Death by Black Walnut: The Facts on Juglone Toxicity

I grew up in a part of the Nebraska river bottom where black walnut trees (Juglans nigra) were abundant. I enjoyed picking the nut meat from the shells each year, after my grandmother ran the hard nuts over with her car in the driveway!

The black walnut is beautiful, but juglone toxicity may be a problem for other plants. Read more: https://gardenerspath.com/plants/landscape-trees/black-walnut-juglone-toxicity/

While I dreamt of each season’s bounty and Gram’s famous black walnut brownies, I didn’t know that these tasty nuts came with a price.

It wasn’t until my husband and I were well into the landscaping plans of our own 4-acre homestead that we started to notice trouble. Several of our newly-planted apple trees weren’t doing well.

While the cherries, pears, and plums thrived, these poor saplings were wilting, stunted, and sad.

Beloved black walnuts may be a threat to the health of other plants. | GardenersPath.com

The adjacent property had a large walnut tree within 50 feet of our infant orchard. While I had occasionally admired the majestic stature of this tree (and secretly hoped for walnuts to fall on our side of the property line), I didn’t realize that my sudden tree deaths were related to its presence.

Though many I’ve talked to are unaware of its existence, black walnut trees utilize a special survival method that can be fatal to surrounding flora.

What Makes Black Walnuts Toxic?

A chemical known as juglone is the culprit here. Black walnuts aren’t the only trees that produce this no-nonsense defense system, composed of 5 hydroxy-1, 4- napthoquinone. Hickories (Carya) and butternuts (Juglans cinereal) are also to blame, but black walnut trees are known for having the highest concentrations of the stuff.

A chemical from the black walnut can be toxic to other plants. | GardenersPath.com

Juglone is released from virtually every part of the tree, although the roots, nuts, and seeds are the most toxic. This substance serves a purpose in ensuring the survival of the species, but surrounding plants are often subject to unwanted and undesirable consequences.

How Sensitive Plants React

At first glance, the juglone-sensitive plant may appear to be having other issues.

I know that I originally suspected my apple trees were suffering from other maladies. Cedar apple rust is very common here, and it can cause the leaves of apple trees to become mottled and frail.

Black walnut trees are beautiful, but can kill certain plants. Is your garden at risk? Learn more: https://gardenerspath.com/plants/landscape-trees/black-walnut-juglone-toxicity/

When trees started dying, however, I knew this was a cause for concern. Apples 40 feet away from the neighbor’s black walnut were in various stage of expiration. Only the trees growing outside the 60-foot marker, on the other side of our property, were thriving.

If you’re not familiar with the symptoms of juglone toxicity, you may also attribute it to something else.

According to the Morton Arboretum, your plants, trees, and shrubs may exhibit:

  • Wilt
  • Yellowing of leaves
  • Stunted or slow growth
  • Death – sometimes within a few months of exposure

There is no cure for juglone poisoning. The best thing you can do is avoid planting near black walnut trees!

Plants with a Chance of Survival

Not all plants are sensitive to the environment near the tree. But which ones are resistant? If you look at those that grow wild near volunteer juglone producers, you’ll have your answer!

Black walnuts have beautiful foliage but the trees can be toxic to other plants. | GardenersPath.com

When I look outside at the natural, wooded areas of my childhood home, I see plenty of these thriving – often within a foot or two of the trees in question.

Tolerant Trees

Included in the “tolerant” category are the following trees:

  • American Elm
  • Black Cherry
  • Dogwood (includes flowering)
  • Eastern Red Cedar
  • Hickory
  • Locust (most types)
  • Maple (except silver maple)
  • Oak
  • Ohio Buckeye
  • River Birch
  • Sycamore
  • Virginia Pine
  • Yellow Poplar

For the full list, see the Penn State Extension’s guide.

Tolerant Shrubs and Bushes

These shrubs have been identified as resistant to juglone in soil:

The rest of the list can be accessed via the link referenced above.

Tolerant Fruits and Vegetables

You’re safe to grow these around your black walnut tree:

Tolerant Flowers and Vines

The list of flowering plants that can handle being planted next to black walnut is rather long. Enjoy these blooming plants and vines without worry:

Plus, there are dozens of others listed by the Penn State Extension.

