Black Walnut Trees

Facts About the Infamous Black Walnut Tree

By George and Becky Lohmiller
August 19, 2020
black-walnut-trees-roots-evil-ascending-the-giants-wikimedia-commons
Photo by Ascending the Giants: Wikimedia Commons

The black walnut tree (Juglans nigra) is one of North America’s most valuable and beautiful native trees, but it does have a “dark side.”  Here’s what you should know before planting a black walnut in your yard—and how to harvest and eat the tasty walnuts, too!

Facts About the Black Walnut Tree

  • The easily worked, close-grained wood of the black walnut has long been prized by furniture- and cabinetmakers for its attractive color and exceptional durability. Its logs are in such demand for veneer that “walnut rustlers” have made off with trees in the dead of night and even used helicopters in their operations. 

  • The early settlers discovered black walnuts growing in mixed forests from Canada to northern Florida and west to the Great Plains. They found that its rich-brown heartwood was exceptionally resistant to decay and put it to use as fence posts, poles, shingles, and sills.

  • When surrounded by other trees in the forest, black walnuts grow straight and tall with few, if any, lower branches.

  • When planted in the open, the tree will branch out closer to the ground, developing a spreading shape that makes it easier to harvest its sweet, round, two- to three-inch nuts.

  • Settlers snacked on the nutritious walnuts out of hand, added them to soups and stews, and ground them into meal for baking; the hard shells provided a perfect package for storing the nuts over winter.

Black walnut tree

The “Dark Side” of Black Walnuts

Although the black walnut has many uses and benefits, the tree does come with a caveat: the black walnut’s roots, which may extend 50 feet or more from the trunk, exude a natural herbicide known as juglone. This substance is also found in the tree’s leaves and fruit husks.

Juglone does serve a purpose, though. It inhibits many plants’ growth under and around the tree, thereby limiting the tree’s competition, leaving more water and nutrients for itself. 

Tomatoes, potatoes, apples, pears, berries, and some landscape plants such as rhododendrons, azaleas, and lilacs may be killed or stunted if grown in close proximity to black walnut roots or within the tree’s drip line (i.e., under the tree’s canopy). Plan your landscaping accordingly!

A Great Shade Tree

In spite of this, black walnuts make great shade trees for larger properties. They commonly grow to 50 feet or taller and about as wide, but specimens of more than 100 feet have been recorded.

Black walnut’s large, fernlike foliage provides light, airy shade for those grasses and ground covers not affected by juglone. In autumn, the leaves turn bright yellow, contrasting nicely with the tree’s rugged, dark bark.

Black walnuts require a deep, fertile soil with a near-neutral or slightly acidic pH. They are pretty much disease-free and are threatened by few pests.

Picking Up the Nuts

Thud! Thud! Most walnut tree owners have a love/hate relationship because of the fruit which the tree drops in late summer though October. The size of a baseball and colored lime green, the fruit is quite heavy. It makes quite a mess and can be viewed as a nuisance.

Walnut tree owners will spend hours picking up the fruit some years. If you don’t remove the nuts, you’ll trip over them in the dark for the rest of the year (while they rot and mold on your lawn). Hire the kid down the street to pick up those the dropped walnuts (just be careful not to pay per nut—you’ll go broke)! 

black-walnut-shutterstock_182861756_full_width.jpg
Photo Credit: John A. Anderson

Harvesting and Eating Black Walnuts

If you’re willing to do the work of cracking the outer shell, the “meat” inside is edible, as the squirrels will attest; squirrels have little problem chewing through the shells. (Note: Black Walnuts are different than the English Walnuts more commonly sold in stores and shown in the photo above.) 

The sweet, earthy nutmeat inside is well worth the effort. Your grandparents may have harvested the walnuts which can be eaten raw or added to baking (cookies and bars). They can also be toppings on ice cream and cakes, enjoyed as a sweetened candy nut, or ground into meal for a unique flour. 

