JOHNSTON, S.C. — Four generations of growing peaches in South Carolina have taught the Yonce family where to plant trees for the best crop, how to prune for the best yield and what to do in a late freeze to prevent a devastating frost.
But what the Yonces and thousands of other peach growers still don’t know is this: How does a peach know when the cold weather is over and it is time to grow?
A group of Clemson University researchers is trying to find the answer.
“It’s an interesting phenomenon,” Clemson plant biologist Doug Bielenberg said. “These plants count the cold hours and days. If it gets warm for a bit, they stop, and then they pick up counting where they left off.”
The concept is known in the plant world as chill hours. What Bielenberg is trying to figure out is how a plant has this memory and which genes control the process.
If scientists learn how to manipulate the peach’s chill hours, the research could be groundbreaking. By reducing the hours, plants could be grown in a large number of climates.
For peach farmers, it could mean getting larger, juicier varieties into stores faster, Bielenberg said.
Peaches are ideal for this kind of research because they have a fairly simple genetic structure and are closely related to a number of other fruits, such as berries, apples and plums, Bielenberg said.
Peach farmers are watching the research carefully. Blooms are just starting to come out on the earliest varieties, meaning Larry Yonce again will hang on to the weather forecast through April, when he can be sure freezing temperatures are over until the fall.
“The weather controls our destiny, basically,” said Yonce, who has been growing peaches for four decades. The family business is J.W. Yonce & Sons farm, founded by his grandfather in 1932 in Edgefield County.
Yonce’s 3,000-acre site is the second-largest peach farm in the second-highest peach-producing state in the country, behind California. The area produced cotton for decades before the boll weevil wiped them out. Farmers along the rolling hills of the ridge of South Carolina eventually turned to peaches.
The fruit was perfect for the area. Winter nights are cold enough for the chemical reactions that make peaches sweet, but not cold enough to kill the fruit as it grows. Peaches later need warm to hot weather to mature. That’s why Georgia joins California and South Carolina as the leading peach-producing states.
Research from Clemson and the University of Georgia has helped farmers considerably over the years. One of the Yonce farm’s best-sellers is a peach, developed through years of breeding, that doesn’t need as many chill hours, so it ripens in May, but it has the color, texture and sweetness of peaches that used to hit the market in July.
Even with all the science, there is still plenty of uncertainty in peach farming. Last year’s crop looked promising until a warmer-than-usual March and April left the fruit without enough chilling hours to reach its best taste and appearance.
In the family’s orchards, Chris Yonce points to blooms already on the tree. What should become a peach is already inside, no larger than an eyelash and about a quarter of the length. In about a month, roughly a third of the blooms will be removed from the tree by hand to maximize yield.
Yonce takes his knife and cuts open a bloom. The tiny fleck inside is black. That flower would yield no peach, but Yonce wouldn’t have known until after the pruning.
“Growing peaches is like legalized gambling,” he said.