Almost all (99%) of U.S. walnut growers are located in California. Approximately 4,000 California walnut growers produce over 500,000 short tons of walnuts annually. Over 180,000 acres in the state are currently planted in walnut trees.
Walnut growers typically plant trees from twenty-five to thirty-five feet apart. It takes approximately four to five years of growth before orchards produce their first yield. To ensure healthy growth, walnut tree cultivation requires constant attention during every step of the process. This includes pruning, spraying for insects, fertilizing, mulching, and irrigation. Typically walnut orchards have a productive life of thirty-five to forty years.
Harvesting begins in early to mid September when the protective green hulls split, indicating that the nuts are ready to be removed from the trees. Harvesting operations are largely automated. Mechanical shakers are used to remove the walnuts from the trees. After they fall to the ground, the walnuts are swept into wind rows to
allow mechanical harvesters to pick them up for cleaning and hulling. Harvesting can continue through November.
Although many varieties of walnuts are grown in California, six varieties account for over 75 percent of total production. Those varieties include Hartley, Chandler, Serr, Vina, Tulare, and Howard.
There are three primary regions in California where walnuts are grown:
• Sacramento Valley – includes area from Yuba City (south) to Cottonwood (north)
• North San Joaquin Valley – includes area from Turlock (south) to Stockton (north)
• South San Joaquin Valley – includes area from Tulare (south) to Turlock (north)
Because of the Delta breezes that flow from the San Francisco Bay during the summer nights, the nut kernel color from the North San Joaquin Valley region is typically the lightest of the three major regions, making these nuts highly sought after.
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