To harvest, collect the nuts as soon as possible to avoid mold and remove the husks immediately. Wear gloves as the husks stain your hands (and anything they touch). If the nut is too hard, wait a few days and it will brown and soften up.) To remove the husk, you can simply step on them gently with an old pair of shoes. Hose down the nuts in a large bucket to remove any remaining husk.

Dry the walnuts for a couple of weeks on a screen or drying rack or in a hanging mesh bag. You can store them unshelled up to a year. Crack the shell with a hammer to get to the nut meat. (Strike at a 90-degree angle to the seam until the nut cracks). Use pliers to easily clip away the shell to release the nutmeat. Allow the freshly removed nutmeat to dry for a day before storing.

Do you have a black walnut tree? Please share your comments, questions, and advice!

Source: 

This article was originally published in March 2008 and has been updated.

2021_gardening_calendar_christmas_ad.png

Reader Comments

Leave a Comment

Hi, Laurel: Early nut drop

The Editors's picture

Hi, Laurel: Early nut drop can be caused by any number of things, including the tree just trying to limit itself to the optimum amount of fruit. Assuming that disease and soil conditions aren't contributing to this, the most likely cause is often bad or insufficient pollination, one of the main causes of which can be a very wet spring. In your case, spring was rather dry--except for April, which had 2 inches more rain than normal, which is a lot. Let us know if you observe anything else!

I planted 2 English walnuts

I planted 2 English walnuts about 4 years ago they were bare root about 8' tall. they are about 15' tall now but all I ever get is tiny little what looks like walnuts in the spring. but they do not grow any bigger. Are they the walnuts that should get green and drop in Oct.? Thanks Larry

Hi, Larry: The most common

The Editors's picture

Hi, Larry: The most common cause of this is damage from spring cold or frost. If that is not a possibility and the trees otherwise seem healthy, the only thing to do is wait until they mature more. Sometimes an English walnut can take 6 to 8 years before it sort of "gets its feet under it" and begins to produce "normally." Thanks for asking!

We have a very mature (100+

We have a very mature (100+ years) black/english walnut tree. We are in the 4th year of a historic drought and I've noticed that this year, nearing the end of June, the tree has produced very few leaves. Normally it is leafed-out in May. Could this be a result of the drought and do you think there's a chance for recovery when rainfall normalizes? Thanks.

Black Walnut tree not leafing totally in late June.

Black Walnut tree not leafing totally in late June. If it is drought causing it can it recover? What can I do to help?

My neighbor has a large black

My neighbor has a large black walnut tree that is very close the our property line. There are been saplings that have turned into trees on our property line, destroying my fence. I continue to have saplings popping up in my yard, and have to pull them every week. I am very frustrated with this tree but understand my neighbors need for shade in Arizona. How far does the root system go down below ground level? I am considering digging a trench on the property line and putting a metal roofing or similar barrier to prohibit the roots traveling into my side of the yard and saplings appearing. However, I don't want to go through all the trouble and labor of digging it myself if the trees roots go very deep, and the barrier will do no good. If this barrier will do no good, what do you suggest? This tree is driving me crazy! Thank you so much.

It is unclear from your

It is unclear from your question why you would dig a trench. The saplings come from the nuts and this whole "toxic" thing is very mis-leading. The trees grow in harmony with other things in the forest. It is just a very small number of plants that they do not get along with. But to get back to the root quest, yes, as a hardwood, they have quite an extensive root system, it will extend out beyond the drip line.

black walnuts

i dont think they are black walnuts for they dont grow in arizona

We have 3 large black walnut

We have 3 large black walnut trees. This is the first year that they are dropping the newly forming nuts in the spring. We are a little concerned as to why this is happening. Can you help?

