Juglans

( JOO - glanz )

At-A-Glance Information

This genus of trees, commonly called Walnut, needs full sun. Water needs vary by species, and most are low-maintenance trees once established. These trees produce seeds known as Walnuts, which are commonly consumed worldwide. All species are deciduous, and typically reach between 33 and 130 feet tall when mature. They are native to a very wide area that spans from southeastern Europe east through Japan, and from southeastern Canada west and down through the United States all the way 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. 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)
These trees are native to Japan and Sakhalin, reaching up to 66 feet tall when mature. 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.
Juglans californica (California Black Walnut)
This species of Walnut tree is native to California, and has two subspecies:
Juglans californica californica
(Southern California Black Walnut)
This species grows well in zones 18-24, and is native to Southern California. Reaches 15-30 feet tall and just as wide, and tend to be multi-trunked. Nuts produced are rich in flavor. Resistant to Oak Root Fungus. No irrigation needed.
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 just as wide, with a single trunk. ​Nuts produced are rich in flavor. Resistant to Oak Root Fungus. No irrigation needed.

Juglans cinerea (Butternut, White Walnut)
These trees are native to the eastern United States and southeastern Canada. The species reaches about 66 feet tall and is slow-growing. Trees rarely survive past 75 years.

Juglans major (Arizona Walnut, Arizona Black Walnut, Nogal Cimarron)
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.

Juglans mandshurica (Monkey Nuts, Tiger Nut)
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 -25 degrees Fahrenheit.

Juglans microcarpa (Little Walnut, Texas Walnut, Texas Black Walnut, Little Black Walnut)
This species forms a shrub or small tree that reaches about 10-30 feet tall at maturity.

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

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. Varieties that would do well in the Bay Area and surrounding zones include 'Carmelo', 'Chandler', 'Cooke's Giant Sweet', 'Franquette', 'Hartley', 'Payne', 'Pedro', and 'Serr'.

Caring for and pruning juglans Trees

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, 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.

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
  1. 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. If you don't have any potting medium on hand, you can make some. Just mix together equal parts (by volume) moss peat and horticultural-grade sand or grit sand.
  2. 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.
  3. 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. 
  4. 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
  1. 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. If you don't have any potting medium on hand, you can make some. Just mix together equal parts (by volume) moss peat and horticultural-grade sand or grit sand. You will also, after a few weeks, need individual 3-inch pots for each seedling that grows.
  2. 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.
  3. 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.
  4. 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.
  5. 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

Walnut trees suffer from the following pests and diseases:
  • Aphids
  • Walnut Twig Beetle
  • Codling Moth
  • Plum Curculio
  • Ambrosia Beetles
For more information on these pests and diseases, consult the following pages:
​

Gallery

In spring and summertime, these trees provide a nice amount of shade.
Juglans can naturally grow as large scrambling shrubs or trees, depending on their habitat.
Juglans trees have compound foliage.
Juglans trees produce fruits that are green when mature.
Juglans male flowers are very small and bloom on catkins in spring and summer.
Walnut trees are popular landscape shade trees.
These trees are cultivated commercially as a crop, most commonly the species Juglans regia.
Walnut trees are typically leafless from early fall through late springtime.
Juglans fruits will open when mature and release their contents.
Female flowers form at the tips of new growth.
Juglans produce female flowers in spikes of around 7 blooms.
These trees provide great filtered shade for underplantings.
Good underplantings for Walnut trees include Hydrangea and Hosta.
It is possible to grow a handsome understory beneath Walnut trees.
Juglans trees produce a good amount of shade for lawn areas.

Videos

Learn all about these multi-purpose landscape trees.
All about Juglans nigra (Black Walnut).
Learn about these great California natives.
Fifteen facts about Black Walnut trees.
All about Black Walnut trees.
How to harvest and process walnut fruits.

Resources

Juglans - Growing Guide
Juglans microcarpa
Juglans nigra (Black Walnut)
Landscaping and Gardening Around Walnuts and Other Juglone Producing Plants
A Complete Guide to Caring for Juglans Nigra: The Black Walnut Tree
Wikipedia: Juglans
The New Sunset Western Garden Book: The Ultimate Gardening Guide (2012) - Page 385, Juglans; Page 653, Walnut
If you have any questions, comments, concerns, or photos you’d like to add to the gallery, please let me know by sending me a message using the button below!
​