Did you know that walnuts are not technically nuts? They are actually a seed. And from food to furniture, there ain’t much a walnut tree can’t do.
Origin of Walnuts
The walnut family, which also includes pecans and hickories, stretches back 40 million years. Which is right around the same time canines, monkeys, whales, and elephants emerged. In fact, walnuts are the oldest tree food known to man.
The walnutโs ancestors spent millennia trying out different shapes and sizes before the Persian walnut tree first showed up in the fossil record 3.45 million years ago. From there it spread across large swathes of Eurasia into China, Central Asia, the Near East, and Southern Europe. Recent ice ages caused the walnutโs territorial range to shrink but pockets of survivors persisted after the freezes. This was lucky for early humans, as thereโs archeological evidence that we began eating walnuts 45000 years ago.
Around the World
The first evidence of walnut cultivation goes back 7000 years to the region that is now Iran, during the Neolithic period. The time when humans went from being hunters and gatherers to farmers. Basically prehistoric FarmVille. From there, these delicious nuts radiated out along trade routes to other civilizations in China, the Near East, and Europe.
Greeks & the Persian Walnut
The Greeks and Romans became fond of walnuts after Alexander the Great brought them back from his campaigns in Asia. Greeks had already been farming native walnuts at this time. But one of the new varieties was found to be superior in both size and flavor.
Greeks crossbred this new variety with their own into what they coined the Persian Nut. This variety is now the most popular one worldwide. So thank the Greeks for that! You can also thank Ancient Greece for the alarm clock, your iPhone, bathtubs, having to take geometry, cheesecake, democracy, but hey, also communism and liberalism – wait, are those different? Google Maps, the Olympics and my favorite Olympian — Greg Louganis — but also the pap smear, and vending machines.
Romans & Walnut Trade
After conquering Greece, and some good old fashion cultural appropriation, Rome began farming and trading Persian walnuts across Southern Europe and Northern Africa. Residue of walnuts has been found in the cargo of sunken Roman ships and the ruins of Pompeii. Oh and did ya see the movie Pompeii? Oof. So bad. I was legit rooting for the volcano.
Impact of English Seamen
By the Middle Ages, Europeans began to see walnuts as medicinal, listing the nut in many of their medical books. But, it was English sea-men that helped spread this seed around the world. (sorry, I had to). In-shell walnuts keep for months so they were well suited for lengthy old world trade routes. Thatโs why the Persian and the English walnut variety are one in the same.
And despite making walnuts a global commodity, the English never even grew their own which is very on brand.
California Walnuts
Wild species of edible walnuts do exist in California. But the most cultivated variety, the Persian walnut, they were first grown in California during the 1700s when Franciscan Friars attempting to colonize the Pacific Coast brought them over from Europe. Along with cultural genocide, smallpox, slavery, Catholicism, and syphilis. These โMission Walnutsโ, as the Persian walnuts were called, were grown in the yards of Catholic missions.
If you grew up in California like I did, you probably had to build one of those missions in school. Mine was San Juan Capistrano.
Walnut cultivation became commercial in the 1840s when orchards were planted around San Diego. By the late 1800s, walnut orchards had grown to 15,000 acres across the stateโs southern region. However, Californiaโs second Gold Rush forced walnut cultivation up to the Central Valley, when a farming boom for oranges, lemons, and grapefruits helped make California the nationโs leading producer of fresh citrus. By 1940, the stateโs walnut groves were in the range of 130,000 acres. Today it is over 225,000 acres!
How Walnuts Got Their Name
Our word โwalnutโ comes from the Old Welsh/English โwealhhnutuโ which means โforeign nutโ, as they were brought to Britain from Europe>. Let’s not forget the seamen lol. The scientific name for walnuts is Juglans regia, which is Latin for โJupiterโs Nutโ after the ancient Roman god. The commercial variety of walnut is often called the โPersianโ or โEnglishโ walnut, to differentiate it from other species.
Biological Species
Walnuts dominate a family of trees called the Juglandaceae. This group contains nearly two dozen recognized species of walnuts spread across Eurasia and the Americas. It also includes hickory and pecan trees.
While walnuts are considered a culinary nut, in botanical terms they are actually classed as a seed. Scientifically, a nut is a type of fruit that consists of an inner seed encapsulated by a hard shell that does not naturally open to release the seed. Some examples of botanical nuts are hazelnuts, chestnuts, and acorns. Walnuts first shed their green fibrous outer hull (the exocarp) and then their hard inner shell (the endocarp) after the shell falls to the ground and the seed germinates and grows into a tree, thus disqualifying them as a botanical nut. Harvested walnuts keep their shells until they are removed prior to eating.
Varieties
Of the several regional species of walnut, many are edible. Indeed, North America has several edible species and California has its own native variety. But the main commercial species is Juglans regia or the Persian Walnut.
Within Juglans regia, farmers grow a broad variety of cultivars. In California, the most popular varieties are Chandler, Hartley, Howard, Tulare, Serr, and Vina.
Walnut Nutrition
Botanically, the kernel of a walnut is the energy-rich food source for a growing walnut tree. As such, itโs packed with as much nutrition as can fit into the shell.
Walnuts are made up of 65% fat by weight. These fats are the omega-6 and omega-3 polyunsaturated fatty acids which have been linked to several health benefits. Omega-3 is valuable in particular because mammals cannot produce it themselves so it must be obtained through our diet.
Walnuts also contain antioxidants. These antioxidants include ellagic acid, catechin, phytic acid, and melatonin. Interestingly, some medieval doctors mentioned walnuts as a sleep aid, likely having to do with the presence of the sleep-associated antioxidant melatonin.
Walnuts also contain many important vitamins and minerals, including copper, folic acid, phosphorus, B6, manganese, and vitamin E.
