The threat of frost has forced apple growers near Kemptville, Ont., to take the unusual step of flying a helicopter over their orchard to keep their trees warm.

The temperature in the Ottawa region dropped to -2 degrees Celsius at about 3 a.m. early Tuesday morning and a frost warning remained in effect Tuesday.

Phil Lyall of Mountain Orchards near Kemptville said while an orchard might lose only ten percent of its apples when temperatures drop to zero degrees Celsius, a night at minus two can kill 90 per cent of the crop.

"The MacIntosh, they're just about in full bloom, some of them already are, and that puts them at their most susceptible stage right now," Lyall said.

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Eastern Ontario apple growers have hired a helicopter to fan their fields when frost threatens. (Submitted photo)

Last year, when temperatures went even lower, Lyall tried something new that literally saved his apples.

Helicoptor pushes warm air down

He and his partner Bob Hobson paid to have a helicopter fly over their fields and push warm air down to his crop.

The helicopter, flying at about the height of a five-storey building, essentially acts as a giant fan, said Hobson.

"He circled the orchard and he went over our weather recorder, and the temperature went from minus 3 to plus 3 instantaneously," Hobson said.

The two used the helicopter again overnight Monday, paying to have a helicopter from Montreal come and perform the same duty.

The helicopter idea has been used by fruit growers from Argentina to New Zealand, but is less common here. It's not cheap, say Lyall and Hobson, but they say it has been worth it.

"I'd buy a helicopter tomorrow but Philip won't let me," joked Hobson.