How in the heck can apples and black walnuts grow together? A thought

Last year I traveled to Central Asia to see and (briefly) study the native-wild apple forests  of Kyrgyzstan (article found HERE). Once there, I learned that the forest composition was primarily walnut-apple. This was a bit of a surprise for me to see, because everything I had learned in forestry school told me that walnuts produce a chemical called juglone, which creates a hostile environment for plants that come within contact of walnut roots (as in, it messes with their respiration). Seeing these apples growing happily and harmoniously next to these walnuts was a bit of a mind-blowing experience for me because a thriving apple-walnut ecosystem would have never occurred to me based what I had been told in school.

The walnuts in Kyrgyzstan are known as Carpathian walnuts, or English/Persian walnuts (Juglans regia). They are known to have a lesser amount of juglone than our native black walnut, so I just assumed this was how apples were able to grow in the company of walnuts in these forests. Either that, or the ancient apple genetics had co-evolved to tolerate juglone. Whatever the mechanism was that allowed for these trees to grow together, the results were stunning to me.

The apples in this forest were no-maintenance-flawless and I thought this might be due to a combination of three things: 1.)Excellent genetics (which had co-evolved for over millions of years to resist certain pests and diseases). 2.) The fact that I could smell the juglone chemical being released from the leafy walnut canopy (which acted as a pest deterrent). 3.) The presence of livestock in these forests, which helped keep pest pressure down through disrupting life cycles. After witnessing this, I thought: I have got to figure out how to mimic this apple-walnut ecosystem in the United States.

I decided to start down a path of finding walnut family members that produced a lesser amount of juglone than our black walnut, like hickories and pecans, which wouldn’t kill my apple trees but would still provide the benefits of deterring insects. Though I am still interested in further experimenting with this concept, I’m writing this blog to announce that I’ve discovered another possible pathway… SOIL BACTERIA.

This article has me really excited (warning: it is uber-nerdy): http://amo.colorado.edu/schmidt1988.pdf

Basically, it identifies a juglone-metabolizing soil bacteria which has been known to cancel out the allelopathic properties underneath black walnuts! This would explain some people’s claims that all sorts of plants are able to grow under their black walnuts while others have a barren landscape underneath. This could also explain the relationships in Kyrgyzstan…the native soil could be full of this bacteria and many others like it! All of a sudden, mimicking a wild walnut-apple ecosystem in the US might be made possible by identifying and then inoculating juglone-metabolizing soil bacteria into the orchard(!).

I need to do more research on this, but it would be fund to run a few experiments on identifying landscapes which can grow apples underneath/within the root zone of walnuts and taking a few scoops of soil, in which you then start a new black walnut seedling and transplant out near to an apple.  It’s kind of like fruit exploring, only soil bacteria-meets- fruit exploring.

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6 thoughts on “How in the heck can apples and black walnuts grow together? A thought

  1. Holy crap lady!! That is a big deal! I’m really excited to read this and to hear what you find out about this as we were pretty much relegating black walnuts to a quarantine area on our farm so it wouldn’t mess with the rest of the polyculture but you may have just set it free;-)

  2. I often thinks it goes against the fundamentals of nature to consider any individual plant capable of eliminating all other woody species in an ecosystem. We should consider a law of nature to be “Diversity is Divinity” since nature depends on it.

    I look forward to hearing your progress in this research!

  3. The implications of this thought train are immense. Chestnut blight, amongst other things… Could the chestnuts that get the blight but are then able to wall it off being aided by soil myccorhizae? Who knows. There is soooo much out there to discover, soooo much we just still don’t know. I love that, and I love your joy in exploring.

  4. I’ve seen it as well. We have wild black walnuts here and they grow among other trees with no apparent advantage that I can see. People pick up these bits of information and act ostensibly on the precautionary principal. Here are some more. Urine is too strong/salty to use on your garden, coffee grounds and pine needles are too acidic, wood ashes are too alkaline. Add any of these to the complex and unique system that is any soil or gardening/farming/orcharding system, and in different ways, and it will be found to not be so simple. The walnut tree/apple orchard I saw is very old with the trees seemingly mixed randomly. They looked like they were getting along just fine. The stocks are almost certainly native black walnut, but occasionally trees here will be on Paradox, which is native California black hybridized with carpathian. I haven’t dug to find out where the Juglone suppression idea came about, but it has taken a firm hold in the gardening consciousness. Whatever scientific study or observation spawned it clearly wasn’t comprehensive. Scientific inquiry never is. It just gives us little snap shots of effects under certain conditions, and that is at it’s best. Useful, but limited. The results may or may not be applicable to such complex systems as any given ecology where there are gajillions of factors at play, not just this species next to that species planted in “dirt”. I’m not sure I would plant an entire orchard of alternating black walnuts and apples, but I’m still inclined to think that it would perform just fine. The precautionary principal is supposed to prevent us from doing stupid stuff, but it is often applied much too conservatively. The idea is that if the results could be devastating, i.e. GMO’s, nuclear radiation, then we should err heavily on the side of caution. But if the experiment is not likely to result in devastating outcomes, like putting some coffee grounds on your peas and carrots or planting one apple tree next to a walnut, we might learn something important. That is the flip side, the devastating result could actually be the opportunity or resource that we miss- that we throw away millions of pounds of awesome fertilizer or can plant walnuts and apples wherever we want. This phenomenon of fear based gardening is very prevalent. I haven’t decided if the information age is making it better or worse, but I think it will eventually make it better because of conversations like this one. I was just sent an article yesterday which I couldn’t even be bothered to finish all about coffee grounds and how they shouldn’t ever be used straight and should be mixed with this much lime and then composted with shredded leaves in order to be safe. All of this was based on some speculative pseudo scientific crap about ph measures. Pure speculation. We could expend untold energy and money trying to find the exact scientific truth about what effect coffee grounds have on soil ph under varying conditions and then extrapolate and overthink that into some sort of decision, or try to calculate how much wood ashes, from what species to add to neutralize it so much for growing crop X, or we can dump a bunch of coffee grounds around and see if stuff grows or doesn’t. It does. It grows really well in my garden, and as far as I’ve seen, regardless of the crop or previous soil treatment. I understand the hesitancy more with walnut given that a tree is a longer term investment, but the information gained by taking that plunge could be far more valuable than a couple of trees. Damn, now I want to go plant some walnut/apple experiments just to see what happens!

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