Will black walnut fertilize carpathian walnut, and vice versa?
Marion County Indiana
Thank you for your question to eXtension.
I do not believe black walnut (Juglans nigra) will pollinate the English/Persian (Capathian) walnut (J. regia). They are two different species, and as such, should not be able to pollinate each other.
According to Purdue's publication on Fruits and Nuts for Edible Landscaping (http://www.hort.purdue.edu/ext/HO-190.pdf ), black walnuts must have a second tree for pollination, but the English/Persian walnut is partially self-fruitful. This means that one English walnut, by itself, will produce some fruit (nuts), but production is much higher if there is a second variety nearby.
Please let me know if you have any other questions.