The National Weather Service in Hanford, CA, has issued a hard freeze watch for the central and southern San Joaquin Valley of California effective Wednesday night, Dec. 4, through Friday Morning, Dec. 6. Low temperatures are expected to range from 22 to 27 degrees Fahrenheit in most rural areas, which is cold enough to cause damage to citrus crops.
While most citrus groves in the valley are grown up against the eastern foothills, where they have good cold air drainage and are not likely to get as cold as some spots in the valley floor, growers were taking steps and making preparations Dec. 2-3 to protect the crops from freeze or to minimize any damage that might occur.
About 85 percent of the winter citrus crop in the valley, including Navels and Mandarins, remained to be harvested and was at risk of freeze damage.
Bob Blakely, director of industry relations for California Citrus Mutual in Exeter, CA, said Dec. 3 that fruit damage could occur when temperatures get below 27 degrees and remain there for several hours.
"We don't think it is going to get that cold, but there is one forecaster out there that is predicting it down that low," said Blakely. "We will see who is right."
In any case, growers take no chances, and "the preparations are the same," he said. "They are preparing for a potential hard freeze."
Actually, some sub-freezing temperatures can be beneficial to the citrus crop, Blakely explained. "We need some of this to really harden the fruit off and harden the trees" so they are better able to take even colder weather later on. "We don't need long durations in the low 20s, but we can certainly use some upper 20s," he said.
The trees themselves can take quite a bit of cold without being damaged. They will generally do OK unless temperatures drop into the low 20s or the teens and stay there "for quite a period of time," he said. "Even then, they can be quite resilient.
"In 2007, we thought we had a pretty bad freeze, and the trees came back" with a crop the next year, he added.
The worst freeze in recent memory was in 1990, when temperatures in the Citrus Belt dipped to 11 or 12 degrees in some spots. That did damage to some lemon trees, which lost two crops -- the on-tree crop and the following year's crop due to damage to fruiting wood.
However, the orange trees "came back fine," he said. "We had an orange crop the next year. It was a light crop, but we had a crop. So the trees can take quite a bit."
In an effort to prevent or minimize damage to citrus on the tree, growers are "running water, getting some moisture in the ground," Blakely said. "There hasn't been much rain this fall, so the ground is dry. Growers want to have the ground wet so that it will absorb better during the day and release it at night."
The growers are also "checking their wind machines, making sure everything is ready to go," he said.
Wind machines in the orchards can pull warmer air down from higher altitudes and warm the groves by a couple of degrees or so, which can often be enough to prevent damage.
Should damage occur, packinghouses have equipment available, some utilizing sophisticated technology with electronic sensing equipment, to sort out the frost-damaged fruit and keep it out of the pack.