Black Walnut Survival Guide

Don't panic if you are trying to garden under a Black Walnut (Juglans nigra).  As you have undoubtedly discovered, there are some plants, like tomatoes, that absolutely will not grow under these fine large trees.  There are even more plants that will thrive there.  You just have to arrange your garden carefully and be aware of a few guidelines for experimentation.

The problem with Black Walnuts is a substance called juglone, which is emitted by the roots, nuts, leaves, and branches of the tree.  Juglone is toxic to many plants.  If you use Black Walnut chips for mulch, they will carry juglone.  When the leaves drop in early fall, these leaves can also cause problems for juglone-sensitive plants.  If you remove a Black Walnut, the soil will contain juglone for at least 1 year, and maybe as long as 5 years (depending on the source of the information) and thus will not be a good place for you to plant susceptible plants.

Be very observant when you are weeding.  Squirrels love walnuts and will bury them anywhere and everywhere.  You might find seedlings growing up in planting beds quite far from the parent Black Walnut tree.  These seedlings pose the same threat as the parent tree.  Juglone does not dissolve readily in water and thus does not move through the soil with rainfall.  So, once the 1-5 years has passed, you should be able to plant without fear.