Cold weather blanketed California's Central Valley this weekend, but for local citrus growers sub-freezing temperatures were a welcomed change from the unseasonably warm December weather to-date.
Temperatures ranged in the high 20s to low 30s on Friday, Saturday and Sunday nights, which is ideal for most citrus varieties at this point in the season. Navel oranges and lemons are generally more cold tolerant than mandarin, or easy-peel, varieties such as Clementines, Murcotts, and Tangos, but with frost protection by wind machines the weekend temperatures proved favorable for all varieties. The cold weather will actually cause the maturation process of the fruit to slow, allowing for the fruit to store longer on the tree and maintain its flavor, external quality and color.
In Kern County, where much of the Central Valley mandarin crop is concentrated, temperatures hovered around 31 degrees the night of Dec. 18, which with the aid of wind machines is an ideal temperature point. Similarly, in Tulare and Fresno Counties temperatures were well within preferable ranges.
Most mandarin growers report running wind machines on average 16 hours this past weekend. Navel oranges, by contrast, can withstand cooler temperatures at longer durations. Wind machines were used on roughly one-third of the Central Valley navel crop — covering 44,000 acres — for an average of five hours on Saturday and Sunday nights.
Wind machines can raise temperatures as much as five degrees by trapping and circulating the warm air rising from the moist ground in the grove. Growers will irrigate in anticipation of cold weather to ensure ground temperatures are warm. When that warm air rises as temperatures cool, it is pushed downward by the wind machines.
California Citrus Mutual estimates Central Valley citrus growers spent a total of $25.1 million in frost protection this weekend alone to protect the region's $2.5 billion crop.