We’d like to grow apples on this site. An apple / black walnut forest with the walnuts as the canopy tree and apples as the understory tree sounds beautiful, productive and delicious. Unfortunately, it also seems unlikely. Genus Juglans (walnut species) all produce juglone, a chemical that inhibits the growth of certain plant species, and black walnuts produce the highest juglone concentration of them all. Genus Malus (apple) unfailingly shows up on reputable lists of juglone-sensitive fruit trees and is consistently omitted from the often short lists of juglone-tolerant fruit trees. Black walnut trees aren’t inclined to share their habitat with apple trees.
Another tree that is consistently reported as juglone-sensitive is basswood, also called a linden tree. And at the north end of this site, there is a large basswood tree happily growing next to a black walnut tree. Presumably that shouldn’t be happening. Apparently our basswood missed the memo.
Seeing a basswood tree growing right next to a black walnut tree in a black walnut dominated treescape caused us to wonder if it was really impossible for apple trees to grow near black walnuts. Perhaps some heritage varieties could make it even if most commercial apple varieties consistently succumb? Our basswood’s success was inspiring enough that in 2017, we ordered and planted 24 apple trees. Most were heritage varieties and we also included a couple of varieties that had been recently developed and released. We planted three each of Brown’s Apple, Florina Querina, Galarina, Ashmead’s Kernel, Newtown Pippin, Harrison, CrimsonTopaz and Zestar! around the site and then waited to see what would happen.
They mostly died. Some held on for a few more years than others. Whether it was the juglone or siting issues or something else that caused them to fail is hard to say but the dismal survival statistics imply that overall, this property is not a site where apple trees want to live. This tree that lived, an Ashmead’s Kernel, is the one exception. (picture)
Could this apple tree variety have some small capability to tolerate juglone that the others did not? It would be exciting if that were the case. If an apple variety was exhibiting odd behavior, it wouldn’t be surprising to learn that it was an Ashmead’s Kernel. Ashmead’s Kernel is a variety which dates back to the 1700’s, one of the few apple varieties from the Old World that succeeded in the New World with a dubious claim to fame of irregularly producing notably unattractive but exceptionally tasty fruit (Orange Pippin Ltd., 2022). No one would confuse an Ashmead’s Kernel apple with a modern commercial variety.
Apple seeds don’t grow true. Plant an Empire apple seed and what will grow is something that is not an Empire apple. Named varieties of apples are grafted and so all Ashmead’s Kernel trees have virtually identical genetics, as do all Gala apples, as do all Honeycrisp apples, etc. We planted three Ashmead’s Kernel trees and only one still survives so the survival of this tree alone does not provide compelling evidence that a juglone-resistant variety of eating apple exists.
But, but, but. But apparently apples and walnuts grow together in Kyrgyzstan. Not black walnuts and not commercial apple varieties but genus malus and genus juglans apparently co-exist there in relative harmony (Greenman, 2014). Orchardist and blogger Eliza Greenman has speculated about the possibility that this could be happening due to presence of soil bacteria capable of degrading juglone rather the existence of an apple variety with juglone tolerance. In her blog, she points out that such a bacteria has already been identified and isolated (Schmidt, 1988).
Could the presence of a specific type of soil bacteria explain the success of our basswood tree and the survival of this isolated Ashmead’s Kernel tree? Is it possible that such a bacteria could be present on the north side of our site and not the south? Could intentional soil inoculation with this kind of bacteria make an integrated black walnut / heritage apple treescape possible? We don’t know.
But we know that we don’t know, and that’s the first step.
Black Squirrel Farms strives for accuracy but everyone makes mistakes sometimes. We’re happy to update our information if needed. Please contact us if you spot an error or have a suggested edit, update or information inclusion. Help is welcome.
Greenman, Eliza, 2014. “How in the heck can apples and black walnuts grow together? A thought”. Unconventional Stories from an Apple Farmer blog, https://elizapples.com/2014/11/24/how-in-the-heck-can-apples-and-walnuts-grow-together-a-revelation/
Orange Pippin Ltd., 2022. “Ashmead’s Kernel apple”. https://www.orangepippin.com/varieties/apples/ashmeads-kernel
Schmidt, S. K., 1988. “Degradation of Juglone by Soil Bacteria”. Journal of Chemical Ecology, Vol. 14, No. 7, 1988, https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.500.8621&rep=rep1&type=pdf