Help for Established Gardens and Orchards

So, what if you are in the same situation as I was? What if you have established gardens or orchards, and cannot move the walnut or the affected plants? While success rates in mitigating the damage caused by juglone are low, there are some things you can try.

Juglone Toxicity May Be a Concern if You Grow Black Walnut | GardenersPath.com

Start by ensuring that the seeds, leaves, and nuts of the walnut do not come into direct contact with your sensitive plants.

This may mean installing a protective balcony, fence, or other physical barrier that allows for sunlight and water to come through – but not toxic tree droppings.

In our case, bird netting did keep some of the larger debris that fell from the tree away from plants that were too fragile to be moved right away. If your plants are growing in soil directly above or near the roots of a walnut tree, you can try a raised bed system.

Juglone toxicity caused by black walnut trees can be a threat to other plants. Do you know which ones are at risk? Read more: https://gardenerspath.com/plants/landscape-trees/black-walnut-juglone-toxicity/

While this won’t work for trees or many shrubs, flowers and veggies can be put in a box or container with soil taken from elsewhere. Assuming there is a protective barrier from the soil placed underneath (nontoxic landscape cloth should work), you can keep your soil toxin-free.

One final tip is to keep soil well-drained and adequately watered. Flushing the toxins out of the soil can dilute their effects over time. But this is not a 100% guaranteed solution. The best plan is to keep plants outside of the 50-foot radius that is known to be harmful to them.

It’s also very important that you know where your fertilizer, compost, and mulch come from. Anything that may contain black walnut tree matter poses a risk.

Why Walnuts?

In light of all of this fuss, it may seem that it is just simpler to make sure you don’t have any of these trees on your property.

I strongly disagree with this sentiment. I grew up with these majestic trees providing wind protection, shade, and tasty nuts every year.

They have a long history of affecting the environment in a positive way, and I believe they should be accommodated, if possible.

On the other hand, not everyone has the space to allow for such a fickle tree.

Did you know growing black walnut trees can be a threat to certain plants? Learn more: https://gardenerspath.com/plants/landscape-trees/black-walnut-juglone-toxicity/

If your lot is particularly small, and you do decide that the tree has to go, be mindful of the roots. They can stay in the soil for years, continually releasing juglone into the surrounding area until they finally completely their decay process. Ridding yourself of the great walnut may not be the total solution you were looking for!

Do you have one of these trees in your yard or on your homestead? We’d love to hear about what you’ve done to create an ecosystem where both tree and garden can coexist.

Also, am I the only one with fond memories of shelling the hulls in the driveway? Share your black walnut memories in the comments.

Don’t forget to Pin It!

Have you heard of juglone toxicity? This side effect of keeping black walnut trees may be killing your other plants. Learn what fruits and flowers can withstand living near the tree and how to properly treat sensitive plants with our owner’s guide on Gardener’s Path.

© Ask the Experts, LLC. ALL RIGHTS RESERVED. See our TOS for more details. Uncredited photos: Shutterstock.

About Linsey Knerl

Born and raised in a small Nebraska town, Linsey Knerl is a homeschooling mother of six who enjoys blogging and working hard on her 3 1/2-acre Nebraska homestead. When she’s not working on her next fantasy novel, you will find her in her kitchen, perfecting the Danish recipes of her grandmother with those special ingredients you can only find in a backyard garden.

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Linda
Linda (@guest_1493)
2 years ago

Thank you for spacing guidelines. I moved to the western North Carolina Mountains 4 years ago. Immediately, I planted a small orchard not realizing the beautiful 40′ tall tree about 60 ft away, just over the property line, was a Black Walnut.

So far our two closest apple trees have been unaffected. My husband removed the BW limbs extending over the property line in order to reduce leaf and nut dropping. We are considering moving the young apple trees to a safer location.

We have a BW on our acreage, too, about 20 ft from the vegetable garden. No problems there.

