Complete Guide to Black Walnut Trees – Juglans Nigra

Updated January 15th, 2022

The Black Walnut Tree is a large deciduous tree native to Eastern North America that produces edible nuts in the fall. Growing to heights of 120′ (40 m) by 50′ wide (~15 m) in optimum conditions, the Black Walnut can make an excellent shade tree. The main drawback for the Black Walnut is a chemical its roots produce and secrete called Juglone, which kills many different species of plants should their root come into contact with it.

So, one must be aware of that fact, and chose companion plants accordingly.

In this article:

• Black Walnut Tree Facts / Quick Reference
• What are the pros and cons of Black Walnut Trees?
• Identification / Characteristics
• Black Walnut Toxicity
• How to Grow and Care for Black Walnut trees
  • How to Germinate Black Walnuts
• What Wildlife, Pests, and Diseases effect Black Walnut trees?
• Where to buy Black Walnut Trees
• Uses of Black Walnut Trees

Facts

• It is hardy from USDA zones 4-10. Check your USDA zone here.
• Growth Rate – Black Walnut Trees grow between 12-30 inches per year (30-70 cm), depending on conditions
• Can start producing nuts as early as 5 years old, with significant production once it reaches 10 years old
• Nuts attract a wide variety of wildlife (squirrels, chipmunks, etc)
• A true favorite of woodworkers (and the author), the dark closed-grain heartwood has a beautiful dark brown color
• The scientific name of Black Walnut is Juglans nigra [2]
• All parts of the tree, but particularly the roots produce Juglone, which can prevent growth or kill certain plants growing under or near them
  • Want to see full list of plants that should not be grown under Black Walnut Trees? Click HERE
• Shavings from Black Walnut should not be used as horse bedding, as it is toxic to horses

Black Walnut Tree Native Range

The native range of the Black Walnut Tree is North America, primarily East of the Rocky Mountains. Although it has become naturalized in some Western states such as Utah, California, and the Pacific Northwest. [1]

Black Walnut Tree Reference Table

Common Name	Black Walnut
Scientific name	Juglans Nigra
Bloom Time	Late Spring
Bloom Duration	2 weeks
Color	Green/yellow
Bloom Size	Small florets, 1/8” wide (3 mm)
Flower Characteristics	Florets will be hang down, arrayed on a stem. Female florets are several to a group and the same size as male.
Height	80-130’ (24-40 m)
Spacing/Spread	12’ (4 m) (for nut production) 25′ (8 m) for general landscaping
Light Requirements	Full sun – Full Shade
Soil Types	Clay, Loam
Moisture	Moist to Medium
Maintenance	Pick up the walnuts each year! Or let the squirrels do it
Typical Use	Woodlands, border, planting for nut production, timber
Fauna Associations	~ 40 species of moths and insects feed on Black Walnut. Squirrels, chipmunks, eat nuts.
Larval Host	Over 20 different moths
Sowing Depth	1”
Stratification	Plant in fall, direct sown
Native Range	USDA Zones 4-9

Pros and Cons of Black Walnut Tree

Pros

Shade Tree

Black Walnuts grow quickly and can reach towering heights. This makes them a potential shade tree for any home. Just make sure you space them away from the house accordingly to avoid walnuts clogging your gutters.

Beauty

The general shapeliness of a Black Walnut tree make them very attractive when grown in the open, free from competition/shading. When allowed to branch fully they can be a very attractive tree.

Food

Black Walnut trees will produce large crops of edible nuts for free. There are different manners of processing or removing the husks. But Black Walnuts are nutritious and can be used in a variety of foods, or eaten by themselves.

Hardwood

The lumber that can be produced from Black Walnut is absolutely beautiful. The straight closed grain can be used in a variety of applications from furniture, cutting boards, and even smaller art projects.

