Black Walnut Trees

Facts About the Infamous Black Walnut Tree

By George and Becky Lohmiller
August 19, 2020
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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)! 

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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.

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Reader Comments

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Fail to leaf after spring frost

The Editors's picture

This one is beyond our ken, E, but we found some information that may shed some light on your tree’s failure to leaf. (Sit down; there’s a lot to read.)

This page, from the Oregon State cooperative extension service addresses frost situations and more: http://horticulture.oregonstate.edu/system/files/u1473/em8907.pdf

Purdue says plainly: “Black walnut is very susceptible to light freezes…” See here: https://www.extension.purdue.edu/extmedia/FNR/FNR-119.html

You can, and should, consult your local cooperative extension service for local advice. See here and choose your state: https://www.almanac.com/content/cooperative-extension-services

Walnuts planted in 1972

Planted 100 seedlings in 1972, then another 3,500 in 1987, of which over 1,000 (drought year in 1988) are still alive and now growing well. This article says the seeds are sweet and two to three inches. Black walnuts have a strong, bordering on bitter, flavor, and in my experience average about an inch in diameter. Some say that they are a slow growing tree. I've got some second-generation volunteers now approaching 50 feet in height, had to remove one second generation tree last year that measured over 20 diameter at the base, about 40 feet through the crown. The hard shell may well protect the nuts for storage, but they must be protected from mice that will chew right through the shell, even chewing through the walls of a plastic container to get to them. Nuts planted in the fall will often sprout the following year, as the shell opens along the seam. Squirrels will "discover" the new seedlings and pull them to get at the nut, although they are also responsible for burrying more nuts than I've ever planted.

Black Walnut tree leaves

Composting: Can you compost the leaves? There was a study that OSU did. That they were safe to compost. They lose the juglone over time of composting.
The one thing is can you put that compost around tomato plants?

black walnut compost

The Editors's picture

As you mention, juglone is the substance in black walnut trees that can cause severe damage and even kill solanaceous crops (tomatoes, potatoes, peppers and eggplant). However, not all plants are susceptive to the chemical. Edibles that are tolerant of juglone include corn, beans, onions, beets and carrots.

Other trees that carry juglone include butternut, hickories, and pecan; black walnut has the highest concentration of it.

Walnut leaves can be composted because the juglone toxin breaks down when exposed to air, water and bacteria. The toxic effect can be degraded in two to four weeks. In the soil, breakdown may take up to two months after the living walnut tree has been removed. Mulch or woodchips from black walnut are not recommended for plants sensitive to juglone. However, composting the woodchips for a minimum of six months allows the chemical to break down to a safe level even for plants sensitive to juglone.

Black walnut's outer shell

This article, the comments and your well-stated answers were a joy to read. My question is why does the hard green outer shell have such a pungent citrus smell?

Something to Ponder....

I have a larger mature black walnut tree in my garden. I have had wonderful luck with Hostas and most spring bulbs. I have tulips, daffodils, iris and hyacinths. There are several guides for tolerant plants.

Then I tried putting in a KOI POND.....Walnut trees kill fish. Does anyone know if they are safe for frogs????

Black Walnut Tree Toxicity

The Editors's picture

Hi Michelle,

We’re sorry to hear about your koi pond! It’s hard to say for sure if the black walnut tree toxins will affect frogs: It is poisonous to dogs and horses, but not to cats. The area of affected soil is usually 50 to 60 feet surround the tree, depending on its age. 

increase in the amount of spring unisex flowering??

this year we have an extreme amount of the green flowering type of powder like strings falling from the trees. Does the increase of this make an increase in the the likely amount of nuts they will produce?

hydranga

Need to know if they will grow by Black walnut trees !!???

The Short Answer

The Editors's picture

Hi, Marie: Need to tell you nope, not well. Thanks for asking!

We were told by a tree

We were told by a tree trimmer that black walnut trees are subject to emerald ash disease, and that we should get something like ash borer treatment (not sure that is the correct wording) for it. Is this true?

black walnut and emerald ash borer

The Editors's picture

Emerald ash borer is apparently a threat to black walnut and other trees in much of the country. We are not qualified to comment on treatment; we advise that you consult with an arborist. Your local cooperative extension service may be able to help you identify one; find your state and click here for coop extensions: http://www.almanac.com/content/cooperative-extension-services

FWIW, this page identifies numerous treatments for the EAB, as it is often called: http://hort.uwex.edu/articles/homeowner-guide-emerald-ash-borer-insectic...

We do not and cannot recommend or otherwise give any judgment on the products mentioned on that page; we provide it only for your general information.

We hope this helps!

 

Black walnut trees EVERYWHERE!

I have more than a dozen black walnut trees in my yard. I would love to have a veggie garden or plant some rose bushes or fruit trees. I am open to any plants that will grow. I live in zone 7(a). What will grow in my yard with these trees surrounding me!?

black shadow

The Editors's picture

Wow, that’s a great question, but it is not one that we are prepared to answer. We do not know what your options are, but we can recommend that you contact your local coop extension service (usually part of a college or university) or a local nursery. You could have a specialist come to see your site, but that might incur expense. No matter what course you take next, it is not going to be easy making choices or decisions. Give yourself time…do it once, the way you really want it.

@Venus

I moved into an old farm house w a couple black walnuts on the property. I haven't tried to grow anything near my trees. But, there were already established black mulberry and honeysuckle tree/bushes in the same area. The mulberry and walnut touch branches. They are around a car length apart. I have harvested the nuts for baking and made wood stain from the hulls.

