Donna and Colin Craig-Brown of Ngāhinapōuri have named their 7.9-kilogram potato 'Doug'.
The Craig-Browns had no intention of growing a large potato, Colin tells Jesse Mulligan. Doug was just "one of nature's pleasant surprises".
"I had no idea he was growing there and I don't know how long he was there because I was walking over top of him all last cucumber season.
"It's just one of life's happy little moments, you know? Mother Nature has just bestowed this glory upon us."
Doug was discovered a couple of months ago when Donna and Colin were cleaning up their vege patch for spring planting, he says.
"I wasn't sure what we were seeing. Was it a kūmara? Was it some big fungus growing out of the ground like a monster truffle or something? I didn't know what he was till I jammed the garden fork into him and dragged him out of the ground and gave him a bit of a scratch and a poke and tasted him. I said to my wife 'look, it's a dirty great big potato'.
"There was nothing gentle about his coming into the world, I tell you.
"He looked like some horrid gnarly thing that you wouldn't want growing anywhere on yourself. Ooh, nasty looking thing.
"Poor old Doug. He wasn't standing up to this global warming stuff. He was growing mould… the lady from TV3 reckons he smells like sardines."
After Doug was hosed down and washed with Janola and fungicide, he was put in the freezer where he's lost a kilogram in 10 weeks.
The current world record for a potato is 4.9kg and Colin is waiting for confirmation from the Guinness Book of World Records Doug is the biggest ever.
Then, once "the kerfuffle" is over, Colin plans to turn him into vodka.
"We'll have a wake for him and we'll all toast Doug with the vodka that I'm going to make out of him.
"I think the only thing he might be good for is brewing, rather than chewing."