Allison Sidhu
Allison Sidhu (@allison-schultz)
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Reply to  Linda
2 years ago

Good luck to your and your apples, Linda! They are beautiful, though they can be messy. When I was growing up we had black walnuts within proximity of our vegetable garden too, as well as tall tulip poplars and other trees. Struggling to grow in what was mostly a shade garden seemed to be much more of an issue than any potential problems from juglone!

a Rickan
a Rickan (@guest_1607)
2 years ago

Planted 12 cedar trees along the rear property line — three on each end do good but the middle six are always dying. Then I was told it is because there is a Black Walnut tree just inside the neighbor’s property next to the cedar trees.

The end ones are over 8 ft tall and twice as big as the center six trees closest to the walnut trees. Does this sound like the reason for the failure of the centre trees?????

Holly
Holly (@guest_1993)
1 year ago

No fond memories here, just messes of staining leaves, staining nuts, dodging the falling hard nuts bombs, and sharp cracked shells that hurt your feet from my neighbor’s tree. They don’t belong in a city yard, especially on a property line.

Ana
Ana (@guest_2115)
1 year ago

My story involved a black walnut that sprouted in my neighbor’s yard. However, because it is growing in a corner where 4 backyards meet – a spot that affects my garden and my neighbor’s – my hands are tied. It is now too big to remove without professional help, which the owner has clearly refused to do. I’ve learned to grow crops that can survive near the walnut tree. My neighbor, on the other hand, is trying to raise his soil and water but I can see his tomatoes are all wilting. Eventually, he will learn like I did. Grow… Read more »

Jeff
Jeff (@guest_4688)
Reply to  Ana
11 months ago

That is not the only option. You can kill it from your property which is ok where I live. I killed our neglectful neighbors walnut tree by severing the roots to my good soil and bought the wood for $200. His neglected tree comes down and I get a ton of walnut is a win win for me.

Sheri
Sheri (@guest_2386)
1 year ago

Thank you for this info. I also grew up in Indiana with a Grandma who would rake her walnuts into the driveway to help crack them. It is a delightful memory. I recently moved to where I live against a wild wooded area and there are a lot of walnut trees. A squirrel must have planted one directly on my property line because I just identified it and it is 5 ft + tall. It is in a bad spot and beginning to grow crooked, so I will be removing it, but this made me mindful of the other mature… Read more »

Suzanne
Suzanne (@guest_2754)
1 year ago

We have several acres of wooded land scattered with black walnut trees. There are a few along the edges of the woods where we get to enjoy the squirrels. It is quite comical to watch the squirrels bury their walnut, dig it back up, move to another spot and look around like they think another squirrel is watching and going to steal their treasured nut. The squirrels will do this for 30-40 minutes; digging and burying the walnut, then digging the nut up to move to another spot to bury it again. My grown children remember these entertaining events and… Read more »

Allison Sidhu
Allison Sidhu (@allison-schultz)
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Reply to  Suzanne
1 year ago

Thanks for sharing, Suzanne! It’s excellent that you have enough space to enjoy both the squirrels and your garden. 🙂

John Rabeler
John Rabeler (@guest_3123)
1 year ago

5 a.m., 2/7/19, got my coffee, Youtube, and you. Problem solving: how do I turn a negative into a positive? I have 240,000 pounds of bw hulls, after becoming a huller for Hammons bw co, in ’17 and ’18. I hulled 40,000 pounds by myself in ’17, and in ’18 I got a partner who is retired, like me, and we hulled 80,000 pounds. Our goal this year is to do 160,000 pounds. Since the hulls weigh twice as much as the nut you can easily compute we will have 320,000 pounds of hulls from this year’s hulling. Luckily, my… Read more »

Allison Sidhu
Allison Sidhu (@allison-schultz)
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Reply to  John Rabeler
1 year ago

Wow, that is a lot of hulls, John! You’re absolutely correct that both hickory and pecan are tolerant since they both produce juglone as well, though in lesser concentrations than bw. As for including the aged hulls in compost for organic gardening, just be sure to keep in mind which plants are tolerant as well as the needs of your soil. Composted hulls are alkaline (sweet). Worm castings are always wonderful, and chicken manure is high in nitrogen and can be great for leafy plants, as long as it is aged. The fresh stuff tends to burn and cause damage,… Read more »

