Black Walnut Trees (Juglans nigra) make excellent landscaping trees for attracting wildlife and providing shade. The nuts they reliably produce each fall are also nutritious and tasty to those who don’t mind husking and cracking them! But anyone experienced in gardening knows that some plants cannot grow near Black Walnut trees. So, you need to do a bit of research before you begin landscaping or gardening around Black Walnut Trees. In this article I will tell you about
- The chemical secreted by Black Walnut roots that kills the plants
- I will provide a table / list of vegetables, trees, and flowers that known to be sensitive to Black Walnut
- Additionally, I will provide a table/ list of what vegetables, trees, flowers that have been shown to NOT be sensitive to Black Walnut trees
My reasoning for writing this is article is because I have at least one Black Walnut tree in my backyard. Although it is somewhat away from our backyard micro-prairie. However, we are expanding the prairie to plant some more natives, and they will be within the drip-line of the tree. Not wanting to try to fight Juglone poisoning from Black Walnut, I’ve been scouring the web to find documented cases of plants that can, and cannot grow in the presence of Juglone. I thought I would pass on the comprehensive list of plants that are poisoned by the Black Walnut Tree / Juglone. As well as the plants that should survive and not be affected by Juglone.
Juglone – The Poison from Black Walnuts
Juglone is chemically known as 5-Hydroxy-1,4-naphthoquinone or C10H6O3, is present throughout all parts of the Black Walnut Tree. But the roots of Black Walnut will secrete Juglone, contaminating the soil. So, plants that are sensitive to Juglone will either not grow well, or die if planted under the canopy. Some plants can be killed or inhibited if planted within 50′ of the canopy / drip-line of the Black Walnut Tree.
How much Juglone is in the soil, and how does it degrade?
Studies have shown Juglone concentration to decrease by as much as 80% just 4.25 m (15 ft) from the tree canopy. But one should exercise caution, as the sensitivity of plants to Juglone will vary species to species. Furthermore, the amount of Juglone in soil varies seasonally. There are certain bacteria that can feed solely on Juglone, which is likely a large component of the variation. So, the bacteria known as Pseudomonas putida J1 was found to to break down Juglone rapidly if soil was aerated.
Special Note – Black Walnut Trees can Help Fight INVASIVE PLANTS
US Forestry Service has conducted studies examining the sensitivity to Juglone on numerous plants, and I read it in researching this article. What really jumped out at me was that we could be using Black Walnut Trees in the fight against Invasive Plants! They found numerous invasive plants, depending on Juglone concentration, were severely inhibited in seed germination. All seedlings eventually died once the concentration of Juglone reached high enough level. This really makes me happy in that we have a natural ally in the fight against invasive Amur Honeysuckle!
Plants that are Sensitive to Black Walnut Trees
So, I have researched a number of universities and websites in an attempt to compile a full and comprehensive list of plants that have been documented to be sensitive to Black Walnut Trees. So, I’ve done my best to compile a number of informal lists from Kansas State, Iowa State University, University of Wisconsin, and Penn State. The good news is that the pretty much agree with one another, the only exception being I found Arborvitae on both a ‘sensitive’ and ‘tolerant’ list for different sites. So approach Arborvitae with caution. However, without further ado, here are the lists;
Comprehensive List of Plants Sensitive to Black Walnut Tree Toxicity
You can click on the image to expand it. It should be a nice size for printing!
Comprehensive List of Plants Tolerant to Black Walnut Tree Toxicity
Below are the lists I’ve compiled of vegetables, flowers, trees, and shrubs/vines that can tolerate Black Walnut Trees and the Juglone the roots secrete. Again, I made this after scouring various websites, but primarily off of University Extension sites. I found the Universities to be the most thorough, as you would expect.
So that is it! Now, feel free to use this as a reference to help you landscape around your Black Walnut Trees. These can be great shade trees that really bring in a lot of wildlife, and are even beneficial to pollinators. Below I will link to all of my references used in making this list (I don’t think I missed any).
Iowa State University
University of Wisconsin
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