turning the potato into vodka.