As a bout of cold spring weather dropped temperatures in the Philadelphia region below freezing overnight Wednesday, fires dotted Linvilla Orchards in Middletown Township, Pennsylvania, as workers tried to save the peach tree crop.

In Philadelphia, the mercury dropped into the low 30s with a breeze making it feel like the high 20s. It was even cooler out in Delaware County — and dangerously below a threshold where Linvilla could lose the whole crop, farm manager Norm Schultz said.

That happened five years ago, and it's something they don't want to happen again.

"If it gets down below 25 degrees, we could actually lose most of the peach crop tonight, so we're trying to burn some fires," Schultz told CBS News Philadelphia. "The main idea is to produce smoke to get a blanket of smoke over the orchard and to catch the heat coming up out of the ground and just get us a few degrees to get us through the night."

Thermometer readings showed the temperature was 24 degrees at ground level but a little warmer at the height of the tree canopy.

He said the fires were started using dry wood and plywood, and then green wood was added on top to produce the smoke.

Farmers are keeping their fingers crossed that the overnight effort worked. It won't be long before they know. By around noon, they can check inside some of the peach blossoms to see if they are green, meaning they're healthy, or black, meaning they did not survive.

This is only the third time in the past 30 years that Linvilla has had to warm the orchard like this.

While April 9 is late to have temperatures this low (and this is the coldest morning in a month), it's far from the latest "final freeze" we've ever had – that was May 11, 1966, according to our NEXT Weather team.