Black Walnuts are not good company for other plants as they produce juglone, a chemical that inhibits growth. Avoid all members of the rhodie family and also all hydrangeas. What may thrive are woodland flowers such as sweet woodruff, hardy cranes, and bill geranium. Daylilies, hosta, asters, and coralbells are also tough enough to survive. Members of the euonymus family such as the winter creeper evergreen euonymus, can give winter color. Spring blooming bulbs will survive but for some reason not crocus bulbs. Add some compost when you plant and don't be discouraged - planting under walnuts may be a tough nut to crack but worth the effort. Keep growing, Marianne Binetti