Allelopathy that damages fruit trees

It is not a grafted tree. And it is very much a black walnut tree.

I agree that Allelopathy is not well understood. What I am objecting to is blanket statements like “Black walnut trees are toxic to anything growing under them”. These are invalidated by my observations.
I think there might be circumstances where black walnuts are toxic. It is important to identify those rather than paint with an excessively broad brush.
A single counter example disproves a false theory. So anecdotal experience is definitive in this regard.

Further my soil could be characterized as clay. Almost all native soil west of cascades in rocky clay.

Not all black walnuts are necessarily equal, according to Richard. One question is whether yours is an Eastern black walnut, not whether it is a black walnut. The EBW range is not west of Texas. Ca. black walnuts are naturally semi-dwarf trees, so obviously have much less aggressive root systems. You say yours is large, however- do you mean 70’ or 20’? 70’ is large.

The sandy soil thing was just an example of variables that are in the mix. A clay soil has its own characteristics that might have an affect also (such as a less extensive root system). No one is saying that every black walnut tree produces enough poison to be damaging to all other plants under it in every situation. Did someone make that statement on this topic?

At any rate, I don’t mean to nit pick and your contribution is helpful. I just would like to know if you are sure that your black walnut is an Eastern one.

How would you like me to proceed? Would some photographs of the tree and leaves and plants thriving under it suffice?

I’m just asking why you don’t think it is a CA black walnut, given you are in its natural range- people don’t plant Eastern black walnuts as ornamental trees, they are generally only available as grafted, selected varieties. They don’t have much difference in appearance besides the relative I don’t see how a photograph would help.

  1. It is a juglans Nigra. I have harvested the nuts and showed it to experienced people. (Who run nurseries)

  2. Tree is around 80 feet tall and had a massive spread before I had it pruned. It is bigger than most city size yards around here.

  3. Lots of people grow them as shade trees around here. Do you only grow native trees? People have been growing non natives for centuries. Nearly all fruit trees (apples, pears, kakis) are non native to US. You might even be growing a few non natives.

It appears you have made up your mind on the allelpathic effects of black walnut and don’t want to see evidence to the contrary.

I don’t know the details of Juglans nigra. But I have read a lot about Allelopathy over the decades and contrary to what has been stated here, I believe it is a well-researched subject. All Allelopathic plants drop one or more toxins to which they are immune. Some culprits (e.g., California pepper tree) put out a general purpose root toxin. Others – I believe eastern Maple put out a more specific toxin that is detrimental to their historical competitors.

What we know and love as “fall colors” is allelopathy in the large. It is warfare!

I was only trying to determine if you were actually growing an eastern black walnut, which I wasn’t clear on until now. I thank you for making that clear, but I wasn’t trying to engage in combat. If you mentioned how tall it was previously, I must have missed the fine print.

While I disagree with Richard’s statement that allelopathy has been widely studied, there have been some studies(widely is a subjective word but a quick search reveals that there are qualified folks who disagree with Richard’s use of it), A lot of the claims in the literature about specific plants being vulnerable to juglans ARE based only on hearsay, from what I’m reading, but here is a legitimate study. Black Walnut Allelopathy in a 28-Year-Old Loblolly Pine Stand and … Can’t link the download to this page, but search with those words and you will find it. There are more, but maybe none that pertain to the species in your own yard. Blueberries are apparently on the list of studied plants, and I’ve had blueberries die with unnatural speed when planted under them.

Apparently, apple trees have been determined to be adversely affected- at least in some conditions. My own limited experience suggests that in some soils many common orchard species are adversely affected but in some soils they are not. Of course, my observations are only circumstantial evidence, not proof and could be a coincidence. I’ve never cut down a BW tree in such an instance and studied the results.

At any rate, black walnut trees are not what I intended to be the primary focus of this topic- I don’t mind the diversion but I find the battle between prairie species and forest species to be more interesting. I’m not managing any fruit trees near black walnuts these days.

Thanks for the clarification of your intent.
I am including some photos for completeness so that we have some actual data on the thread rather than oft repeated quotes about allelopathy associated with black walnut. In fact simply searching for allelopathy on google brings up several links on Juglans Nigra.

