Thursday, 22 January 2015 15:59

How do Walnuts grow?

Walnuts are a stone fruit, botanically known as a drupe, used for the “meat” that surrounds the seed.

  • Latin Name:


    English or Persian walnut:  juglans regia

    Black walnut:  juglans nigra

  • Growth:


    USDA Hardiness Zones 4 - 6  Click here to view USDA Plant Hardiness Zone Map.

    Walnuts are a stone fruit, botanically known as a drupe, used for the “meat” that surrounds the seed. A drupe is an indehiscent fruit, meaning that its hardened endocarp seed is surrounded by a fleshy mesocarp -  the edible “meat” of the walnut. The coffee bean is another example of a drupe fruit.

    The walnut is a large, slow-growing tree with varieties that grow to 100 feet tall. It is a very cold-hardy tree, and requires a cold snap to thrive. The leaves appear in late spring and take anywhere from 4 to 10+ years to begin producing nuts.

    There are two main varieties of walnut tree, the English walnut (sometimes also called Persian or Carpathian walnut) and the Black walnut.

    • The English walnut tree grows up to 40 or 50 feet tall and is hardy to Zone 6. English walnut trees begin producing walnuts within 4 to 10 years of planting.

    • The Black walnut tree is hardy to Zone 4 and grows as tall as 100 feet. It produces highly flavorful walnuts, as well as sought-after wood. However, it  takes more than 10 years for a Black walnut tree to begin producing nuts - which are very hard-shelled and difficult to hull. This is the reason the majority of walnuts grown commercially are of the English walnut variety.

    One characteristic common to all walnut varieties is that the tree produces a chemical in its roots called juglone that inhibits the growth of other nearby plants. it is important to note that walnut trees should not be grown near a garden bed.

  • Propagation:

    Walnut trees may be grown from seed or grafted onto rootstock. Instructions for both processes are in the Grow it Yourself section below.

  • Harvest:

    Walnuts are harvested when they fall to the ground. Most varieties of walnuts reach maturity and drop during the months of September and October.

    The walnut trees are harvested by a mechanical shaker, then a truck follows that collects the nuts off of the ground by means of a brush roller.


  • Storage:

    Walnuts are best stored in an airtight container for one week in the refrigerator or up to one year in the freezer.


  • History:

    Walnuts have a long, rich history dating back as far as 7000 BCE. The scientific name for the walnut, juglans, translates to “Jupiter’s royal acorn” in Latin. The Romans called the walnut “juglans regia” and in Latin, regia means royalty.

    Most historians pinpoint the origin of the walnut tree to Persia. Today, the English walnut is also known as the Persian walnut for this reason. It is theorized the Black walnut originated in the Balkans.

    Walnuts were first traded throughout the Middle East and Asia via the Silk Road. Later, when British merchant marines dominated marine trade routes, the Persian walnut was renamed  the “English” walnut--even though walnuts had never been grown commercially in England.

    Walnuts first arrived in the United States in the late 1700s, in modern-day California,  brought by Franciscan monks establishing missions. The climate in California, similar to the Mediterranean, proved to be an excellent climate for growing walnut trees. The commercial walnut industry did not kick off in California until nearly a century later in the 1870s.

    Today, the United States is among the top three producers of walnuts in the world, with California accounting for approximately 90% of the walnuts grown commercially in this country.


  • Top Producers:

    China, Iran, the United States, Turkey, and Mexico are the world’s top walnut producers (FAOSTAT, 2012).

  • Varieties:

    The two main varieties of walnuts are English/Persian walnuts and black walnuts. Within these varieties, there are many cultivars.

    Popular walnut cultivars include: Ashley, Chandler, Franquette, Gillet, Ivanhoe, Jupanesti, Serr, Tehama, Tulare, and Vina.


  • Products:

    Walnuts are used in a variety of dishes, including salads, desserts, soups and entrees. They can be eaten raw or toasted.

    Walnut trees are also prized for their wood - particularly the Black walnut varieties.


  • Top Health Benefits:

    From reducing stress to decreasing the risk for heart disease, Alzheimer’s and cancer, walnuts provide an large array of nutritional benefits.

    Heart-healthy omega-3 fatty acids are abundant in walnuts, with just one serving (¼ cup, or 30 grams) containing 113% the daily recommended amount. A diet that is rich in omega-3s provides a depression-fighting mood boost, helps with attention deficit disorder (ADHD), aids in the prevention of Alzheimer’s disease and some forms of cancer, and may help to reduce inflammation in diseases such as Crohn’s and rheumatoid arthritis.

    Studies of large amounts of walnut consumption (3 ounces or more per day) indicate that in larger quantities, walnuts may be effective in reducing the risk of breast and prostate cancer. Mice who ate walnuts exhibited decreased tumor incidence and slower tumor growth in a controlled study at the Marshall University School of Medicine in West Virginia.

    Walnuts give a cardiovascular health boost by reducing LDL (bad) cholesterol, increasing omega-3 fatty acids in red blood cells, and lowering the risk of excessive clotting by decreasing platelet activation and maximum aggregation.

    The potassium, magnesium and calcium present in walnuts are minerals that play a role in regulating healthy blood pressure.

    Because people with type II diabetes are often at a higher risk for cardiovascular problems, walnuts may help control blood sugar.

    Walnuts are a healthy weight loss snack. Metabolic syndrome (problems including obesity,  inadequate HDL [good] cholesterol, high blood pressure and excessive blood fats) may be managed in adults who consume one ounce of walnuts daily. Walnut consumption helps to reduce the problems associated with metabolic syndrome without causing weight gain.

    Walnuts are host to a number of anti-inflammatory phytonutrients, omega-3 fatty acids, tannins, phenolic acids and flavonoid that help fight chronic inflammation.


  • Grow it yourself:

    Walnuts are a cold-hardy tree that will not row in warm climates.

    If growing walnuts from seed, it is important to note that walnut tree seeds exhibit embryo dormancy, meaning that the seed will not begin to germinate unless it gets water to it. To start growing, a walnut seed must undergo a process called stratification in which the hard shell is cracked to allow water to access the seed.

    -Purchase walnut seeds from a nursery.

    - To start a seed, crack the walnut’s outer shell and place the walnut in a plastic container surrounded by peat moss or moist sawdust, or start directly outdoors. The temperature should be between 40 and 55 degrees Fahrenheit (start seeds in fall).

    - The seed should sprout in approximately 4 to 5 months. If started in a container, transplant the walnut tree outdoors in an area far from any pre-existing gardens. Walnut trees produce a chemical that is toxic to other plants and inhibits their growth. Keep walnut leaves and shells out of your compost pile for the same reason.

    - When planting multiple trees, they need to be spaced at least 20 feet apart.

    - Grafting a cutting from a healthy walnut tree onto the rootstock of a new tree started from seed is the best way to ensure a fruitful new tree.

    To graft, take a small cutting (8 to 12 inches) that has not budded yet by cutting it away from the tree at a 45 degree angle. Keep the cutting moist. Apply rooting hormone to the graft and cut a section in the rootstock just large enough to slide the cutting into it. Tie with soft cloth and keep moist. The grafted tree should begin to grow on its own in approximately 2 to 3 weeks.

    Walnut trees require little care, but should be watered during periods of heavy drought. If a walnut tree gets too dry, it may produce “burned” walnuts at harvest.

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