It has been well documented for centuries that some plants either struggle to grow near Black Walnut Trees, or are outright poisoned by them . The toxic chemical the possess is called Juglone. Some plants are either stunted, die, or can’t germinate near Juglone.
Based on dozens of Journal Articles and University Ag Extensions, I’ve compiled a comprehensive list of 42 flowers, trees, and vegetables that can’t grow near a Black Walnut Tree. They will struggle to grow, or die if planted within 20-25′ of the dripline of a Black Walnut Tree.
Why Does the Black Walnut Tree kill other plants?
The Black Walnut Tree secretes a chemical from it’s roots, fallen leaves, and husk of the black walnut known as Juglone. This chemical gives the Black Walnut Tree (Juglans nigra) an allelopathic effect , killing certain plants that are within it’s canopy .
What is Allelopathy?
Allelopathy is where a plant secretes a chemical that will inhibit the growth of surrounding plants. Allelopathy is a neat evolutionary characteristic that some plants use to reduce competition. Think about it, if a tree can kill all surrounding plants, then it gets all the sunlight and soil nutrients.
As with any evolutionary process, some plants have been documented to be tolerant of Juglone. These plants can grow near, or within the canopy of a Black Walnut Tree. You may be interested to read the 201 different species of plants that are Juglone tolerant, and can grow near Black Walnut Trees.
Vegetables, Flowers, and Trees that Should NOT be planted near Black Walnut Trees!
|Number||Plant Type||Common Name||Scientific Name|
|8||Vegetables||Tomatoes ||Solanum spp|
|9||Flower||Blue False Indigo||Baptisia spp|
|13||Flower||Flowering Tobacco||Nicotiana alata|
|17||Flower||Lily of the valley||Convallaria majalis|
|21||Flower||Crimson Clover||Trifolium incarnatum|
|22||Shrub / Vine||Blueberry||Asparagus officinalis|
|23||Shrub / Vine||Black Berry||Brassica spp|
|24||Shrub / Vine||Mountain Laurel||Cucumis sativus|
|25||Shrub / Vine||Grapes||Solanum melongena|
|26||Shrub / Vine||Amur Honeysuckle||Lonicera maackii|
|27||Tree||Apple Trees||Malus spp|
|29||Tree||Black Alder||Alnus glutinosa|
|33||Tree||Eastern White Pine||Pinus strobus|
|36||Tree||Mugo Pine||Pinus mugo|
|37||Tree||Norway Spruce||Picea abies|
|38||Tree||Red Pine||Pinus resinosa|
|39||Tree||Scots Pine||Pinus sylvestris|
|40||Tree||Silver Maple||Acer saccharinum|
|41||Tree||White Birches||Betula papyrifera|
|42||Tree||Russian Olive||Elaegnus angustifolia|
How long does Juglone poison stay in the soil after cutting down a Black Walnut Tree?
So, if you remove a Black Walnut Tree and want to start a garden, fear not! 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.
So, if you cut down a Black Walnut Tree in your yard, you will likely be able to begin planting flowers / trees / shrubs after removing a tree. It will just take some time for the bacteria to break down the Juglone in the soil.
 – Pliny the Elder, AD23-79. https://extension.illinois.edu/blogs/garden-scoop/2018-08-23-black-walnut
 – I. Kocacë Aliskan & I. Terzi (2001) Allelopathic effects of walnut leaf extracts and juglone on seed germination and seedling growth, The Journal of Horticultural Science and Biotechnology, 76:4, 436-440, DOI: 10.1080/14620316.2001.11511390
 – Brown, Diane. Growing vegetable gardens near black walnut trees. Michigan State University Extension. Retrieved 29OCT2020.
 – Schmidt SK. Degradation of juglone by soil bacteria. J Chem Ecol. 1988 Jul;14(7):1561-71. doi: 10.1007/BF01012522. PMID: 24276429.
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