The shells are encased in a mushy greenish-yellow husk that stains. The Navajo blended the shells with alum to make a dark brown dye. Black walnuts are more strongly flavored than Persian walnuts, and higher in protein. They are commonly used in cookies, and can be used as a meat substitute in many dishes. Ideal commercial spacing for timber production is 10-15' apart, thinning every other tree after 20 years.
Walnut oil tastes good.
The tree often grows over 100 ft. tall. Black walnuts have lacy compound leaves, arching limbs and deeply ridged, dark grey bark. The leaves can be up to two ft. long, with 15 to 20 leaflets. The nuts are yellow, green, or in-between. Cultivation Seedlings and some cultivars are not self-fertile, or not significantly so.