Suzie Hivnor
Suzie Hivnor (@guest_3815)
1 year ago

We have several black walnut trees in the yard and a few along the fence line out along the back 40. The squirrels love them, bury them, dig them, leave holes everywhere in the yard. The dog doesn’t like nearly getting hit in the head by a falling nut while watching the squirrels in the branches. We have run them over, busted them open with a vice, but we don’t really have a harvest. We have our taste and allow the rest to go to nature. I have a dogwood and a purple magnolia I want to plant near a… Read more »

Allison Sidhu
Allison Sidhu (@allison-schultz)
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Reply to  Suzie Hivnor
1 year ago

They can be a nuisance, can’t they? I remember having to dodge the barrage from above as a kid, and then gathering them from the driveway with my brother for his experiments with making natural dye in buckets in the garage. When the trees are mature, those nuts fall from quite a height!

As for the lamium- how interesting! Lamium is usually regarded as a plant that does well within range of black walnut. Do you know if you had spotted deadnettle, or some other variety?

Gavin
Gavin (@guest_4309)
1 year ago

If I plant a black walnut tree in a pot, will the water run off from the pot contain juglone and kill my plants nearby?

Rkg
Rkg (@guest_4332)
1 year ago

I find this tread particularly interesting. It appears that Walnuts in addition to the trees resistant to this toxin appears to be some of the favorites to the Chinese Lantern Fly that has been invading parts of Pennsylvania.

Michael Martin
Michael Martin (@martqbd)
11 months ago

Great article. 1 more reason to get rid of the huge BW. We had to get rid of a pony and a jackass because I found out about the tree being toxic to them. So I planted a small apple orchard there this year. I keep hoping it will fall over because it keeps leaning. I just need to cut it down.

Wendy Schmidt
Wendy Schmidt (@guest_4704)
11 months ago

I have a small one growing in the middle of my garden. Just sort of inherited the thing when I moved here two years ago. Immediately gardener friends told me to get rid of it. But, I found out that most Prairie Plants do find around it. The problem for me is actually the growing tree throwing shade and blocking out the sun. I intend to trim branches every winter in the hopes it will not happen. It’s about 10 feet tall right now so not very big. But, I’ve heard it can grow 3 to 4 feet every year… Read more »

Kris
Kris (@guest_4755)
Reply to  Wendy Schmidt
10 months ago

I’m debating on cutting down our 20ft+ black walnut..its growing within 15 ft of two very mature apple trees. after reading this article I’m not sure how they’re still alive but they actually seem to be doing okay..
At this point though I’m scared of the ramifications of the black walnut I would definitely prefer all the fruit trees to be here as opposed to the walnut….any input would be greatly appreciated.
They are all beautiful mature trees I would just hate for some of them to start dying off because of the BW😥

Mary Lou Burke
Mary Lou Burke (@guest_4852)
10 months ago

We planted a Green Giant Arbovitae next to a Black Walnut. It is dying. If we remove it and move it can we possibly save it or is it going to die? We had been told they are tolerant but maybe just too much too close? Help!

Allison Sidhu
Allison Sidhu (@allison-schultz)
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Reply to  Mary Lou Burke
10 months ago

Unfortunately there is no cure for juglone poisoning once plants are affected – but arborvitae is generally considered a good companion for black walnut. What symptoms is it exhibiting? Perhaps something else is the culprit.

hazel
hazel (@guest_5044)
Reply to  Allison Sidhu
9 months ago

we just cut down a black walnut to keep the squirrels from getting the nuts and creating more black walnuts. it took days to get all the nuts and deal with the branches for it was 50 or 40 feet high. It grew from a small bush that i trimmed up, not knowing what it was. We have a pickup truck bed full to the brim with the nuts. it would take a lifetime to hull them and crack them. but i feel some victory over the tremendous power of the tree. it was towering over the roof of a… Read more »

Allison Sidhu
Allison Sidhu (@allison-schultz)
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Reply to  hazel
9 months ago