Hi, 3D: This could be from

The Editors's picture

Hi, 3D: This could be from any number of things, including some sort of infestation. Another thing that happens is that unkind weather conditions interfere with spring pollination, so the weakened tree starts dropping nuts. About all you can do is observe carefully as time goes on and see if anything seems to be afflicting the tree. Otherwise, hopefully it should be stronger next year.

Two years ago I had an old

Two years ago I had an old black walnut cut down and the stump ground up. I now would like to plant veggies there. Do I need to remove all the chips or can I mix in soil and plant that area. The mound of chips has shrunk by 3/4 over the past 2 years. Is it still toxic?

Hi,somewhere I read that you

Hi,somewhere I read that you can use black walnut for fence posts. Questions: does the toxicity apply to fence posts and if you cut down the tree, how do you destroy the toxicity?
Thank you.
Jay

Nice blog!yes black walnut is

Nice blog!yes black walnut is beautiful and herbal medicine tree.Dried Walnut Hull or its extract helps in relieving asthma, cough, and chronic bronchitis. Regular consumption of this herbal extract offers excellent relief for people of age suffering from chronic respiratory diseases. In Asian countries the use of black walnut and its extract a popular home remedy for treating respiratory diseases. Check out the Benefits of Black Walnut here: buytincture which is best herbal store.

We just purchased some land

We just purchased some land that is covered in black walnut trees. We will be taking some down to plant grass and do landscaping. How long are the roots toxic after they ate cut down?

Thanks!

Hi, Susan: The duration of

The Editors's picture

Hi, Susan: The duration of the toxicity of juglone, the poisonous agent of black walnut trees, really depends in some part on the type, density, and drainage of the soil (although juglone is not very soluble). Still, it can last for 5 or 6 years or even longer -- and it can be much shorter, too. There are two things to do: (1) When you "stump" (pull up the stumps on) your land, try to get as much of the big roots as possible, even if it means a little more work. They have a massive root system, but every little bit that's not there helps. (2) Research online or at your library what plants are tolerant of juglone -- there are quite a few: Kentucky blue grass, for example. Good luck!

I have a few acres of black

I have a few acres of black walnut trees. Unfortunately they were planted about 10 feet apart so they have grown tall and thin. They are about 50 feet tall with trunk diameters of 6-12inches. I'd like to thin some areas in hopes that the trees will branch out and spread at the crown. Is it too late for them or will opening the area encourage them to branch out?

Thanks!

Hi, Corinna: This is a good

The Editors's picture

Hi, Corinna: This is a good question, with answers so complicated that we dare not go there. Some of this depends on the purpose of the trees (harvest anything? shade? beauty?). In any event, walnut trees with this extremely tight spacing are best thinned when their diameters are 3 to 4 inches, not 6 and up. Your local climate and soil conditions might come into play, too, not to mention the extensive root systems. We recommend consulting with a professional arborist. Good luck!

Poison ivy vines are growing

Poison ivy vines are growing exclusively on all my walnut trees in the unkept, mature woods of the older home I just bought in northern MD. Wild grape, oak, and rosa flora vines are grwing on all the other trees but never on the walnuts. Why? I love and hate it. How agressive can I get with herbicides and not hurt the trees?

Hi, Mary: This seems to be a

The Editors's picture

Hi, Mary: This seems to be a question not only of arboriculture, but also of semantics. Why poison ivy is not growing on your other trees, we don't know. Why the grape, etc., are not growing on your black walnuts is because b-w's produce an herbicidal substance called juglone (see our intro above) that is toxic to many plants. It is not toxic to poison ivy, which is why p-i will grow on black walnuts. In and of itself, a good (p-i specific, if possible), organic herbicide is not going to kill the trees. In and of itself, it is also not going to kill the p-i vines. The thing to do is first to thoroughly cover every inch, nook, and cranny of yourself with protection from p-i's urushiol oil. Let us repeat that: Cover yourself totally. Then carefully remove (cut out) sections (a foot long is good) of the vines, which will kill what is above (but the oil will still be potent for a year or two). Then, focus on spraying what is below the cut. Carefully discard the cut sections in a way that no one can touch them or what they have touched. By the way, though: Poison ivy leaves are edible by quite a range of wildlife. It's a complicated situation, and no doubt this reply has just scratched the surface.