Cons

Fall Cleanup

Mature Black Walnut trees will produce nuts each year, but roughly every 5th year they will have a bumper crop. This can lead to tons of small golf-ball sized green balls littering streets, sidewalks and yards. Although the squirrels and chipmunks will bury most of them, working around them can be annoying until they are buried.

Juglone Poisoning

The roots, bark, and leaves of Black Walnut trees produces a chemical known as Juglone that is toxic to many plants. Furthermore it can be an irritant to your skin if you are susceptible.

Black Walnut Identification, Physical Description, and Characteristics

Black Walnut Trees grow tall! Over 100′ for a mature tree, and they can branch to 50′ diameter. The rough bark can be mistaken for Ash or Tulip Poplar trees, with its rough vertical ridges. But the leaves are more unique, being ‘compound’.

A true confirmation of a Black Walnut Tree can always be done in the Fall (September/October), by looking for the many 2-4″ diameter nuts that will be in the tree, and all over the ground. And should you see the cross section of the log, you will have no problem identifying it by the dark-brown heartwood surrounded by white/yellow sapwood.

Trunk/Bark

Typically the trunk will be quite long and not have branches, making it excellent for lumber. Black Walnut bark consists of rough ridges that run vertical. Significant branching can/does occur in the upper 2/3 of the tree. At full maturity, the trunk of the Black Walnut can be up to 6′ diameter (2 m).

The limbs will have more immature bark, which will be much smoother. You often see the limbs having bark that is smoother than the mother trunk in various species, such as Redbud or Shagbark Hickory.

Leaves

The leaf of the Black Walnut Tree are compound, with alternate leaves. The total compound size is around 18″ (30-60 cm) long, give or take 6″, and approximately 6″ wide (15 cm).

The size of the individual leaf is approximately 1″ (25 mm) wide by 3″ (~75 mm) long. The leaves on the tip of the compound are shaped differently than the others, being smaller or misshapen. Individual leaves are shaped like a spear-tip, and have serrated edges like a saw.

Black Walnut leaves turn yellow in Fall when temperatures begin to drop. Also, it is one of the first trees to have its leaves change color in Autumn. So, when you see Black Walnut leaves turning yellow, you know cooler temperatures will follow soon!

Flower

In Spring Black Walnut Trees will produce small florets and bloom. Since Black Walnut trees are monoecious, it will have both male/female flowers and will self-pollinate. The male flowers are attached to stems that hang down cylindrically, and are about 5″ long (12 cm). Female florets are in small groups on a small spike, and will have 3-6 florets. The size of both male and female florets are about 1/8″ (3 mm).

The female florets will eventually turn into large, golf ball sized nuts. These nuts will have an outer green husk that eventually turns yellow to black. A mature nut will be the size of a ping-pong ball, with a black/shriveled and rough texture.

How long until a Black Walnut Tree produces walnuts?

For Black Walnut trees grown out in the open, or in landscaping application, seeds may start being produced at 4-6 years of age. When it comes to trees grown within the forest it may take 20-30 years until nuts are produced. [1]

Root

The root system of Black Walnut Trees consists wide-spread lateral roots and a deep taproot. The root produces a chemical called Juglone, that inhibits or prevents growth of certain plants. This mechanism helps reduce competition, raising the chances of the individual tree to survive and collect nutrients.

Black Walnut Trees poisoning other plants

Black walnut trees produce a chemical in their roots called Juglone that will poison and kill other plants and trees. Juglone is chemically known as C₁₀H₆O₃ or 5 hydroxy-1, 4- napthoquinone. This chemical will slowly stress and kill susceptible plants. [2]

I’ve done some exhaustive research compiling all known plants that are susceptible to Juglone poisoning. Head over here to get the full list of known plants that will die from Juglone ==>HERE

What plants grow well near Black Walnut Trees?

We have also researched and compiled a complete listing of plants known to grow well near Black Walnut Trees. These plants are impervious to Juglone. Our information is based Scientific Journals, University Studies, and Ag Extension resources.

