Living in a rural area of Eastern Oregon, the countryside is dotted with large groves of old walnut trees that were planted by many of the original settlers. This high concentration of Black Walnut trees in our area probably accounts for the numerous times that we are asked the same question at our farm, Stargazer Perennials "What can you grow under a Black Walnut tree?"  Well for all of you who have Black Walnut trees, here's the answer.
The roots of walnut trees and specifically black walnut trees produce the toxin juglone which can make gardening around them difficult. The toxin juglone resides in large amounts in the tree's roots and is known to inhibit respiration, resulting in stunted or deformed growth, and even death, in juglone-sensitive plants.

What can you do: First, avoid tree removal if at all possible! Cutting down your Black Walnut trees is not a good solution to your landscaping woes as long as your tree is healthy. Juglone is not very water soluble and will stay in the soil (and any tiny feeder roots not removed) for several years. Black Walnut trees provide wonderful shade, reduce CO2 while providing fresh oxygen, produce food and shelter for backyard wildlife and birds, and make an excellent windbreak due to the strength of their wood.

Second, just like gardening with deer, you have choices when it comes to gardening around Black Walnut trees. Here is a list that we have complied over time of plants that can be grown successfully under Black Walnut trees: pansies, violets, daylilies, hosta, sedum, squash, melons, beans, carrots, corn, snap peas, mints, forsythia, narcissus, astible, monarda and black raspberries.