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Walnut as a weed suppressor

 
Matthew McCoul
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Location: Southeast Michigan
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http://hort.uwex.edu/articles/black-walnut-toxicity/

This page, among others, makes a pretty good case for a black walnut in a forest garden.

While there's a good list of things that won't grow near black walnuts, there's also a good list that will. I intend to try and grow a polyculture of the resistant species around the walnuts on my property.

My thoughts are that the juglone will help suppress anything I'm not growing there.

Does anyone have experience with this? Any thoughts?
 
Cristo Balete
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Aside from the hulls staining everything, making a mess, it seems that humans don't do well with juglone, either.


" reduces viability of human cells in culture"...." Normal fibroblast were found to be especially sensitive to juglone and lost viability primarily through a rapid apoptotic and necrotic response"..."Furthermore, juglone inhibits mRNA synthesis in human fibroblasts in a dose-dependent manner. Surprisingly, juglone caused a drastic reduction of the basal level of p53 in human fibroblasts/..."..."Our results show that juglone has multiple effects on cells such as the induction of DNA damage, inhibition of transcription, reduction of p53 protein levels and the induction of cell death"

http://www.ncbi.nlm.nih.gov/pubmed/16271620

If the hulls are left to rot in the soil and create higher levels of juglone, and plants planted under the walnut get their roots into the root zone of the walnut, they are likely to uptake it.

If walnuts are planted on the edge of a garden, and the hulls are not left to break down in the soil, and no plants are planted under them, then eating the nuts isn't a problem. They get really big and create a lot of shade anyway, so that's something to consider, even if you want to still plant under it.
 
Matthew McCoul
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You may have misunderstood me.

I'm *hoping* the plants will take up juglone by *intentionally* leaving the hulls.

The idea is to only grow juglone-tolerant plants in that location, of which there are many.
 
Cristo Balete
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I thought I saw the plants on the juglone-tolerant chart to be vegetables, things you eat, beans, beet, carrot, corn, melon, onion, parsnip, squash. They would have juglone in them. I guess if you only want to put landscape plants under it, it wouldn't matter. But those hulls stain everything, they make a real mess.

Thick, heavy mulch suppresses just as many unwanted plants and it improves your soil to boot.
 
Rose Pinder
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"They would have juglone in them"

Do you know that for sure?

"But those hulls stain everything, they make a real mess."

I think that depends. Most of ours dropped on the drive and I just kicked them into the garden while green. They didn't cause any staining and were no more problem than anything else that trees drop. You wouldn't want them dropping on a patio or lawn that was in use a lot, but other than that they seem fine to me.


That's a great resource list thanks Matthew. I haven't done what you are proposing, but have observed what grows under and around a 15 year old single black walnut where I used to live. It had a silver birch next to it that did very well. Under them were some mid sized local native shrubs that were fine. Couch did creep in from the silver birch side, but it was worse under the birch and much less of a problem under the walnut. There was always deep leaf litter so weeding was easy enough, and much less than in a garden or orchard. Just inside the drip line I had some perennial herbs and annual wild herbs that did ok, nothing spectacular but they weren't getting watered either. Some of the annuals did grow right up to the trunk of the walnut.

How close are your walnuts? (eg close or with gaps?). What you are suggesting sounds good to me.
 
Cristo Balete
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Rose, yeah, they uptake the juglone, otherwise it wouldn't kill some plants. It isn't from the hulls hitting the exterior of a plant that some plants die being within 50-80 feet of a mature walnut.

Here's something I read: "Many plants such as tomato, potato, blackberry, blueberry, azalea, mountain laurel, rhododendron, red pine and apple may be injured or killed within one to two months of growth within the root zone of a black walnut."

That's pretty quick.

But committing to a big tree changes that area for decades. In the case of a walnut it could be the rest of our lives. Adding something permanently to the soil where we want to grow food, unless we're absolutely sure we want that there forever, it's a lot easier to be able to change our minds and experiment with different things.

We want to feed the soil, feed the plants, and I'm not sure adding a growth inhibitor is the best way. I always get rid of growth inhibitors because they don't differentiate. The chart on Matthew's link says plants "tolerate" juglone. That doesn't mean the plants will thrive. They may only be able to be 50% of what they could be. But you won't know that for several years. You get immediate results with thick mulch suppression and soil that is more alive.

