Black walnut (Juglans nigra) produces juglone and related compounds. Some plants perform poorly within the walnut root zone, but juglone is not the only possible cause: dense shade, dry soil, root competition, drainage, disease, and herbicide injury can produce similar symptoms.
Where Risk Is Highest
Juglone occurs throughout the tree, with higher concentrations reported in roots, buds, and nut hulls. Problems are most likely under the canopy and wherever living or decaying roots occupy the soil. A mature tree's roots may extend beyond the dripline, so distance from the trunk is only an estimate.
Removing a walnut does not remove all roots immediately. Sensitive plants may still be affected while root pieces decay, and large-tree removal has cost, safety, shade, and habitat consequences.
Plant-Tolerance Lists Are Starting Points
Extension lists are built from observations and reports made under different soils and climates. A species described as “tolerant” is not guaranteed to thrive; a plant described as “sensitive” may fail for several interacting reasons.
Plants Commonly Listed as Sensitive
- Tomato, pepper, eggplant, and potato
- Blueberry and some other fruit crops
- Azalea, rhododendron, lilac, and selected ornamentals
Plants Commonly Reported as More Tolerant
- Beans, corn, carrots, beets, onions, squash, and selected other vegetables
- Ferns, coral bells, sweet woodruff, and selected shade-adapted perennials
Cultivar, soil, drainage, irrigation, tree size, and root contact can change the outcome. Confirm choices with a local extension source and test a small number of plants before committing an entire bed.
How to Plan a Garden Near a Walnut
- Map the site. Note the trunk, canopy, likely root zone, sun hours, irrigation reach, and wet or dry areas.
- Choose the least risky location. Put sensitive vegetables and fruit as far from the walnut root zone as practical.
- Use containers when separation matters. Large containers with clean media provide more reliable root separation than a shallow raised bed.
- Manage raised beds realistically. A deep bed with a durable root barrier can delay root entry, but barriers need inspection and may not remain effective indefinitely.
- Keep fresh hulls and roots out of sensitive beds. Follow local guidance before using walnut leaves or chips; thoroughly composted material behaves differently from fresh debris.
- Trial and record. Note plant, cultivar, distance, light, soil moisture, and results over more than one season.
Diagnosing Wilting or Yellowing
Check soil moisture at root depth, sun exposure, drainage, roots, vascular discoloration, insects, disease signs, and recent chemical use. Do not assume juglone from location alone. A local extension office or plant-diagnostic clinic can help distinguish toxicity from wilt disease, root rot, drought, or herbicide injury.
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?