I just recently found out I

I just recently found out I have a black walnut tree in my next door neighbors home right on my fence line. It drops these green balls onto my roof and scares the crap out of me lolz...I grabbed one today threw it on my cement patio it broke the green ball and I seen it was a walnut shell on the inside. Now I live in northern illinois and my neighbors never planted the tree. How the heck is it surviving?

Normally, you need a special

The Editors's picture

Normally, you need a special tool to crack a black walnut shell (that is stronger than a common nut cracker) but I guess you found a creative solution! :-) Inside is a sweet nut that you can eat or make into pies.  The tree may have seeded itself; it's hard for us to know. Just keep in mind that the area near the tree can be toxic to other plants and vegetables, so something to keep in mind when you consider whether you want to keep it.

I have a whole yard full of

I have a whole yard full of black walnut trees and a garden right next to one and my plants don't get toxic as a matter of fact I had more tomatoes than I knew what to do with.

We have a Black walnut tree

We have a Black walnut tree in our front yard in Lincolnton, N.C. My question is we have been living here 5 years, and this is the first year it is not bearing nuts. Do they have a non-bearing year like the Pecan tree. Thank you

Some black walnut cultivars

The Editors's picture

Some black walnut cultivars are indeed prone to alternate bearing or just bearing more heavily every other year.
If your leaves seem unhealthy, here is also a fungus that can effect nut production but can be controlled by fungicide applications. You could contact your cooperative extension for further diagnosis.

My question is when you first

My question is when you first plant your black walnut tree and its only a foot tall,will the deer bite the tops off of them and kill the tree ?

Yes, deer will eat them, I

Yes, deer will eat them, I think it is candy for deer. lol I keep mine fenced until they are about 4-5' tall and the you still need to protect the trunk from deer rubs.

I have or I think I have

I have or I think I have black wallnut trees on my prop. about 35 feet apart. For 15 years I,ve lost many pine trees that I've planted around these black wallnut trees. Is there a pine tree that resists the JUGLONE that was talked about?

I take exception to your

I take exception to your comment regarding Black Walnut pest.
You mention few are out there, we have 17 walnut trees in our back yard.
We live in S.W. Ohio 2.7 miles from a large Veneering company. They are suspect of importing diseased walnut trees from Colorado. We have a major infestation of Walnut Twig Beetles (size of a sesame seed) which carry a fungus which causes 1000 Canker Disease.
Our situation is so bad the state of Ohio Agriculture Dept. has conducted training classes in our yard. We've had Professors from Ohio State University and University of Tennessee investigating and taking samples. Plus the Ohio Division of Forestry Department had 25 of their personal here for observation.
We currently have one of in excess 110 traps around the county. These traps are not to catch the beetles for disposal rather they are for verification of the infestation in other areas.
It's now up to us to take down these dead or dying trees. Then we must figure out a means of disposal without removing any portion including saw dust from the county of which we live Butler County Ohio.
I decided to pass this information on in the event your Walnut trees decided to start dropping leaves early and often all summer long including.

Thanks for your comment. This

The Editors's picture

Thanks for your comment. This column was written in late 2005 or early 2006 and we appreciate your update.
The walnut twig beetle is a pest that seems to be increasing among black walnut trees (primarily affects black walnut Juglans nigra). Tinier than a grain of rice these beetles carry the fungus Geosmitha morbida that eventually (within a couple or few years) infects the tree and starves it to death. See: http://www.aces.edu/ucf/Blackw...
Disposal of the remains can be a complicated and costly procedure.

Do you need to fertilize the

Do you need to fertilize the soil and also what pesticide do you need to treat the black walnut trees? Thanks

Pages