You can read our full list of 201 Plants that are tolerant of Black Walnut Trees ==> HERE

Grow and Care of Black Walnut Trees

This tree likes moist soil that is moist. It will grow in a variety of conditions and almost any soil, from sandy to clay – the main thing is that it needs moist, well-draining soil to thrive. It can tolerate occasional flooding, as evidenced by its propensity to grow near streams, creeks, ponds. If you provide it the necessary space, moisture and good soil, then you can expect significant year over year growth.

How to care for

Not much care is required. Just provide this tree with conditions that it prefers, and you will have a thriving tree to be enjoyed by future generations.

Maintenance

The biggest maintenance job for this tree is cleaning up the nuts. If you plant this near a sidewalk or street, it will be littered with the nuts. When crushed, there is a black husk that stains skin, clothes, and pavement. It is difficult to remove the color. Eventually the squirrels will likely get all the nuts and bury them, but not before they start to break down naturally and stain areas.

While the Black Walnut tree can provide excellent shade, food for you and wildlife, and is beautiful, the walnuts falling to the ground can be a bit messy in some applications. If you would like a tree that looks great, provides nice shade, grows fast, and supports wildlife then I suggest you look at the Pin Oak Tree.

How to Propagate Black Walnut Trees from seed

Black Walnut trees can be propagated from collected nuts. After the walnuts naturally start falling from the tree, you should collect some from the tree itself, not the ground. Then, remove the husk and test the black walnuts viability by seeing if it sinks in water. Plant viable Black Walnuts 1-2″ deep. Trees will sprout in the Spring.

If you collect some black walnuts and wish to grow them from seed, you first need to do a test to make sure the nut is a viable seed. Also, Black Walnuts need to undergo cold moist stratification or be winter-sown to germinate.

Testing Black Walnut seed viability

Checking viability of the walnut itself is quite easy.

1. Put on rubber gloves and get a sharp knife. I use a hunting knife, but a chef’s knife would work well too.
2. Cut around the husk, then twist the knife to pop-off and remove the husk. This can be a dirty job, so the gloves are important. The husk of Black Walnuts can stain almost anything.
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3. Rinse the nut a few times to clean.
4. Drop the nut into water and let it sit for 60 seconds. If a walnut sinks, then it is viable. If the walnut floats, discard it.

After husking and discarding nonviable Black Walnuts, you should plant them or stratify them. One thing to note, squirrels, chipmunks, and other rodents will dig up walnuts to eat. So you need to have a way to protect them. If you are not prepared for that yet, then consider storing them in the fridge by cold-moist stratifying them until you are ready to winter-sow the seed.

Cold Stratify / Storing Walnuts for germination

To cold stratify and store Black Walnuts prior to planting, get a large 1-gallon zip-lock bag and some sand or vermiculite. Mix the sand/vermiculite with water so that it is damp. The amount of dampness is that if you squeeze a handful only a couple of drops should drip from your hand.

Then, place your Black Walnuts into the center of the mixture, and place into the zip-lock bag. Store this in the fridge until you are ready to plant.

How to plant and germinate Black Walnuts

Since Black Walnuts need a cold treatment, winter-sowing is the easiest method. Just let mother nature do the work for you.

1. Fill a container with moist potting soil.
2. Planting Depth – Plant Black Walnuts 1-2″ deep into the soil (2.5-5 cm)
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3. Set the container outside in a location that receives morning sun and afternoon shade
4. Protect the container from squirrels and rodents. Hardware cloth, screens, or something similar with a rock on top works great.
   • 
5. Germination will occur in roughly the middle of Spring, once temperatures begin warming up overnight

Video guide to growing Black Walnut Trees from seed:

Below is a short video on how to grow a Black Walnut tree from Seed. This video contains all information you need to successfully germinate the nuts.

