Q: I have some loblolly pine acreage with an easement road down the middle. I‘m considering planting black walnut trees on both sides of the road for my grandchildren to sell the lumber and for wildlife. How far should the trees be separated from the pines to avoid damage due to juglone produced by walnut tree roots?
A: Contrary to what I and other garden experts have written previously, it turns out that walnut trees are not always allelopathic to other plants. For every mention that black walnut is harmful to a particular plant, there seems to be another observation that no harm was done to that plant by a nearby walnut tree. In a laboratory, juglone was shown to inhibit some plants, but laboratory tests are not nearly the same as landscape conditions. Some species of pine have been demonstrated to be harmed by walnut tree roots. So your safest bet is to have the walnuts around thirty feet away from your pine trees.