With a frost warning in effect in parts of Canada, an Ottawa area farmer reportedly sent a helicopter to hover over his apple orchard overnight Monday in an unusual effort to save his crop.

Temperatures in the Ottawa region fell to -2 degrees Celsius (28 Fahrenheit) at about 3 a.m. (0700 GMT) early Tuesday morning.

Phil Lyall of Mountain Apple Orchards, about 60 kilometers (37 miles) south of Ottawa, told public broadcaster CBC he paid thousands of dollars to have a helicopter fly all night over his 10,000 trees in order to push rising warm air back down and keep temperatures on the ground above freezing.

It was the second time in two years that he'd tried it, after hearing that fruit growers in Argentina, New Zealand and elsewhere were doing the same in similar circumstances when their crops were threatened by cold.

Last year, he recorded a six-point jump in temperatures in his 25-acre orchard, from -3 degrees Celsius (26 Fahrenheit) to 3 degrees Celsius (37 Fahrenheit).

Lyall said his orchard might lose only 10 percent of its apples when temperatures drop to zero degrees Celsius (32 Fahrenheit), but a night at minus two can kill 90 per cent of the crop.

"The MacIntosh (apples) are just about in full bloom, some of them already are, and that puts them at their most susceptible stage right now," he told CBC.