The Future of Walnuts In the United States
By Peter Croce
October 22, 2026
5 MIN READ
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Warm, dry summers and cool, wet winters in California’s Central Valley nurtured walnuts for centuries. Trees rested in the winter, buds bloomed in the spring, and nuts developed in the summer. Farmers reaped consistent and abundant harvests in the fall.
In the 20th century, the area’s agriculturally ideal conditions inspired investment in large-scale water management projects to enable commercial cultivation in the valley.1 University agricultural innovation created a high yield walnut breed2 and walnut exports grew rapidly to become globally significant.3 The valley now grows about half of international walnut trade and virtually all (over 99%) of U.S. production.4,5 But as the climate becomes hotter and more unpredictable, growers are sounding the alarm. The future of California’s walnuts will again depend on investment and creativity.
“We are seeing volatility in weather patterns,” says Aaron Martella, President and CEO of Grower Direct Nut Co., a company that grows, packs, and ships California walnuts. He points to heat, drought, and loss of cool winters as significant climate pressures that have already damaged crops, causing bad harvests and financial stress.
While most areas in the valley experienced only a few weeks of very hot days in the past, many are already seeing more. Jared Britschgi, Vice President of Purchasing at Pearl Crop in Stockton California, emphasized an important temperature threshold for walnut trees. “Ninety-five degrees doesn’t bother me. It’s when we are 100-110°F that makes things harder to manage. It causes more stress to the tree and increases mite pressures which can hurt foliage and cause more sunburn.”
The map above shows the number of days above 38°C (100°F). On the left, the climate 1970–2000 (0.5°C above pre-industrial global average temperature) shows most areas in the valley experiencing fewer than a month of days above 100°F (38°C) in an average year. The climate expected within about a decade is on the right, with most of the valley showing over a month of days above 100°F (38°C) in an average year.
“When you combine high temperatures during nut fill, poor chill hours along with decreasing water quality or just the water limitations from SGMA” (the Sustainable Groundwater Management Act), Britschgi added, referring to the rules governing how much of the increasingly-scarce groundwater farmers and others in the region can use, “crop quality can drastically change in a matter of days.”
Adapting to changes
Growers have ideas for adaptation that could support prolonged walnut cultivation in the valley. Potential options include different cultural practices, infrastructure investments, and the development of new walnut varieties that are more drought-tolerant and require fewer chilling hours, a term that refers to the annual number of hours between 32 and 45°F (0 and 7°C) required for many fruit and nut trees to produce harvests.6 But growers are squeezed: while climate conditions and crop quality are degrading, investments in adaptation are often costly.
Britschgi lays out the challenge: “The difficult part is that implementing adaptation practices requires money, and, in the last several years, walnut growers haven’t had great returns to invest back into their orchards.” Martella adds that their “cultural practices are adapting” but it has been “difficult as there is only so much you can do with permanent crops and finances that have been very limited at the farm level.”
“It is not any one thing that growers do to adapt,” Britschgi said. “It is a bunch of little things in the hopes that it creates a better outcome.”
Looking to the future
With growing conditions eroding, California’s future as an abundant source of walnuts is uncertain. Growers’ expertise combined with maps of future climate conditions together offer an opportunity to look ahead and prepare. Growers already understand which thresholds matter for certain walnut trees, like the number of days exceeding 100°F or the number of chilling hours. Combining this industry knowledge with tools showing how these conditions are expected to change in near-term and potential-future scenarios, like the Probable Futures climate maps, can inform the adaptation process.
While adaptation to these scenarios will require creativity and investment, the costs of doing nothing are clear to growers. Britschgi puts it plainly. “If the industry doesn’t evolve with the times there won’t be one for much longer,” or at least “much smaller than it is now.”
Sources:
- https://walnuts.org/about-walnuts/history/ ↩
- https://chandlerorchards.com/chandler-walnut/ ↩
- https://walnuts.org/news/why-the-board-and-commission-are-important-to-the-california-walnut-industry/ ↩
- https://walnuts.org/about-walnuts/history/ ↩
- https://www.nass.usda.gov/Statistics_by_State/California/Publications/Specialty_and_Other_Releases/Walnut/Acreage/202405walac.pdf ↩
- https://oehha.ca.gov/climate-change/epic-2022/changes-climate/winter-chill ↩
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