I built 2 raised vegetable

I built 2 raised vegetable garden beds (filled with a mixture of compost, sand and peat moss) near my mature black walnut tree and have had no issues with anything struggling to grow. It's not close enough to be under any of the branches (obviously shade isn't great for growing vegetables anyway) so I would imagine a vegetable garden would be fine as long as you're growing the vegetables in "fresh" soil and not soil shared by the walnut tree roots.

Natural growth of walnut tree

Hi. I am wondering if left on the ground will a walnut, even with the husk on, eventually take root if all the conditions are optimum? Would the rotting husk give way to a shoot coming through the hard shell? How does it work? How long would it roughly take from new nut on ground to seedling or sapling stage? Thank you!

Walnuts

The Editors's picture

It is possible but not probable and it would take a very long time–possibly years for the shell to break down atop the soil (and the likelihood of the nut staying put for that long is slim); burying it speeds up the process due to moisture and microbial activity in the soil. Taking off the husk further speeds the process.

@Guidroz

I've heard that planting the whole husk will help break down the walnut for germination. Not sure if this is accurate and have never tried it. I would consider attempting both to see if there is a noticeable difference.

Yes. Seeds in the ground will

Yes. Seeds in the ground will just sprout and grow. We have dozens of black walnut trees on our property. My yard is basically a walnut nursery. I have hundreds of them all over the place. The previous owners just let the nuts fall. I'm sure many of them have been mowed down year after year. Either way, yeah, stick them in the ground and they will grow! It probably does take a few years to cold stratefy and break through the shell.

Yes. Seeds in the ground will

Yes. Seeds in the ground will just sprout and grow. We have dozens of black walnut trees on our property. My yard is basically a walnut nursery. I have hundreds of them all over the place. The previous owners just let the nuts fall. I'm sure many of them have been mowed down year after year. Either way, yeah, stick them in the ground and they will grow! It probably does take a few years to cold stratefy and break through the shell.

Planting near black walnut tree

What if any plants can grow well near black walnut trees. I have a very large side-yard that I would love to fill, but am not sure what will live near this tree. I have already lost many plants and trees due to not knowing about this problem before. Any information or advice would be very welcomed!

Compatible plants

The Editors's picture

There are many plants that tolerate the toxicity of black walnut. Perhaps you could help to narrow down our list by telling us if you are looking for trees, shrubs, perennials, or annuals. Happy to assist once we know what you’d like to plant.

 

I noticed the soft outer

I noticed the soft outer shell of Black Walnuts degrade fairly quickly so I heaped tons of the nuts on my compost pile. Are they toxic to my compost?

Numerous Black Walnuts this year

Hi,
We have lived in this house in Kansas, west of Kansas City, on 10 acres for almost 20 years and we have never seen this many walnuts. I picked up over 100 lbs from one tree without even trying. The limbs are breaking off because of the weight of all the walnuts. I was curious why this year there are so many and is there a correlation to the severity of the winter and the number of walnuts? We did have a wet spring so they were well watered and probably had lots of pollination of the fruit. We were trying to see if there was on old wives tale if this meant a bad winter :) We just wish we liked to eat Black Walnuts like we do English Walnuts. :) Is there a way to make them more palatable since we have so many or something else to do with the nuts? Is there a quick way to pick them up because we had a friend fall from stepping on one in the driveway and it rolled under his foot? We have to be careful walking around the property doing work because there are areas that are solid walnuts! Thank you for any information you can provide. DB

Black Walnut Overload

The Editors's picture

It sounds like the confluence of climate conditions made your trees exceptionally happy this year. To get them up off the ground, it might be worth investing in a very large plastic lawn rake–they make quick work of large swaths of ground; use a snow shovel to scoop them up and into a wheelbarrow or trash can once you have made piles. As to what the heck to do with all of them–consider baking with them. There are many sweet baked good recipes that call for black walnuts–and we all know sugar makes everything taste better!

Baking with Black Walnuts

Thank you so much for your reply! I think we'll try the baking/sugar idea :) I'll let you know. If you are anywhere near the Kansas City area, I'll be glad to get you a 5 gallon bucket for all your holiday baking needs :)
Thanks again
Diane

Black Walnut trees have a

Black Walnut trees have a slow growing cycle...they will be the first tree to loose its leaves in autumn and the last tree to get leaves in the spring. It has been my observation over the years that they produce nuts on a cycle. It seems like every 5 to 7 years they produce a bumper crop of nuts, then the following year almost none at all...then progressively more and more with each year. If you have an over abundance of nuts this year...chances are that next year you will not have as many.

Overactive black walnut tree - can it be slowed down?

A couple of years ago, my tree dropped a lot of walnuts, but this year it is completely out of control! Yesterday and today, I've picked up over 16 5-gallon buckets full of walnuts off my lawn. I dump them over in a wooded area next to a stream so the wildlife can enjoy them. I didn't know if either a good climate or a bad climate (maybe the tree goes into distress and figures it must reproduce as much as possible) is the reason. Also wondered if because the squirrels climb the tree and eat the walnut, it just keeps producing more and more and more!

A couple of large limbs also broke off yesterday too.

Is there any way to slow this production down? I live in SE Michigan.

black walnuts

these nuts are toxic my puppy ate one that dropped in my yard she got very sick from it how come squirels do not get sick but dogs do i hate those trees

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