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.

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 butternut (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 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 my 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 toxicity. 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:

 

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:

  • Juniper
  • St. John’s Wort
  • Snowball Hydrangea
  • Sumacs
  • Witch Hazel

 

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:

  • Beans
  • Cherries
  • Corn
  • Melons
  • Onions
  • Quince
  • Root vegetables (beets, carrots, parsnips)
  • Squash
  • Stone fruits (nectarines, peaches, plums)

Tolerant Flowers and Vines

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


Plus, 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 me? What if you have established gardens or orchards and cannot move the walnut or the affected plants?

While there is limited success in mitigating the damage from the juglone, 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 cannot 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 from the tree away from plants 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 and 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 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% 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 is a risk.

Why Walnuts?

After 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 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.

Photo credit: Shutterstock.

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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.

10 thoughts on “Death by Black Walnut: The Facts on Juglone Toxicity”

  1. 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.

    • 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!

  2. 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?????

  3. 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.

  4. 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 only crops that can survive. I grow my tomatoes and peppers in pots away from the walnut. It irks me that I have to do this but I have no choice. I have quite the collection of planters now. I’m hopeful the owner will remove the tree, but not holding my breath. I wish people would educate themselves in what is growing in their yard. They could save their neighbors a lot of pain.

  5. 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 trees not far away. I am planning to replant the wild area that is along my property and seems to be growing mostly ragweed. This list gives me some guidance on wildflowers and bushes that can manage being close to the walnuts.

    I have also shared it with my brother who has a young walnut tree growing close to his house where he had planned to also do landscaping. I think he will be moving his tree further back on the property since he has space.

    Thank you.

  6. 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 still love to watch the squirrels in the back yard.

    Yes, we get several black walnut saplings in the spring, but they pull up easily. Unfortunately when we first bought the land, we didn’t know about the juglone toxicity and placed our garden too close to the tree line. After taking a Master Gardener course, I learned which plants were tolerant of planting within 50 feet of a black walnut. Fortunately, I have the land to place my garden far enough away from black walnut trees so I get to enjoy having a garden and having the squirrel entertainment!

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

  7. 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 partner has 40 bw trees that he planted and grafted (sparrow) and 20 pecans.

    Spreading the hulls around the trees is good fertilizer for both those trees and hickory trees, by the way. Also one of the hickories is preferred over the others for a delicious flavored nut. That’s all well and good, but my problem is my organic garden. I see this incredible amount of organic biomass as a positive for my need for compost, yearly. This year I will experiment with 18-month-old hulls, combining them with other things- chicken manure, worm castings, etc. I will gladly share my results with you and your contributors.

    6 a.m. and time for more coffee. The enthusiasm is mounting.

    -John Rabeler

    • 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, and any plants sensitive to juglone will suffer in the vicinity of bw trees or material. If you’re planting berries, root vegetables, squash, beans, and other plants resistant to juglone, they should do well in soil amended with composted hulls!

      Looking forward to hearing more about this project. For more information from a fellow bw composter, see “Black walnut hulls: turning trash into treasure” on the NCR-SARE’s Field Blog.

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