Black Walnut Toxicity Explained: What Not to Plant Near a Black Walnut Tree and the Best Juglone-Tolerant Companion Plants
Black walnut trees (Juglans nigra) are valued for shade, timber, and nuts—but they can be challenging for gardeners. Black walnut produces juglone, a natural compound that can injure sensitive plants, especially within and near the tree’s root zone. If you’re searching “what not to plant near a black walnut tree” or wondering why plants struggle under a walnut tree, this guide covers the basics, the most common juglone-sensitive plants to avoid, and reliable options that tend to tolerate juglone.
Quick Answer: What Not to Plant Near a Black Walnut Tree
Most often damaged (avoid under the canopy/dripline and within the root zone):
- Nightshades: tomatoes, potatoes, peppers, eggplant
- Other vegetables often listed as sensitive: asparagus, peas, cabbage-family crops (varies by site)
- Fruits/shrubs often listed as sensitive: apples, blueberries, blackberries (and other brambles)
- Ornamentals often listed as sensitive: azalea, rhododendron, lilac
Usually better choices (commonly listed as juglone-tolerant):
- Vegetables: beans, corn, carrots, beets, onions, squash, melons, parsnips
- Ornamentals/groundcovers: hosta, ferns, coral bells, sweet woodruff
- Tip: If you must grow sensitive plants nearby, use deep raised beds with clean soil and keep walnut debris out.
Understanding Black Walnut Tree Toxicity (Juglone)
What is juglone?
Juglone (5-hydroxy-1,4-naphthoquinone) is an allelopathic compound produced by black walnut. It occurs in many parts of the tree—especially roots and nut hulls—and can inhibit growth in certain sensitive plants. Toxic effects are usually strongest under the canopy/dripline, where roots and leaf/hull debris are most concentrated.
How far does juglone reach?
Many university and arboretum resources describe the highest risk within the dripline and the broader root zone, with effects sometimes reported roughly 50–80 feet from a mature tree depending on conditions. The key takeaway: the closer you garden to the trunk and under the canopy, the more likely sensitive plants will struggle.
Is it juglone—or shade and dry roots?
Not every “failure under a walnut tree” is juglone. Dense shade, dry soil, and root competition can also cause wilting, yellowing, and stunted growth. If a plant fails repeatedly only near a black walnut (but thrives elsewhere), juglone sensitivity becomes more likely.
What Not to Plant Near a Black Walnut Tree
The plants below are frequently cited as juglone-sensitive. Sensitivity can vary by variety, soil drainage, rainfall, and distance from the tree, but these are the most common “avoid” picks for gardens located under a black walnut canopy or within the root zone.
| Category | Often Sensitive / Higher Risk Near Black Walnut |
|---|---|
| Vegetables | Tomatoes, potatoes, peppers, eggplant; asparagus; peas; and some cabbage-family crops (site dependent) |
| Fruits & berries | Apples; blueberries; blackberries/other brambles (especially within the canopy area) |
| Ornamentals | Azalea, rhododendron, lilac (commonly listed as sensitive) |
Workaround: If you want to grow sensitive plants “near” a black walnut, build deep raised beds (or use containers) with juglone-free soil and keep walnut leaves, hulls, and twigs out of the bed.
Best Black Walnut Companion Plants (Juglone-Tolerant Options)
Many plants grow well near black walnut. The best approach is to choose species commonly listed as juglone-tolerant and then match them to the site conditions (shade, moisture, and root competition).
Vegetables commonly listed as juglone-tolerant
Trees & shrubs that are often reported as tolerant
- Elderberry, persimmon, plus many established landscape trees (examples often include oaks and some maples depending on the site).
Perennials, groundcovers & shade-friendly companions
- Sweet woodruff, Shasta daisy, hostas, coral bells, and ferns
For more planting ideas, browse potted trees and shrubs suited to mixed plantings.
How to Successfully Garden Near Black Walnut Trees
- Start with distance: Place sensitive plants outside the canopy area and as far from the trunk as practical. The dripline is the highest-risk zone.
- Use raised beds (the right way): Build deep beds with clean soil and keep walnut leaves, hulls, and twigs out of the bed.
- Clean up debris: Rake and remove fallen leaves and husks to limit juglone buildup where you’re trying to garden.
- Manage shade and moisture: Most sites under walnut are dry and shaded—pick shade-tolerant plants and water deeply when establishing new plantings.
- Trial before you commit: Try a small test planting with a “tolerant” species list before installing a full bed.
If you’re gardening under partial shade, this guide can help with light management: protect plants with shade cloth.
Conclusion
Black walnut doesn’t have to mean a barren garden. With smart plant selection, careful debris management, and raised beds where needed, you can build a productive, juglone-aware planting plan that works around your walnut tree. For more planting inspiration, browse walnut trees and plan your landscape with juglone in mind.
71 comments
I have 2.5 acres completely filled with black walnut. The understory is almost entirely Amur honeysuckle, other trees are hackberry, box elder, locust and a couple of white pines.
The hackberry and Amur honeysuckle are thriving and do not seem walnut sensitive.
John, if the leaves start to decompose, then yes they could be adding juglone to your soil. You can rake them up to keep the exposure down. But not much else you can do, other than garden in raised beds, away from the walnut tree.
I have had a 16 by 24’ garden plot for at least 12 years on our side yard with a walnut tree as close as 28’ from the garden. A branch does hang just about over the end of the garden. The first few years the garden was very productive without any issues until juglone began to do a number on especially tomato plants. Had 10 yards of soil removed about five years ago and new soil added after I put down heavy duty black plastic as a barrier against the roots. The garden did great for two or three years and the problem has intensified again. I always clean the garden in the fall by removing dead plants, leaves, etc. before I put down several hundred pounds of manure from a local farmer that raises chickens, steers and some hogs, and other animals for children to visit. Would some leaves laying on the soil for a month or so create the juglone and would possibly puncturing through the soil with some wire tomato holders and wooden stakes also create toxicity from the soil. I have no option to move the garden, but I could add a few raised beds further away from the closest of the two walnut trees. Would appreciate any suggestions in dealing with this ongoing juglone problem. This year it appears to have impacted not only the tomato plants, but also the beans and zucchini plants unless there are other issues do to a spell of heavy rains and then a short heat wave. Thanks.
Do not eat veggies that are growing in the area of a walnut tree. The juglone can be toxic to humans.
First grass yellowed and die
All of the vegetables got moldy as died
The Black walnut tree would bloom,drop seeds and then the top drop off where it blooms.
Can you eat vegetables that Juglone has rained on or roots growing along this tree?