Juglans nigra better known as Black Walnut produces a toxin call juglone. The toxin is poisonous to most plants that might grown under a Black Walnut. Below is a list of plant material that might grow successfully under a Black Walnut. These plants have been tested and show promise. However, there is no guarantee they will be successful in every situation. Planting under a black walnut often requires trial and error.

Tolerant Plants
Acer
Ajuga
Cercis
Clematis
Crataegus
Eunonymus
Forsythia
Leucanthemum
Hemerocallis
Hosta
Pachysandra
Polygonatum odoratum
Syringa
Viburnum

These are links to more information about black walnuts.

Walnut Toxicity

Walnut Trees and Soil Toxicity

Black Walnut Toxicity