Nervousness was only natural, Ardern said before Hosking cut in with a question.
"What about outfit?" he asked.
Ardern said she'd started considering colour schemes yesterday, before questioning the broadcaster whether he'd be asking English the same question.
"Are you asking Bill that question too?
"I want it framed in exactly the same way," she joked.
Hosking assured Ardern he would be, saying there would be "balance up the wazoo".
After the interview English was asked by reporters what he would wear for tonight's debate and said: "I'm going to wear a suit and tie. It might be a new tie, yes it will be a new tie, not a new suit."
In the Newstalk ZB interview Hosking also asked Ardern about Labour's newly announced policy, which is promising students one free year of tertiary education from the start of next year.
The no-fees policy will extend to two years by 2021 and three years by 2024.
Labour will also increase student allowances by $50 to $220 a week and reinstate allowances for postgraduate students and those studying for more than seven years.
Ardern said the offer was not only focused on university - it was also targeting people who were training for practical skills.
"This is transformational for the New Zealand economy as much as it is for education."
The $16 billion of debt carried by Kiwi graduates was a barrier Ardern said she wanted to remove.
"That's affecting everything. It affects their ability to get into home ownership, it affects them delaying having kids."
The pair also discussed New Zealand First leader Winston Peters' plan to move Auckland's port to Whangarei.
Ardern said the "car park" on the city's waterfront was a problem that has needed to be dealt with for some time.
An hour before the debate starts tonight, the results of the latest Colmar Brunton poll will tell Ardern whether the surge in support for Labour has continued, slowed or stopped.
