Some southerners call it blackberry winter.

It’s that last cold snap before spring, when cold weather rears its head one last time before giving way to warmer temperatures in the slide to summer.

Just a week ago, azaleas across the Golden Isles blossomed like bursts of magenta and white fireworks. The warmer than average winter is to blame for this year’s unusual plant growth, said Don Gardner, an agricultural and natural resources agent with the Glynn County Cooperative Extension.

“Plant development depends on temperature and requires specific amounts of heat to develop from one point of the life cycle to another, such as from seeding to harvest stage,” said Gardner, who works for the University of Georgia’s College of Agricultural and Environmental Science.

Certain plants need various amounts of hot and cold weather to move to the next phase of their growth, he explained.

“There are stone fruits, like blueberry, or peaches, and they need a certain number of hours below, say, 50 degrees, or below 40 degrees,” he said. “It varies for different crops.”

Farmers and agriculturalists measure temperature patterns in chill hours and heat units, Gardner said. Different species need varying numbers of hours below a given temperature to produce fruit.

For example, the Alapaha rabbit-eye blueberry, which can be grown in South Georgia, needs between 450 and 500 hours of yearly growth at temperatures below 45 degrees.

“You can hold on to these hours unless you get a day above the set temperature, and then the number of hours you stay above that temperature have to be subtracted from the total,” Gardner said. “So, it can wipe you out.”

Although it may be chilly outside this week, overall a lack of cold weather this winter has complicated the season’s blueberry production, he added.

“It’s been so warm that we’re not getting the number of chill hours we need for blueberries,” Gardner said. “We’re also looking at erratic fruiting. Instead of having the crop come in the way we anticipate, we now have folks out there spraying (insecticides).”

Increased use of insecticides and fungicides can drive up costs and cut into farmers’ already thin profit margins, Gardner added.

The mild winter has made it a challenge for blueberries to fruit this season, Gardner said. Still, many tolerant varieties across South Georgia have done alright, but this week’s cold weather could complicate things.

Georgia leads the nation in blueberry production. State Agriculture Commissioner Gary Black is concerned the falling mercury could harm this season’s blueberry crop, which is almost ready for harvest.

“They’re telling me this morning that 60 percent of the rabbit-eye blueberries and then even some portions of the highbush could get pounded tonight,” Black told the Atlanta Journal-Constitution on Wednesday.

Gardner said this winter’s mild temperatures could have long-range impacts for the rest of 2017.

“Another thing we’re seeing this year is more problems with insects,” he said. “Because it didn’t get cold enough, they didn’t get killed off.”

Uncontrollable weather-related factors have tested South Georgia farmers this year, Gardner added.

“There are a number of factors that make an impact,” he said. “The biggest gamblers are not in Las Vegas. They’re on the American farm.”