Black Walnut - Knowledgebase Question

Milford, MI
Question by wconaway
May 23, 2001
I have a yard full of Black Walnut trees. Will either of these plants survive if they are within 20 feet of the black walnuts? 1) WANATABI Viburnum PLIC Tomemtosum, 2) WENTWORTH Viburnum Trilobub, Dr. Merrill Magnolia, 3) Cherokee Princess - White Dogwood, 4) PAWPAW, 5) Southerh catapla, 6) Fothergilla, 7) Sweet Mock Orange.

Thank you!


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Answer from NGA
May 23, 2001

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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. Since your walnut trees are there to stay, try to plant one of the less-susceptible plants in the vicinity of the trees roots or canopy.

Avoid plants that are sensitive to juglone, including apple, blackberry, pear and 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.

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