Heavy frosts in Central Otago have struck the area's vineyards.

McArthur Ridge Vineyard manager Murray Petrie said this morning there had been four major frosts, lasting up to six or seven hours each, in the area since Saturday, with temperatures varying from -5 and -4 degrees

''Historically it's probably been the coldest spring of the last 20 years,'' he said.

A heavy snowfall on Friday meant there was more cold air mass circulating in the area, he said.

However, he was counting his blessings the vineyard, renowned for its pinot noir, operated an overhead water sprinkling system to help prevent frost damage - which had so far only been minor.

Sprinkling water onto the vines formed a thin layer of ice to protect from the frost, he said.

''Others that have had wind machines or helicopters  haven't come off so well.''

He was hopeful the weather would improve.

If the heavy frosts continued ''there'll be less grapes from the 2013 vintage'' but it was unlikely the area would receive another major dumping of snow again this season, he said.

Growers cross fingers Central Otago grape growers hope the worst of the devastating spring frosts are over, with overnight temperatures forecast to improve in coming days.

Unseasonably heavy frosts have forced growers to work up to eight hours a night to protect their crops.

Temperatures as low as -5 degrees Celsius on Monday and -4C yesterday morning came at a considerable cost, with early estimates suggesting as much as 1000 tonnes of the annual 8100-tonne harvest could have been destroyed.

Climatologist and frost specialist Stu Powell said the weather looked set to improve from tonight.

"We see a gradual warming. I think tonight (Tuesday) will be the last of the frosts. Tomorrow night (Wednesday) will be slightly warmer and the next night will be considerably warmer. I've not seen a season with as many frost events as this since 2005."

- © Fairfax NZ News

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