Juglans

( JOO - glanz )

At-A-Glance Information

This genus of trees, commonly called Walnut, includes species of large trees that need full sun to thrive in the garden. Water needs vary by species, and most are low-maintenance trees once established. They produce edible seeds that are consumed worldwide. All species are deciduous, and typically reach between 33 and 130 feet tall when mature. They are native to southeastern Europe east through Japan and from southeastern Canada west and down through South America to Argentina. These trees are prized for their attractiveness as well as their wood and edible nuts, and are commonly grown in parks and large gardens.

Juglans Species and Varietals

Juglans is the type genus of the plant family Juglandaceae and includes 21 species. Close relatives of these trees include Pecans and Wingnuts. The best growing zones for Walnut trees vary depending on the species; for more information, see the descriptions below. To find your zone, click here: Zone Map.

Juglans ailantifolia (Japanese Walnut, Oni-Gurumi, Heartnut)
These trees are native to Japan and Sakhalin, reaching up to 66 feet tall when mature. They grow well in USDA hardiness zones 5-9. Bark is light grey, foliage is green, and flowers are insignificant. Nuts mature in mid-fall in the tree's native range. These trees are commonly grown as ornamentals and are perfect for parks and large gardens. The specific epithet ailantifolia refers to the leaf arrangement being very similar to that of Ailanthus altissima, or Tree of Heaven, which it is often mistaken for. This species is considered invasive in Australia, New Zealand, New England and New York (United States).

Juglans californica (California Black Walnut, Southern California Walnut)
This species of Walnut tree is native to California and Oregon, and has two subspecies. Both are resistant to Oak Root Fungus and need no formal irrigation in the landscape in their preferred growing zones, making them perfect low-maintenance, shade-producing edimentals for the garden. Nuts are rich in flavor.

Juglans californica californica
(Southern California Black Walnut)
This species grows well in zones 18-24, and is native to Southern California. To 15-30 feet tall and wide, and tends to be multi-trunked.

Juglans californica hindsii
(Northern California Black Walnut, Claro Walnut)
Native to Northern California and Oregon, these trees grow well in zones 5-9 and 14-20. They reach 30-60 feet tall and wide.

Juglans cinerea (Butternut, White Walnut, Oilnut)
These trees are native to the eastern United States and southeastern Canada. They reach up to around 65 feet tall and are slow-growing. Trees rarely survive past 75 years of age. This species does well in USDA hardiness zones 3-7. Leaves are green and foliage is ferny. Bark is grey-brown.

Juglans major (Arizona Walnut, Arizona Black Walnut, Nogal Cimarrón, Nogal Silvestre, Mexican Walnut, River Walnut, Western Walnut)
These trees love moist soils, and commonly grow in riparian areas and along streams in their native range (southwestern United States and adjacent areas in Mexico). These trees produce small nuts with thick shells, and seeds are oily and edible. Individual trees reach up to 30-50 feet tall at maturity with an equally wide, rounded canopy. Trunks reach up to 2 feet in diameter.

Juglans mandshurica (Monkey Nuts, Tiger Nut, Manchurian Walnut, Chinese Walnut, Onigurumi, White Walnut, Hu Tao Qiu, 胡桃楸)
These trees are native to the Eastern Asiatic Region and reach about 82 feet tall when mature. These are exceptionally hardy trees, able to withstand temperatures down to -45 degrees Fahrenheit. These trees grow well in USDA hardiness zones 3-8. This species is potentially invasive in central Russia.

Juglans microcarpa (Little Walnut, Texas Walnut, Texas Black Walnut, Little Black Walnut, Dwarf Walnut)
This species forms a shrub or small tree that reaches up to between 10 and 30 feet tall at maturity. Foliage is green and ferny. Trees thrive in USDA hardiness zones 5-9, enjoying hot, arid climates.

Juglans nigra (Black Walnut, Eastern Black Walnut, American Walnut)
This species of Walnut does well in USDA hardiness zones 4-9 or Sunset growing zones 1-9 and 14-21 and is native to eastern North America. These trees can reach up to 100 feet tall and 70 feet wide with black-brown, furrowed trunks. These large, hardy shade trees have a long dormant season. They need regular waterings, and produce nuts that are rich in flavor. Can be weedy.

