Answer: Black walnut (Juglans nigra) has a reputation for being allelopathic -- that is, for inhibiting the growth of other plants. Small amounts of a substance called juglone are released by the tree roots, but a far greater amount of this growth-inhibiting chemical is found under the canopy of the tree.
Some plants that are tolerant to juglone include arborvitae, cedar, catalpa, clematis, daphne, elm, euonymous, forsythia, hawthorn, hemlock, sycamore, astilbe, begonia, bellflower, orange hawkweed, hosta, pansy, phlox, marigold, primrose, snowdrop, sweet woodruff, trillium and zinnia.
Avoid plants that are sensitive to juglone, including apple, blackberry, pear, blueberry, asparagus, cabbage, eggplant, pepper, potato, and tomato. Landscape plants sensitive to juglone include azalea, birch, honeysuckle, hydrangea, larch, lilac, magnolia, maple, pine, potentilla, rhododendron, spruce and viburnums.
You can also try growing juglone-sensitive plants in containers filled with purchased potting soil.
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