A walnut tree is a great tree for what it produces, it can add value to a property. But I figure I've lost enough brain cells in my lifetime, I don't need to add juglone to anything!
 
Cristo Balete
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Here's something else in that article:

"The area affected extends outward each year as a tree enlarges. Young trees two to eight feet high can have a root diameter twice the height of the top of the tree, with susceptible plants dead within the root zone and dying at the margins. "

"Horses may be affected by black walnut chips or sawdust when they are used for bedding material. Close association with walnut trees while pollen is being shed (typically in May) also produce allergic symptoms in both horses and humans."

Juglone will eventually break down if the parts are composted, it just takes time:

"Walnut leaves can be composted because the toxin breaks down when exposed to air, water and bacteria. The toxic effect can be degraded in two to four weeks."

"However, composting of bark for a minimum of six months provides a safe mulch even for plants sensitive to juglone."

"finished compost tested for toxicity by planting tomato seedlings in it"

http://ohioline.osu.edu/hyg-fact/1000/1148.html
 
Rose Pinder
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I think you are conflating some things and extrapolating others in ways that aren't necessarily true. eg taking a lab experiment of a single, isolated constituent and its effect on cells in vitro (and we're looking at an abstract only, not the actual research) and suggesting that that same chemical is taken up by plants and then has the same toxic effect on humans eating those plants is a pretty big leap (it's also a bugbear for herbalists who see these kinds of unfounded suppositions made all the time. Herbs can work very differently as a whole plant than as an isolated chemical, and can work differently in humans compared to petri dishes).

I'm also not sure why you are assuming that the secondary plant is taking up juglone into its edible parts, as opposed to say its roots being affected. Or that that is why it won't grow there. Or why the plants that do grow there are less affected or completely unaffected, and whether they are taking up juglone into the parts that would be eaten.

Taking a part of the walnut tree that has juglone that doesn't break down for a time (eg bark chips) and getting an allergic reaction to topical exposure, or to eating it directly (do we know which for the horses?) is not the same as getting poisoned from eating a secondary plant that may or may not have any juglone in it.

Different parts of the black walnut are used in herbal medicine, including parts that are high in juglone. I'm guessing that some parts are used for the specific reason that the juglone has an effect. In that case, dose makes the poison or not.


btw, I took from Matthew's opening comment that the black walnut trees are already on his land and he's looking at planting around/under them.
 
Rose Pinder
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Matthew McCoul wrote:

My thoughts are that the juglone will help suppress anything I'm not growing there.



Just rereading that, what is growing there already? I've seen grass growing under black walnuts in parks, so they're not going to necessarily deter that.
 
Joseph Lofthouse
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I gather the Carpathian walnut leaves and nut husks in the fall, and mulch under the grapes with them. I don't ever have to weed under the grapes. I suppose it's a combination of the walnuts and the deep shade that the grapes produce. Perennial onions, and raspberries grow under the grapes.
 
Cristo Balete
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I've seen plenty of grass under walnut trees, too. So some weeds are also tolerant of juglone as well. When I was a kid it was my chore to pick up all the fallen fruit and run the tractor around the fruit trees. There was never a time that I didn't have to go under the walnut tree in spring and summer.



Rose, I guess it's just better to be informed and make an informed decision. The world isn't black and white. It doesn't *always* happen, or *never* happen. There are shades of gray in all things. People have been warned about cigarettes, and there's plenty of smokers out there, but they can't say later they weren't told.

If you're finding peer-reviewed research that says juglone doesn't cause any issues in humans, it would be good to read that.

I'm also not sure why you are assuming that the secondary plant is taking up juglone into its edible parts, as opposed to say its roots being affected.


We know it's not the case that plants take up high nitrate fertilizers, pesticides and weed killers into their stems only, and not into the fruit or vegetable part we eat. Otherwise why would we bother with organic food? Why would we bother with hauling all this manure and mulch and soil amendments? It would save time, money and our physical selves to just go buy a bag of fertilizer with weed suppressant in it, and throw it around in about 15 minutes for the average garden, water it in, hey, we're done. Organic gardeners stopped buying and eating fruits and vegetables grown this way long ago.

Since plant roots uptake water, whatever is in that water goes throughout the whole plant because plants are 90% water. A tomato is 90% water, it got that water from the stems. There's just no way around it.







