black walnuts - Knowledgebase Question

Canton, Oh
Question by craigburdet
June 30, 2010
I have numerous black walnut trees and know some items will grow close o them and others won't. I have even noticed my grass has a problem in some ares where there has been an abundance of walnuts. Is there a list of what will grow and what will not? Is there an answer to my grass asa well?


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Answer from NGA
June 30, 2010

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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.

Turfgrass is reasonably tolerant, as long as you remove the fallen nuts as soon as possible. If you allow them to remain and the husks begin to decompose, the juglone will be released and can remain in the soil for extended periods of time. So, the answer is to keep the leaves and fallen walnuts raked up. Good luck with your landscape!

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