Answer: There's a growth inhibitor within the bark, roots, leaves, stems and fruits of walnut trees. Some plants are more tolerant of this than others, and will grow near walnut trees. Other plants are extremely sensitive and will not grow. Other considerations to make when planting under walnuts is that the trees have shallow root systems and do not like competition for moisture and food from other plants. A final consideration is that walnuts like their roots on the dry side, and many other landscape plants need more water than is healthy for walnut trees. Pines and spruces are both listed as sensitive to juglone (the growth inhibitor from walnut trees) and would not thrive if planted near walnuts. Some alternate choices with similar growth and appearance are Arborvitae, Viburnum, Forsythia, Redbud, Black Locust.
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