From Steve Nix,
Your Guide to Forestry.
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Black walnut used to be a very common old-growth forest tree. Black walnut wood is now relatively scarce and highly coveted, used mainly for high quality woodworking. The tree hates shade (intolerant)and best growth occurs in a sunny open location and a moist rich soil, common along stream banks in its native habitat.
The Black Walnut produces a substance that is toxic or "allelopathic" to other plants called juglone. Tomatoes and coniferous trees are especially sensitive. This mild toxin helps the tree keep other vegetation from competing or valuable nutrients and moisture.
Black Walnut grows with a rounded crown to about 70 feet (can reach 100 to 150 feet in the woods) and spreads 60 to 80 feet when open grown. The tree grows rapidly when young but slows down with age and develops with a number of massive branches well spaced along the trunk forming a very strong, durable tree. While valued as a lumber tree it may not make the best yard tree. The nuts are edible but are a nuisance to clean up and leaves often fall prematurely from some types of leaf disease.

Start with the Tree Finder if you are not sure what kind of tree you have!
The Silviculture of Black Walnut