Get out the extra blanket, winter is about to make its presence felt in Northland after a summer that seemingly went on forever, with colder temperatures and the possibility of ground frosts across the region from today.

Northland tamarillo, potato and courgette growers expected to have a nervous night as a cold snap could have devastating consequences for their crops, with the fruit particularly susceptible to frost.

MetService meteorologist Elke Louw said Northland had seen some great autumn weather with highs of up to 22C on Saturday and lows in the teens, but that was about to change as the cold southerly front bringing sub-zero temperatures to the South Island headed up the country.

Ms Louw said this morning would be the coldest of the year so far, with a low of 4C-5C expected and a high of only 14C.


"You will feel the change from [Tuesday] as the cold southerly heads north and a lot of people will wake up to the coldest day they have felt so far this year," she said.

"Winter seems to be working its way up to you, though your maximum temperatures could still be 18C or 19C for the next week or so. You may also have some ground frosts in sheltered areas."

Ms Louw said with winter fast approaching, Northlanders should cherish any fine weather they got.

Maungatapere horticulturist and chairman of the NZ Tamarillo Growers Association Craig Watson is one of several growers hoping the chill will not affect his tamarillo crop.

Mr Watson has been harvesting his trees for the past six weeks and, with another four or five months of harvesting to go, knows that a frost at the wrong time can be devastating.

"If it's a light frost the leaves can fall off, but it it's a heavy frost the leaves and all the fruit can fall off ... and that's not good," he said.

Mr Watson said covering trees with a blanket to keep the frost off was only really practical for small, home growers, but he had installed a hail cover over his crop to prevent it being damaged.

"We'll soon find out if it works, I suppose. We don't want anything bad happening at this time."

He was aware of one grower who had bought a portable Tow and Blow wind machine to guard against frost. The machine works by circulating air around the plants to prevent a frost.