Complete Guide to Black Walnut Trees – Juglans Nigra

Pros and Cons of Black Walnut Tree

Pros

An excellent 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

A fully mature Black Walnut tree makes a handsome and stately round crown when grown in the open, free from competition/shading. When allowed to branch fully they are 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. Known as “aristocrat of the fine hardwoods”^[8], the straight closed grain can be used in a variety of applications from furniture, cutting boards, and even smaller art projects.

Cons

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.

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.

Are Black Walnut Trees messy?

Black Walnut Trees are messy. In Autumn the nuts will naturally fall off the tree, and if they are left on the ground the husks will decay into a black gooey substance. The decayed husks will stain sidewalks, concrete, and asphalt. Besides the aforementioned sidewalks and streets – it will stain skin and clothes too!

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 leaflet 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. Also individual leaflets are arranged alternately along the central stem of the compound leaf. Although it isn’t always obvious…so make sure you look closely!

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.^[2][3][4] 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).^[6]

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.^[3]

Root

The root system of Black Walnut Trees consists wide-spread lateral roots and a deep taproot.^[1][6] 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 Tree life span

Black Walnut trees typically mature at 150 years old and have an average lifespan of 250 years. These are very long-lived trees.^[6]

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.^[7]

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.

Sunlight requirements

For sunlight, Black Walnut trees will grow best in full sun, which is at least six hours of direct sunlight per day. They can grow in partial shade, which is four to six hours of sunlight per day, but will not be as tall. ^[2][3][5]

Also note that the amount of sun, and the direction it comes from will heavily influence the shape and branching of a Black Walnut Tree. This has to do with sunlight triggering new branches to form from dormant buds on the trunk. Where ever sunlight shines on a tree, there is a good chance a branch will form.

• A Black Walnut Tree grown out in the open will have much branching with an attractive shape, as sunlight is able to hit it equally from all directions.
• If grown on the edge of the forest, it will have much branching on the side facing away from the forest as this will have the most available light, while the other side of the tree will not have as much branching.
• When grown within mature forest, a Black Walnut Tree will hardly have any branching, and be tall and straight. This is because sunlight is likely only available overhead, so the crown is where all the leaves will be.

Moisture requirements

For moisture requirements, Black Walnuts prefer moist or medium-moist soil that is well-drained.^[6] They do not like wet feet, or locations that are prone to flooding. And a good indicator of a suitable site is one that will support White Oak or Tulip Poplar.^[2][3][4][5]

Even though they are most often found in lower bottom lands, moist woods, and mature forests, the Black Walnut Tree is drought tolerant. This is most likely due to it’s deep taproot, which allows it to tap into water reserves deep underground that other plants cannot reach.

Soil texture requirements

For soil the Black Walnut Tree will grow best in deep soils at least 4′ deep^[5] with a texture range from sandy loam to loam. It can grow in clay-loam, but one must ensure it drains.

Soil pH

Black Walnut trees grow best in slightly acidic to neutral soils. For optimum growth, pH levels should be 6.5-8.0.^[5][6]

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.

Tips for maximizing nut production

If you are growing Black Walnut Trees for nut production there are a few key factors to keep in mind when selecting a site and for maintenance.

• Select sites with loamy soil (learn how to quickly test soil texture here)
• The soil should be moist to medium-moist, but must drain well. (see how to test soil drainage)
• Plant 3-5 Walnut Trees near each other. This promotes cross-pollination, and will increase nut production.^[6]
• Space trees 60′ apart to maximize nut production. This is because when grown in the open a Black Walnut tree can make a wide canopy that can expand up to 60′ diameter. This will allow for maximum nut production.^[5]
• Black Walnut Trees need much nitrogen and potassium for nut production and growth. An old rule of thumb for fertilizing Black Walnut Trees is one pound of 5-10-5 or 1/2 pound of 10-10-10 per year of tree age, spread under the canopy and watered in.^[5][6]

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.^[2][3][9]

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.^[2][3][9]

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. For more background and info on the float test, as well as some summarized scientific studies showing it’s effectiveness, see our write up here.

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.
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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.

As an aside, while I was transplanting some Black Walnut seedlings into larger pots, I was able to get an up-close view of the embryo within the nut. Have a look at this picture – it really shows the anatomy of a Black Walnut that has germinated!

Propagation from cuttings

Black Walnut trees have an extremely low success rate for propagating via cuttings. Hess found that only 2-5% of softwood cuttings would survive.^[10]

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.^[3]

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.^[3]

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.^[3] The condition can prove fatal several years after first noticed.

Diseases effecting Black Walnut

Walnut Anthracnose

Walnut Anthracnose is a recurring fungus that negatively effects Black Walnut trees appearance and nut production. Commonly known as Leaf Blotch, this fungus destroys the leaves of Black Walnut trees. Once it has established itself, it will over-winter in the leaf-litter of fallen leaves.^[5] The first infection will occur in mid-May to mid-June.

When leaflets are infected, they will exhibit many small circular dark brown spots from 1/16th to 1/4″ of an inch. Over the growing season they will merge to form larger dead spots. These infected leaflets will fall from the tree early in July-August.

In particularly bad years, the entire tree can be defoliated and nuts aborted (empty shells or shriveled kernels). Growth is slow in years with severe Anthracnose infection, and trees are prone to winter injury.

Walnut Anthracnose treatment

One can control Walnut Anthracnose via four applications of fungicide spray. The first treatment should be in early Summer when the compound leaves are nearing 12″ in length, and applied in two week intervals until four applications is completed. Note that this is difficult for suburban homeowners with tall, mature trees, and it may be best left to professional arborists.

But if you’ve had the disease already, then you should proactively begin treatment once the compound leaves reach 12″ in length. If you wait until brown spots arrive, then serious damage to the tree has already taken place. As the dead spots on leaves reduce the amount of photosynthesis a tree can perform in a growing season, which harms general growth as well as nut production.

Bunch disease

Bunch disease is a virus that will negatively effect nut production and growth. The main symptom is broom like shoots on branches forming in mid-summer, also known as ‘witches broom’.^[5]

If your tree experiences symptoms of bunch disease, then you should contact a licensed arborist to confirm the diagnosis. Currently, there is no cure for the disease.

Black Walnut Tree symptoms & probable causes

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 fastest growing hardwoods (Red and Pin Oak being the other contenders). 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.

Companion Trees

Some companion trees that grow well near Black Walnut are as follows:

• Black Cherry
• Beech
• Boxelder
• Hackberry
• Hickory
• Red Oak or White Oak
• Sugar Maple
• Tulip Poplar

All of these species can be found growing near Black Walnut trees throughout it’s native range.^[8]

Food

Black Walnuts are edible and a nutritious source of protein.^[1] They are frequently used as an ingredient in baked goods such as muffins and breads, as a topping on ice cream or salads. Ground walnuts can also be used as a breading.

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][11]

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.^[12][13]

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.^[14] 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.

Final thoughts

The Black Walnut tree is an attractive tree with huge benefits for both humans and wildlife alike. It’s stately round appearance looks great on a horizon and can also make brilliant fall color. Although not a popular landscaping choice in residential areas due to the messiness and trip hazards, it definitely has it’s place in our world. In fact just several of these trees could provide a huge amount of protein that one would eat throughout the year, as the walnuts can be stored in cardboard boxes in cool dry places.