Some apple growers in Essex County were likely sleep deprived Monday morning.
Environment Canada issued a frost warning Sunday night. Temperatures hovered around zero.
Leslie Huffman, an apple specialist with the Ontario Ministry of Agriculture and Food, said farmers would be up every hour checking on crops during cool spring weather.
"Anything below zero, and we're a little worried," she said.
Huffman said some farmers reported temperatures below freezing.
"Many of them have purchased frost fans and they were running frost fans from about midnight on last night," Huffman said.
Frost fans push warmer air above the orchards downward and raise the temperature at ground level.
"Sometimes raising it a little is enough to save the crops," Huffman said.
It won't be known for at least 48 hours whether this past weekend's cool temperatures damaged their crops.
Huffman said apples are just now coming into bloom. Some varieties are in full bloom, and those away from the lakes more advanced.
Last year, trees bloomed early after above-average March temperatures. Trees were in full bloom on April 12. A frost on April 29 that year destroyed a majority of the local apple crop.
A flash frost destroyed nearly 90 per cent of the provincial crop when temperatures returned to normal, according to the Ontario Apple Growers Association.
"We're in a more normal stage of development this year," Huffman said. "This is kind of a delicate time for us."