Eating Walnuts
Walnuts are delicious and versatile. Walnuts are nutty and flavorful with a pleasant texture, making them easy to eat plain from the shell. They are commonly added to foods like salads, baked goods, yogurt, stir-fries, or encrusted with bread crumbs on cooked fish. Walnuts can also be ground into a spreadable paste similar to peanut butter. Walnut butter can be added to sauces to provide body, particularly in vegan meals where dairy-based fats need substitutes.
Walnuts are also commonly pressed to make an edible seasoning oil. It can be drizzled on salads or meats as a finishing oil. Walnut oil is also used in cooking to impart flavor, though should be used sparingly as it burns at high temperatures.
Walnuts make appearances in many notable dishes across the world. The Turkish pastry Baklava is one, which features chopped walnuts and honey layered into filo dough. In the 1890s, a famous American hotel, the Waldorf-Astoria in New York City, began serving the โWaldorf Saladโ which is a sweet creamy dish composed of apples, celery, and walnuts.
Global Production
The world produces around 3.5 million tons of walnuts each year. The bulk of that production is in China but the United States, Iran, and Turkey are also significant producers. In the United States, 99% of all walnuts grown come from orchards in California. Most are in the San Joaquin and Sacramento Valleys, but there is some production in the coastal valleys and Sierra foothills.
Farming Walnuts
California is an ideal place to grow walnuts. With that, the aspiring walnut grower should keep the following guidelines in mind.
Soil
Mature walnut trees have deep roots and correspondingly require deep soil. At least 5-6 feet of fertile soil is necessary to support a productive tree. Soil should also be well drained and in an area with a lower water table.
Before planting, the terrain of the orchard needs to be graded flat to ensure even watering. All 5-6 feet of the soil should be loosened to allow the roots of new saplings to take. Raised beds or individual mounds should be formed in which the saplings are planted.
Water
The classic and easiest method of keeping walnut orchards watered is through flood irrigation. Though with Californiaโs current drought conditions, sprinklers or drip lines are now being used more to conserve water. These newer systems deliver benefits on water conservation and reduce runoff. Irrigation lines should be installed prior to planting.
Planting
Grafting is the best practice for California walnuts. Generally, Persian Walnut varieties should be grafted onto a hardy and pest-resistant rootstock like the California Black Walnut.
Commercial Persian walnut trees can be grown from Persian walnuts themselves, but this comes with disadvantages in California. Namely, Persian walnut rootstocks have not developed natural resistance to Californiaโs local pests and environmental conditions. These disadvantages would weaken the tree, making it less productive and commercially risky. Grafting Persian walnut branches onto disease-resistant local Californian Black Walnut rootstocks provides a hardy tree that produces commercially appealing walnuts.ย
Because it can take up to 7 years for a walnut tree to produce commercial grade nuts, so ya donโt wanna f*ck that up.
Weather
Walnut trees thrive in temperate environments but can be damaged by cold. Early frosts can damage branches and late frosts can damage flowers or young nuts. Though frost damage is uncommon in the temperate Central Valley.
During the winter months walnut trees require a long period of cold temperatures for the nuts to be able to set in the summer. These โchill hoursโ are periods of time when the temperature is below 45F. Walnut trees need a somewhat long intermittent period of chill hours lasting 800-1000 hours.
Sun damage and heat can be a threat. Special reflective spray coatings can be applied to reduce the impact of hot weather spells on trees and fruits.
Growing Season
Walnut trees blossoms emerge during the spring in April and May. Walnut trees are self-fertile, so they do not require an insect or bird pollinator. Fruit grows over the summer until maturity in fall. This is when the green hull begins to split. Nuts are harvested from September to November once the hulls begin to split.ย
Walnuts lose their leaves in November and begin to regrow them in April once the frost is over. Over winter, walnut trees experience a process called โdormancyโ which involves losing their leaves and relying on stores of carbohydrates to survive until the spring bloom. This is an important process for walnut trees that ensures they grow healthy nuts.
Harvest
Walnut orchards produce nuts for about 35 years but can remain productive up to 100 years. Harvest begins in September when the green hulls split and the walnuts begin to fall from the trees. The tree is first shaken with a mechanical shaker to drop the nuts. A specialized sweeping machine then gathers the dropped nuts into rows where a harvester can come along to transfer them to a trailer and taken to processing.
The outer hull is removed with a huller and the nuts are then dehydrated where they are then stored until needed for cracking. They are then graded as inshell or shelled walnuts. Inshell walnuts are sized as jumbo, large, medium, or baby according to USDA standards. Shelled walnuts are mechanically cracked, the seed is separated using compressed air, and they are then sized, sorted, hand sorted, and packaged.
And thatโs how walnuts got from Central Asia to California to you.
Sources: UC Davis Walnut Primer 2016, American Heritage Dictionary, Walnuts, UC Davis Fruits & Nuts Info – CA Walnuts, CA Walnuts – Managing Bot Disease, CA Walnuts – Fall & Winter MGMT, Nut Wikipedia Page. USDA Walnut Crop Fact Sheet, Historical Virtues of the Walnut, UC Davis Walnut Produciton in California, Black Walnut Hulls for Dye, Black Walnut Ink workshop, Walnut Blast Media, FAO Data on Walnuts, Walnuts.org, Walnuts UC Davis, USDA Walnut Nutrition Sheet, Healthline Walnuts, Walnut Sustainability, Jay Mahil Farmer Advice, UC Pest Management Crown Gall, Science Daily Article on Walnut Genomics, Loups DโOr Walnut History, Gianni Foundation history of California Agriculture, Permaculture, Walnuts, West Coast Nut article on Walnut Dormancy