The first photo is that of the tree itself, the next two are of the leaf structure and of the fruit. The final one show a Rhododendron growing vigorously around 3 feet from the tree trunk.
Rhodies are supposedly very sensitive to black walnut.
I also have a large fig tree growing in the trees dripline.

Grass grows fine under the tree.

To me, the western red cedar is far more toxic than Juglans Nigra. Nothing will grow under it.

In all fairness, I didn’t really think you had an eastern black walnut either, but my thought had little to do with the correct ID of your tree.

I just didn’t think someone would say to themselves, “Oh yes, I want to get my hands on one of those non-native eastern black walnuts. I love their weedy growth habit, their shells that rival steel for hardness, and their inferior nuts that stain my hands black. Oh boy, where can I get one?”

Then again, where I grew up, black walnuts were essentially trash trees, so I may be biased. :wink:

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I think you might be biased :slight_smile:

I see them around here quite a bit. I wouldn’t have planted it. But it came with the house and is a beautiful (if messy) tree.

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As you likely know, there are selected varieties of the species with the same growth habit, but with thinner shells and much better nut to shell ratio. Here. where they are native, I believe that they are rarely sold by nurseries as seedling trees for landscapes. They are invasive in that they send up saplings from root suckers. Their natural habitat is near stream beds or marshes- at least, in the northeast. Our native hickories grow larger here and tend to be much more attractive trees to my tastes. They don’t compete with BW.s and tend to grow in better drained conditions.

BWs probably became popular there because their poison is not toxic to turf and they allow adequate sun below to keep the grass healthy.

It is interesting that they are not lethal to rhodies, because they are in the same family as blueberries, but not too surprising. However the myth that they are poisonous to them may have come from that association. When you’be been in the dirt and literate for as long as I have been, false horticultural information passed off as established fact never comes as too great a surprise. Dr. Carl Whitcomb achieved his reputation by researching established horticultural myths and proving them false. I wish there were more in academia like him. .


Have harvested black walnuts off and on for 50-something years…never saw any “root suckers”.
I also don’t consider black walnut meats as “inferior nuts”. They are just more trouble to harvest and crack. I’d prefer a good black walnut to an English Walnut for a snack or to cook/bake with.

Have intentionally planted black walnuts in yards a few times…

Currently have a couple seedlings removed from somebody’s flower bed potted up in one gallon container. (And, this year, I’ve also sprayed Crossbow on some that were planted by squirrels in places they were not welcome.)

Black walnuts and rhododendrons won’t get along well…but might survive if the rhodie is in a raised bed away from the roots.


Agreed, especially in candies, they’re great. You’re not likely to grab a bowl and a hand cracker and snack on 'em though…

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I think Black Walnuts have a more complex and interesting flavor than English Walnuts. But I can see why some may not like them. They also spoil more quickly-I’ve found.

But they are really a pain to crack and pick. And they stain very badly.

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We had black walnuts all over when I was a kid. My folks and grandma just loved the things. Ma and Grandma would put them in all kinds of baked goods…which really ticked me off. I cannot stand black walnuts :confounded: Nasty, musty, gross

As far as them being allelopathic. My anecdotal observations are that they are indeed. I personally lost peppers, tomatoes, apples, and pears when I made the mistake of planting them anywhere near a walnut tree. Black walnuts have no value to me.

There are plenty of selected varieties with thin shells and a higher ratio of meat to shell,

They are sweeter than Walnuts and also have that intense juglians flavor. Interesting nut. If I had more land I’d grow them.

Persian walnuts have a slightly bitter flavor on the pericarp. Black walnuts can have a bad flavor if left in the husk while it decays. Harvest them when the nuts are mature but the husk is still green, remove the husk immediately and wash them thoroughly with water. Dry them thoroughly for about 3 or 4 weeks. The result is a superbly flavored nut with a ton of uses for fresh eating and cooking. If anyone is seriously interested in growing black walnuts, I can provide a list of varieties and suggest root stock sources. For most of the Southeast including Tennessee, Alabama, Georgia, etc. Thomas, Farrington, and Neel #1 are outstanding.