Shelli Mears was out with the calves at her Hampden-Palmerston Rd property about 1pm, waiting for a stock truck to arrive.
Clouds darkened, a flash lit up the sky and she heard an "enormously loud crack''.
"The calves were very upset. They all jumped in each other's pens.''
Her instinct was to check inside the house as her pet dogs were "terrified of lightning''.
There she smelled smoke and called emergency services.
When outside, Mrs Mears followed scattered splintered pieces of wood into her garden to find the oak tree had been deeply pierced by the strike.
It had damaged the tree right to the core.
The oak would likely need to be safely removed, she said.
"It's a real icon in the garden. It's sad that it's got to come down, really. It's going to leave a big gap.''
The tree was thought to have been planted as part of landscape gardener Alfred Buxton's design for the garden in the early 20th century. At that time, Buxton was one New Zealand's most prominent garden designers.
"I hope we can find a use for it. It would be a shame if it all had to be firewood'', Mrs Mears said.
The lightning strike may have also affected underground cables as the house's jack points were blown out of the wall and fuses were blown.
One of her dogs was too scared to come back to the house, she said.
"We heard another neighbour lost electricity. There were a few more cracks of lightning which got further away.''
Palmerston volunteer fire brigade station officer Craig McCaw said a crew looked around the property, but there were no obvious signs of smoke, so no more attention was needed.
An arborist was scheduled to assess the tree yesterday evening.