Wildlife, Pests, and Diseases

Fauna Associations of Black Walnut Tree

More than 20 different species of moth larvae feed on black walnut trees, making it a valuable part of the ecosystem. Additionally, there are another 20 or so insects whose larva bore into the bark to feed. [1]

Chipmunks and squirrels will collect and bury nearly all the nuts, to use as food throughout the winter. In that regard they are valuable for our ecosystem. Also, by way of burying them they help propagate the species. [1]

Pests

A condition known as ‘Thousand Canker Disease’ effects mature Black Walnut Trees. A predatory beetle walnut twig beetle (Pityophthorus juglandis) eats on the tree, providing a vector for a fungus to lead to cankers on the tree. The condition can prove fatal several years after first noticed.

Disease

General fungal issues also effect foliage of Black Walnut trees. Both white mold and bull’s-eye leaf spot can negatively effect the trees appearance and health.

Uses for Black Walnut Trees

Landscape Use

Black Walnut trees make excellent shade trees. Their ability to grow up to 30″ per year make them one of the faster growing hardwoods. The main drawback to Black Walnut trees in a yard or sidewalk is the nuts that will fall, that can be a tripping hazard and make a mess.

Food

Black Walnuts are edible and nutritious tree nuts that are grown and prized for food. [1] Black Walnuts are often used in baking, as a topping on ice cream, or salads. Ground walnuts can also be used as a breading. Although one must harvest them prior to squirrels and chipmunks that quickly bury and cache the nuts.

Nuts can be de-husked and dried for storage. Cracked nuts can be frozen and preserved for up to two years, making Black Walnuts a valuable food that can be stored long-term. Homesteaders in particular should take note of this valuable protein source.

Lumber

Black Walnut lumber is one of the most prized and valuable hardwoods native to North America. The ability of the tree to reach large trunk diameter and height make large boards possible, and lots of them available within a single specimen. The lumber is used commonly as veneer, gunstocks, and furniture. [1][4]

Lumber from Black Walnut Trees that grow in yards

If you are reading this and have a few tall Black Walnut trees in your yard, you may be thinking you are sitting on a small fortune. While it is possible you could have trees with valuable trunks, sadly it is unlikely that you could get more than a few hundred dollars for your trees.

Yard trees often grown in the open will have many knots and branching that diminish the value greatly. Furthermore, most professional loggers will not haul equipment to a residence for a single tree, as the overhead costs are too high. In general, you need 10-20 acres of hardwood forest at a minimum for a professional logger to come harvest timber. [3][5]

That being said yard trees are not without lumber value. Depending on the market one may attract a small hobbyist with a portable sawmill to come for general lumber or the recent trend of making live-edge or slap boards.

Recently a 250 year old Black Walnut Tree was illegally cut down for lumber. A man mistakenly thought the giant 72″ trunk diameter tree was his. Ultimately, he was paid ~$2,000 for the tree, and the loggers sold the tree for over $10,000.

General woodworking with Black Walnut

Black Walnut wood is so beautiful that anyone with a basic skill of hand tools can create works of art. Yours truly has rescued pieces of firewood to create small Christmas gifts such as the business card holder below. And even split logs lengthwise to make rustic benches.

The closed grain wood of Black Walnut wood makes it a great choice for cutting boards, mallets, and bowls/spoons.

Related ==> Learn how to make your own mallet from a log HERE!

Medicinal

There are over 70 uses for Black Walnut Trees documented by 16 different tribes. [6] Most common uses is eating the nuts for food, or using the bark/husks as a dye.

Bark was used by the Cherokee “cautiously” as it was toxic. Often as a dermatological aid, toothache, an infusion for smallpox, and as a dye. The nuts were eaten and wood used for furniture and carving.

Many other tribes utilized the bark in decoction, infusions, or rubbed on skin to treat various ailments. Symptoms such as carhartic, ringworm, inflammation, intestinal, or emetic issues were all treated in some manner with the bark.

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