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
Siacr8, the highest amount of the juglone is in the roots, nut hulls, and smaller branches. There is less amount in the leaves and actual bark. Plus the compost has been cooking for 4 years. I think you are ok. Just do not put any old roots, nut hulls and such as mentioned into your pile.
Mixed some old composted woodchips and bark from various trees from a pile that was at least 4 years old..as im sifting after mixing it into my yard compost i am finding old whole black walnuts..most chips turn to dirt/dust when squeezed..but ive collected this added material from the bottom of the piles..and raspberries and most vegetables are already in a diluted mix of this…have i killed my tomatoes and raspberries? Too much conflicting info available..confused..should i go for it or abort while its early? Im in mendocino county in northern california.
Victoria, What I have read is that the roots can exude juglone as they decay for several years. So if you want to plant right away, you should go with plants that are not sensitive to the juglone. The other option is to wait for a couple of years for the roots to decay.
Victoria, What I have read is that the roots can exude juglone as they decay for several years. So if you want to plant right away, you should go with plants that are not sensitive to the juglone. The other option is to wait for a couple of years for the roots to decay.
Removed a storm damaged walnut tree last fall and the root ball will be removed in a few weeks. We want to plant evergreens or some other tree that will hide the buildings behind in the space that the walnut and its roots were. How long before the soil is “clear” of the toxins and we can plant without fear our investment will die?