Juglans regia (Persian Walnut, Carpathian Walnut, English Walnut, Madeira Walnut, Common Walnut)
These widely cultivated trees are native to the Caucasus east to the Kashmir region. Bark is smooth and olive-green when new, maturing to silver-grey. Seeds are large, with a rich flavor profile and relatively thin shell. Persian Walnut quickly reaches about between 80 and 120 feet tall when mature. They are best in zones 4-9 and 14-23, and are hardy down to -5 degrees Fahrenheit. Nuts are ready in fall; a single tree can produce up to 150 pounds of nuts. Popular cultivars include 'Carmelo', 'Chandler', 'Cooke's Giant Sweet', 'Franquette', 'Hartley', 'Payne', 'Pedro', and 'Serr'. This species is considered invasive in Central Europe and western North America.

Caring for juglans

Juglans shrubs and trees are best planted in full sun; this exposure will encourage the most profuse flowering and promote lush foliage growth. They can tolerate some light shade, especially during the hottest parts of the day (especially when they are younger), though ideally, they should be receiving about 6 or more hours of direct sun each day to grow vigorously and produce good fruit yields. These trees prefer well-draining soil that is slightly acidic to neutral (with a pH of between 6.0 and 7.5). Walnut trees do not perform well in alkaline soils. They can tolerate a wide variety of substrates, including sandy and loamy soils, but are sensitive to standing water around roots. If soil is heavy clay or very compacted, amend planting site with plenty of sand and organic material before installation. When newly planted, water these trees regularly so that they develop a deep, strong root system. Although these shrubs and trees are considered to be drought-tolerant when established, they do benefit from occasional deep waterings during the warm season. They will produce the best flowers and foliage if given moisture during this time.

Pruning Juglans trees is simple; they take a handsome natural shape with a spreading canopy and only need to be pruned occasionally to maintain a desired shape or size. Young trees should be pruned to create and maintain a strong central leader. The best time to carry out prunings for these trees is in late winter to early springtime, when they can benefit from a light pruning to remove dead, damaged, diseased, or crossing branches. Avoid heavy prunings, especially in summertime, as this can stress the tree out and expose it to disease. These plants benefit from a yearly springtime application of organic compost around their base. If plants seem to be struggling, apply a balanced, slow-release fertilizer in springtime to support the season's growth and flowering. Avoid over-fertilizing, especially with nitrogen-heavy fertilizers, as this will lead to excessive leafy growth at the expense of flowering. These are long-lived trees for the landscape, typically surviving for between 75 and 250 years under ideal growing conditions.

Harvesting Juglans (Walnut)
Juglans trees are harvested around the world for their edible nuts, which are mild and buttery. They are commonly used in cooking and baking, as a plant-based meat substitute, in salads or soups, or soaked and blended to make milk. The species most commonly cultivated as Walnut crop trees are Juglans regia (English or Persian Walnut), Juglans nigra (Black Walnut), and Juglans cinerea (White Walnut). Trees will begin producing small harvests full crops of Walnuts in four to six years from planting and reach full production around age 15. Production will begin dropping off around 30 years. Mature trees in home orchards can produce 50 to 80 pounds of nuts each year, and are prone to alternate bearing, meaning they produce heavy in one year, and a lighter crop in the next. Walnuts are typically harvested between late August and early November.

Edible Walnuts are contained inside of a green outer husk, which will split open when the nut is mature. They will often fall to the ground on their own; it is handy to lay out a tarp or sheet to catch them as they fall naturally for easy collection. Branches can be shaken to release the nuts. Collect them as soon as possible to lower the chance that they will mold, rot, or be eaten by wildlife. Remove the green husks immediately and wash the inner shells. Wear gloves and old clothing while husking, as the husks stain. Spread them in a single layer on a tray or screen in a dry, shady area for between 1 and 2 weeks so the kernel fully dries. They can be stored unshelled for about a year in a cool, dark, dry area. To use them, crack the shell with a hammer to get the nut meat out. Strike at a 90-degree angle to the seam until the nut cracks. Use pliers to easily clip away the shell and retrieve the meat inside. Allow the meat to dry for a day before storing.

Disclaimer: Information contained on this website is strictly and categorically intended as a reference to be used in conjunction with experts in your area. Foraging and consumption of plant parts should never begin without the guidance and approval of a local plant specialist. The providers of this website accept no liability for the use or misuse of information contained in this website.

