The English walnut, also known as the Persian walnut (Juglans regia), is grown almost exclusively in the United States within the borders of California. The state’s agricultural industry produces over 99% of the commercial domestic supply. The unique environmental conditions of California’s interior provide the specialized climate needed for the walnut tree to thrive and produce a high-quality kernel. The cultivation of this nut is a major agricultural activity concentrated in specific, fertile regions of the state.
Primary Cultivation Areas
The majority of California’s commercial walnut acreage is located within the Central Valley, which stretches approximately 450 miles through the state’s heartland. This immense valley is geographically divided into two primary growing regions: the Sacramento Valley in the north and the San Joaquin Valley in the south. These areas provide the expansive, flat landscape necessary for large-scale orchard operations and mechanical harvesting.
The Sacramento Valley is a major concentration point, with Butte and Sutter Counties consistently ranking among the top producers by acreage. Moving south, the San Joaquin Valley features a dense concentration of orchards in counties like San Joaquin, Stanislaus, and Tulare. These specific counties account for more than half of the state’s total walnut acreage. The Central Valley location offers access to necessary irrigation water and a climate that meets the tree’s precise seasonal needs.
Essential Climate and Soil Requirements
The geographical concentration of walnut orchards is tied to the tree’s requirements for both climate and soil composition. Walnut trees require a period of winter dormancy, satisfied by accumulating “chilling hours,” defined as the number of hours where the temperature remains below 45°F. Most common varieties need between 700 to 1,000 chilling hours to ensure proper bud break and spring flowering, a condition the Central Valley reliably provides.
Once the dormant period is over, the trees need a long, hot summer to fully develop and fill the kernels, thriving in temperatures between 75°F and 85°F. The soil must be deep, fertile, and well-drained, ideally a loamy composition that allows the extensive root system to penetrate at least five to six feet. Shallow soils or areas with high water tables are avoided because they restrict root growth and reduce the tree’s overall health and productivity.
The Annual Production Timeline
The yearly cycle of the walnut orchard begins in the winter dormancy period, when trees are typically pruned to manage canopy size and shape. As temperatures rise in the spring, the trees enter the bloom period, with both male catkins and female flowers emerging around April and May. Pollination is achieved through wind dispersal, and nut development takes place through the warm summer months.
Kernel development, where the nut meat fills the shell, occurs from mid-June through late July. Harvesting commences when the outer green husk, or hull, begins to split, typically starting in late August. Mechanical shakers are used to vibrate the tree trunks, causing the mature nuts to fall to the prepared orchard floor. They are then swept into rows for collection by specialized harvesting machines. This intensive harvest operation continues through late November.
California’s Role in Global Walnut Supply
The California walnut industry holds a dominant position in the world market due to its volume of production. The state’s growers contribute to a significant portion of the global trade, often accounting for more than half of the world’s exported walnuts. This scale of production makes the Central Valley a major player in the international agricultural economy.
The economic importance of the crop to California is considerable, generating over a billion dollars in value annually. Walnuts are one of the state’s leading agricultural exports, with a large percentage of the harvest shipped overseas to markets in Europe, Asia, and the Middle East. This strong export market underscores the consistent demand for the nuts produced in California’s fertile Central Valley.