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
Pauline, the toxicity can persist for years until all of the roots have decayed. The farther away from the stump the better. I do not see an Autumn Gold Ginkgo listed but the list is pretty basic. If the arborist said it was ok then it probably is. Might want to ask the nursery that you purchased the tree. They may have a better idea.
I just had a 45+ year old walnut tree removed a week ago and now what to plant about 5-8’ away from stump grounded. I want to plant an Autumn Gold Ginkgo that is about 8 feet tall. Is this safe to do? The arborist stated it would be. Or is it better to wait and how long? Warranty is only good for a year.
David, I did not find any information on borage and whether or not it does ok near walnuts.
I seem to recall reading somewhere that Borage is another plant that does fine planted near Black Walnut trees; in fact, it was recommended as a cover crop. However, now that I try to find that info again, I cannot.
Does your experience confirm this: Does Borage grow fine beside Black Walnuts?
Deb, from everything I read the toxicity can persist in the area the tree was located for several years as the roots decay.