Walnuts trace their origins to Central Asia, where they survived the last ice age in isolated stands stretching from western China through the Caucasus region. From there, ancient traders carried them along the Silk Roads and the Persian Royal Road, spreading them across continents over thousands of years. Today, China and the United States dominate global production, and the walnuts you find in grocery stores are almost certainly one of two species with very different histories.
Ancient Roots in Central Asia
The common walnut, often called the English or Persian walnut, originated in the mountainous terrain spanning modern-day Iran, Pakistan, and western China. After the last glacial period, roughly 20,000 years ago, the species persisted in small, scattered populations across this belt of Asia. Genetic analysis has shown that what scientists once assumed were natural wild forests were actually shaped by human activity. People were cultivating and trading walnuts far earlier than previously thought.
The Silk Roads played a central role in the walnut’s spread. Traders moving goods between East Asia and the Mediterranean carried walnuts through what researchers call “green corridors,” overcoming mountain ranges and deserts that would have kept the trees isolated. Genetic evidence pinpoints two major waves of human-assisted movement into Europe: an initial mixing of Anatolian walnut stock with natural Balkan populations around 4,000 to 5,600 years ago, followed by a second wave into eastern Europe roughly 1,500 to 2,200 years ago. The name “English walnut” is a bit misleading. English merchants simply happened to be the ones shipping Persian walnuts to the Americas in the 1700s.
What a Walnut Actually Is
Botanically, a walnut isn’t quite a nut in the strict sense. It’s the seed of a stone fruit, similar in structure to a peach or cherry. The walnut tree produces a round fruit with a fleshy green outer husk. As the fruit ripens, that husk dries out and becomes brittle, revealing the hard, wrinkled brown shell underneath. Crack the shell open (usually split into two halves) and you find the kernel, the part you eat, sitting in two lobes separated by a thin membrane. A brown seed coat wraps each kernel and contains a concentrated dose of antioxidants.
English Walnuts vs. Black Walnuts
Two walnut species matter commercially. The English walnut is the one you see in stores. It has a relatively smooth, thin shell you can crack with a standard nutcracker, and a mild, slightly sweet flavor that works in baking and snacking. California produces 99 percent of the nation’s commercial English walnut crop.
Black walnuts are a different animal. Native to eastern North America, they grow abundantly in the Midwest as wild or semi-wild trees. Their shells are thick, rough, and notoriously difficult to open. People sometimes resort to a sledgehammer, and that’s only a slight exaggeration. The shells are so hard they’re actually used as industrial abrasive and polishing material. The flavor inside is intense and earthy, much bolder than English walnuts. Some people love it, but most consumers prefer the milder English variety, which is why black walnuts remain a niche product.
Where Walnuts Are Grown Today
China is the world’s largest walnut producer by a wide margin, accounting for about 59 percent of global output at roughly 1.55 million metric tons per year. The United States comes second at 21 percent, producing around 547,000 metric tons. Chile, the European Union, and Ukraine round out the top five, contributing 6, 5, and 4 percent respectively. The global walnut market was valued at about $9 billion in 2025 and is projected to reach nearly $14 billion by 2031.
Within the United States, walnut production is overwhelmingly a California story. The San Joaquin and Sacramento Valleys provide the ideal combination of hot, dry summers and cool winters that walnut trees need. More than half of California’s walnut acreage sits in just five counties: San Joaquin, Stanislaus, Tulare, Butte, and Sutter. Walnut trees require deep, well-drained soil with a pH between 6 and 7, plus a long winter chill period of 90 to 120 days of cold, moist conditions to properly set fruit the following season. California’s Central Valley delivers all of this reliably.
From Tree to Store Shelf
Commercial walnut harvest in the United States runs from late September through November. The process is heavily mechanized. A tractor-mounted shaker grabs the trunk or major limbs and vibrates the tree until the walnuts fall. Then a blower pushes the fallen nuts into windrows (long lines on the ground), a sweeper gathers them, and a harvester picks them up. This system works best when the orchard floor is smooth and the hulls are still firm and round, so timing matters.
Once collected, the green husk is removed mechanically and the nuts go straight to drying. This step is critical. Walnuts must be dried down to 8 percent moisture content soon after harvest to prevent mold growth and rancidity. At that moisture level, the kernels stay stable in storage for months. After drying, the nuts are sorted by size and quality, then either sold in-shell or cracked and packaged as shelled halves and pieces. Shelled walnuts are best stored in the refrigerator or freezer at home, since their high oil content makes them go rancid faster than most nuts at room temperature.
Why Climate Shapes Walnut Geography
Walnut trees are picky about where they grow. They need at least five to six feet of deep, permeable soil so their extensive root systems can develop properly. Waterlogged or shallow soils stunt growth and invite root disease. The winter chilling requirement is equally non-negotiable: without enough cold hours, the trees won’t flower properly in spring, and yields plummet. This is why walnut orchards cluster in specific regions rather than spreading across any temperate zone. California’s Central Valley, parts of Chile’s central coast, and China’s Yunnan and Xinjiang provinces all share this combination of winter cold, summer heat, and deep alluvial soils. As climate patterns shift, some traditional walnut regions are losing reliable chill hours, which is one reason newer plantings are moving to slightly higher elevations or more northern latitudes within existing production zones.