I've inherited a compost pile that is under a black walnut tree. I would be a dolt if I use it for flowers and tomatoes, correct.?
Nope, not a dolt!
Ohio State University looked into the matter and the reply is yes: juglone decomposes within weeks in contact with air, water and bacteria. If the leaves are shredded, decomposition is even quicker. And once decomposed, walnut leaves apparently give a compost of excellent quality.
Walnut sawdust and wood chips as well as walnut husks, however, are slower to decompose: it is best to compost them for 6 months before using them in the garden to be sure the juglone has thoroughly decomposed.