 
Joseph Lofthouse
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Juglone is a plant pigment that is dark brown in color... If it were entering my grape plants, or mint, or onions in high quantities, then I'd expect the foods that I grow in the walnut leaf mulch to turn brown. Juglone tastes extremely bitter. If it were entering my food grown in the walnut leaf mulch in high doses, then I'd expect the food to taste bitter.

Juglone is slightly soluble in alkaline soils, but not in acidic soils. It's solubility in water is only about 50 parts per million... Juglone binds with proteins and other chemicals which is what makes it such a good dye. So the juglone may or may not be soluble in the water around a plants roots. And even if it does enter a plant, the dosage is extremely low.
 
Cristo Balete
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The article I quoted about health effects on humans concerning juglone was published on the National Institutes of Health Website, in PubMed. It is a scientifically researched, peer-reviewed article that has some findings that were gathered by the highest scientific standards we can come up with. Whether people want to believe it or not, it's up to them. Whether it's enough to make a difference, it would take a lab to tell you the levels.

Walnut tree husks contain both the dye component, which is a phenol, and the juglone, which is an oil made up of quinones. If seeing the brown dye in plants that did uptake juglone was how it chemically worked, then all the leaves on a walnut tree would be brown, and they are not. Maybe someone here can give the chemistry at the molecular level, and explain the mechanism of action of juglone.


Here's the chemical description of juglone:

http://www.chemfaces.com/natural/Juglone-CFN90497.html



Here's a description of using husks and leaves if you want to dye things:

http://home.onemain.com/~crowland/Pages/Walnut.html


Here's how juglone kills lettuce seedlings at the root level:

http://www.sciencedirect.com/science/article/pii/S0981942814002770


 
Todd Parr
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I can only add this to the discussion: I have two walnuts trees. Grass and many kind of weeds are growing all around the trees and right up to the trunks. The trees may suppress the growth of some things, but no one told any of the grass and weeds that grow on my land.
 
Sean Henry
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I have been working on gathering a list of plants that are and are not tolerant of juglone since the property that I purchased last year has several acres planted in black walnuts.

I rushed to post the list I have created from about a dozen sources. In the future I will update the formatting and add more information such as what is edible but for now here is a list of plants and juglone tolerance.

I would post the list here but it is a bit long.
 
Russell Olson
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Cristo Balete wrote:The article I quoted about health effects on humans concerning juglone was published on the National Institutes of Health Website, in PubMed. It is a scientifically researched, peer-reviewed article that has some findings that were gathered by the highest scientific standards we can come up with. Whether people want to believe it or not, it's up to them. Whether it's enough to make a difference, it would take a lab to tell you the levels.

Walnut tree husks contain both the dye component, which is a phenol, and the juglone, which is an oil made up of quinones. If seeing the brown dye in plants that did uptake juglone was how it chemically worked, then all the leaves on a walnut tree would be brown, and they are not. Maybe someone here can give the chemistry at the molecular level, and explain the mechanism of action of juglone.


Here's the chemical description of juglone:

http://www.chemfaces.com/natural/Juglone-CFN90497.html



Here's a description of using husks and leaves if you want to dye things:

http://home.onemain.com/~crowland/Pages/Walnut.html


Here's how juglone kills lettuce seedlings at the root level:

http://www.sciencedirect.com/science/article/pii/S0981942814002770



I think it's fair to consider alot of perspectives when it comes to science, but a quick pubmed search of Juglone brings up numerous peer reviewed papers citing Juglone as potentially anticancerous, antibacterial, and antiviral.
Human cells in culture are not the same as human cells(in a human). Cells in culture are such an artificial phenomenon, certainly useful for science, but also difficult to correlate to actual human bodies.
I'm not saying Juglone is non toxic, but I think any edible that is grown in the presence of Juglone is fine. After all walnuts themselves are incredibly good to eat.
My black walnuts have had a bumper crop year, and they do suppress lots of plants around them including grasses. The wife has had trouble growing anything "pretty" in our backyard due to the tree's presence. Forsythia seems to have made it a whole growing year without issue.
 
Cristo Balete
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I think it's important to make the distinction between juglone that gets into the soil around the tree, and that comes from the hundreds of green husks that turn black that rot off the shell. They are what contains high levels of jugline, in addition to the roots of the tree. And if year after year after year those rot into the soil, that is a major source. It's not about the nut meat inside the shell having juglone.
 
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