Black Walnut Tree - Knowledgebase Question

Norristown, PA
Question by sml610
May 2, 2001
I have a Black walnut tree that seems to have rendered fruitless the surrounding black raspberry bushes. If I take out the bushes, what flower, vegetable, herb, or other plant could I put in that would not also be killed off? The tree is also now so large that whatever I put in will get partial or full shade.


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Answer from NGA
May 2, 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 tree is 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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