Those hulls are tough, but they will soften if you give them some time. An old fashioned hammer and chisel will work for manual hulling, and in bulk, some growers even like to run them over with their trucks. My stepdad suggested this once when I brought a precious package of macadamias home to Pennsylvania from California- another tough nut to crack! But with a whole truckload, you might want to consider bringing them to a huller and selling them by weight. Depending on your location, this option may be available to you. I’m not sure whether some of the… Read more »

Allen Kaiser
Allen Kaiser (@guest_5098)
9 months ago

My beagle loves tossing around the walnuts that fall from the neighbor’s tree. Last night she was up vomiting every 10 minutes for 8 hours and was so weak I thought she would die. Couldn’t figure what caused this until I googled effects of juglone on dogs. Seems it’s extremely toxic to dogs and is responsible for many deaths, liver and kidney failure. My neighbor has refused to remove the tree. My only recourse now is to comb the yard daily and remove the nuts that fall in my yard and nuts the squirrels bury in the yard. Walnut trees… Read more »

chris skourtis
chris skourtis (@guest_5469)
7 months ago

We just bought this city property with a huge-oversized ,majestic sculptured backyard (previous owner spent alot of money there) with two man-made ponds …..full of ornamental rock walkways etc…..We just found out our beautiful backyard of 15 trees of which 6 are black walnut….We have kept our dog from the backyard since the move….me , I love the trees(all mature) and don’t want them touched, as the squirrel action is lovely…..my wife wants to cut them down(dog comes first)….is there a way dog and trees can co-exist?

Allison Sidhu
Allison Sidhu (@allison-schultz)
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Reply to  chris skourtis
7 months ago

Congrats on the new purchase! Sounds like a beautiful yard.

Black walnuts can be harmful to dogs, particularly if they ingest fallen nuts that have started to mold and rot. It won’t be easy, with six trees on the property, but diligence is key here- if your dog likes to explore the world with his/her mouth and just can’t leave the walnuts alone, you’ll need to pick up the nuts as they fall. Laying tarps beneath the trees during the fall can be helpful, for easy pickup and removal.

Bren
Bren (@guest_5719)
5 months ago

I live in an urban environment and have an 80+ year black walnut tree on my small rectangular lot. The tree is at least five stories high and is located in the backyard where I’ve held our dog playgroup every Saturday for the last four years. None of our 10-13 weekly dog guests have ever shown signs of being poisoned from the toxic tree roots, sticks, fallen leaves and walnuts (knock on wood :-). The dogs are different breeds and range in age. Of course, I didn’t know Black Walnuts were toxic to dogs back when I formed the playgroup.

Tracy Raynolds
Tracy Raynolds (@guest_6397)
2 months ago

Thank you for the informative article. I had planned to add the rot from a disintegrating stump into the combo. Now I will not. We too so enjoyed the nuts from the tree but it was huge, old and eventually had to be removed. As for the driveway method of cracking nuts, yes we had the same. But most interesting were the crows picking nuts, then dropping them onto the driveway to crack them open; then, of course., competing to see which bird could get there first! Really fun to watch.
Cheers, Tracy Raynolds

Suzette
Suzette (@guest_8345)
8 days ago

We have a black walnut tree within 10 feet of our home. This year we did 3 container tomato plants on our back deck to notice curled, drooping leaves and a darkening of those leaves almost like a soot but it does not rub off. I have container herbs near those tomatoes and those are fine. Is juglone airborne where it could be affecting my tomato plants or could it be something else?

Allison Sidhu
Allison Sidhu (@allison-schultz)
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Reply to  Suzette
3 days ago

Juglone isn’t airborne, though any leaf matter or nuts that fall into the containers would contain juglone that could leech into the soil. It sounds like your tomatoes may be experiencing an unrelated issue. Leaf curl or leaf roll can be caused by dry weather or inadequate watering. Are the leaves black all over, or do they have spots? It sounds like the problem may be septoria leaf spot, or perhaps early blight. Container-grown tomatoes need to have enough room for their roots to spread, so planting in large, deep containers is recommended. They need to have adequate drainage holes,… Read more »