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.