Propagation

Juglans trees can be propagated either by using cuttings or from seed. To ensure that your propagated plant will have the exact same qualities and characteristics as the parent plant, use the cutting method. If you would like to experiment and see what plant you can grow from seed, just keep in mind that it will not necessarily be the same as the parent plant. To propagate your Walnut tree, follow the instructions below:

Propagating Juglans by Cutting

Gather your materials. You'll need a clean, sanitized, sharp pair of garden shears, rooting hormone, a pencil, and a 3-inch pot filled with well-draining compost or other organic material. A good substrate for propagation of cuttings is a light blend of 1/3 pasteurized soil or compost, 1/3 sand, vermiculite or perlite, and 1/3 coconut coir or peat moss.
In spring or early summertime, choose the plant that you'd like to propagate. Ensure that this plant has had a good watering the night before, as this will improve the chances your cutting will take root. Cut one or more 6 inch portion(s) of the end of a non-blooming branch and strip the leaves off of the lower half. Make a hole in your planting medium by pushing your pencil into the soil. Dip the end of the stem in rooting hormone, and plant it in your pot. Fill in soil around the cutting to support it, but do not pack it down too much.
Moisten with water, and ensure that the pot has good drainage. Your pot should be kept in warm, sunny conditions indoors (and not in direct sunlight). Water whenever your soil is dry under the top layer. After about four to six weeks have passed, your cutting should be rooted. When you notice new growth, you'll know you have roots.
Keep your new plant in an area with bright light (though not direct sunlight) and temperatures between 55 and 70 degrees Fahrenheit. Ensure that the soil stays moist, but not wet, until the next spring, when you can transplant it to its new home. Ensure that the last frost of the year has occurred before doing this, as it can seriously damage your new shrub.

Propagating Juglans by Seed

Keep in mind that the plant you get from seed will not necessarily mimic all of the characteristics of the parent plant. To propagate by seed, you will need a paper bag, a pot or tray filled with well-draining compost or other organic material, a spray bottle and a fork. The best potting medium for seed germination is a light blend of 1/3 pasteurized soil or compost, 1/3 sand, vermiculite or perlite, and 1/3 coconut coir or peat moss.
Harvest your seeds. When flowers are pollinated, Juglans trees produce fruits that are green when ripe. Naturally, these fruits will begin to open up over time and reveal their contents. Typically, this will happen in fall. Collect fruits from the tree or pick them up off of the ground. If there is still some fruit flesh attached to the nuts, remove it and then rinse them.
Walnut seeds need to be cold-stratified before sowing. To do so, place seeds in a plastic bag or other sealable container filled with moistened sand or sphagnum moss. Place the container in the refrigerator, and leave for about three months' time. After this period has passed, remove the container from the refrigerator and lay them out.
Water your prepared seed tray or pot filled with soil, and ensure that good drainage is occurring. Place your seeds in your prepared pot or seed tray about a quarter inch to a half-inch under the soil surface. Cover them with soil and water with your spray bottle. Place your tray of seeds in a warm area that receives bright, indirect light. A greenhouse is the most ideal climate, but a planting tray inside a window will do as well. Germination usually takes 7-14 days from sowing. Once you begin to see seedlings sprout and they are able to be handled, transplant them to their own individual 3-inch pots, filled with the same potting medium as described in Step 1. Loosen the seedlings from the potting medium by digging down with the tines of your fork about an inch and a half, gently working the seedling up until it is out. Then, replant the seedling in its individual pot.
Keep the seedling's potting medium moist, but not wet, by spraying the soil with your spray bottle. Keep your new plant in an area with bright light (though not direct sunlight) and temperatures between 55 and 70 degrees Fahrenheit. Ensure that the soil stays moist, but not wet, until the next spring (after the danger of frost has passed), when you can transplant it to its new home.

Fruits produced by Walnut trees are green, and fall from the tree when ripe.

Walnut seeds are large and brown with somewhat wrinkly exteriors.

Problems and Pests

Certain species are considered invasive in some regions; see the species descriptions above for more information. Check with local authorities before planting. Walnut trees release a natural herbicide called Juglone, which serves to inhibit the growth of plants in their drip zone, limiting competition for water and nutrient resources. The susceptibility of plants to damage from Juglone varies depending on the species. See the chart on this website for more information.

Walnut trees can be susceptible to developing issues with the following pests and diseases in the landscape: