Although the deep tap root makes the tree drought tolerant, its surface roots do not like to be disturbed.
Thus, deep digging around the tree may weaken its tolerance to disease and insects.
If you can plant somewhere where the soil has been disturbed, leave the stable ground in its natural state.
All these have been seen to grow under Black Walnut.
Plums
Pears
Grapes
Garlic
Leeks
Onions
Squash
and Cherry
(Ref: PermacultureCollaborative.us Paula Westmoreland, PRI Cold Climate Beta Plant Database)
Daniel Halsey
SouthWoodsForestGardens.blogspot.com
Permaculture and Polyculture Design
“Treat the earth well: it was not given to you by your parents; it was loaned to you by your children.
-Native American Proverb