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Plants:Black Walnut Toxicity

Black Walnut Toxicity

Black Walnut ToxicityOccasionally, clients will call our offices with complaints about an area in their yard where nothing seems to grow. One of the questions we ask is “Is there a Black Walnut tree nearby?” Black Walnut (Juglans nigra) and a related species, Butternut (Juglans cinerea) produce juglone, a substance that is poisonous to a wide variety of plants. The problem exists in all areas of the soil around these trees.

Black Walnut and Butternut trees are not recommended for use in residential landscapes because of the difficulty in growing other plants nearby. They are best suited to wide-open, natural areas where their beauty and fast growth rate can be appreciated, their nuts can provide food for wildlife, and where they will not interfere with the health of other desirable plants.

There may be other plants that can be grown in place, but the study of this subject is not complete and new additions to the list are discovered periodically. Even experts disagree occasionally about whether a plant should be included. This is not scientific research, it's observation.

Black Walnut ToxicitySymptoms of Black Walnut Toxicity

The symptoms of juglone poisoning include yellowing or browning of the leaves of affected plants, stunted, twisted growth or a failure to grow, sudden wilting and death. As walnut and butternut trees grow larger and their roots spread, sensitive plants further and further away from the main trunks of these trees will begin to decline in health and may eventually die.

Not all plants are affected by this toxicity problem. Some plants have a natural resistance to juglone and can survive near and even under walnut and butternut trees. Some plants do not grow deep roots, and more shallow root systems seem to be more resistant as well.

Juglone is present in all parts of black walnut and butternut trees. Care needs to be taken when disposing of the nuts, bark and leaves of these types of trees. Do not use these materials for mulch around plants that are not tolerant of juglone.

Plants Not Recommended Near Black Walnut Trees

TREES
Silver Maple Acer saccharinum   Apple, Crabapple Malus spp.
Black Alder Alnus glutinosa   Basswood, Linden Tilia spp.
White Birch Betula spp.      
 
CONIFERS
Japanese Larch Larix kaempferi   White Pine Pinus strobus
Norway Spruce Picea abies   Scots Pine Pinus sylvestris
Mugo Pine Pinus mugo   Yew Taxus spp.
 
SHRUBS  
Red Chokeberry Aronia arbutifolia
Cotoneaster Cotoneaster spp.
Hydrangea Hydrangea spp.
Lilac Syringa spp.
Potentilla Potentilla spp.
Azalea, Rhododendron Rhododendron spp.

Additional Resources

Black Walnut Toxicity

Wisconsin Natives Plant Guide (pages 21-22)


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