The Plant Edit
Black walnut is native to the central and eastern United States. It prefers well-drained soil in lower altitude and usually occurs in mixed forests. It is widely planted in the United States, Europe, and other temperate regions of the world. The black walnut tree can usually grow to 130 feet (40m) tall. Trees should not be planted in areas which experience a late frost. 
The leaves and the fruit husk are most commonly used for dyeing. However, the bark and heartwood can be used as well.
How to Harvest Edit
Black walnuts can be gathered from the ground under the trees from September through October. The nuts can be cracked and the meat of the nut can be eaten. Husks are easiest to remove while fresh, and should be handled with rubber gloves, to prevent skin staining.  It is also suggested that walnuts be collected while still green and then dried.  Leaves can be picked and used fresh or dried for later use. Bark and wood, likewise, can be used fresh or dried for later use.
How to Extract Color Edit
All parts of the tree contain a substantive dye, so it is not necessary to mordant to obtain a strong, lasting color. Mordanting will produce additional shades, particularly with chrome, copper, and iron. Leaves should be soaked for at least 24 hours to extract color.The husks can be soaked for 24 hours and can be left in a bucket of water for up to several months.  Black walnut dye can be processed with a low water temperature or by a sun tea method. It can also be brought to 82°C (180°F) and simmered for 20 minutes or more to achieve the desired shade. Adding alum will give richer shades of brown. Iron will create rich beiges, browns, and blacks.  Avoid boiling for an extended period, as walnut can effect the quality of the wool. 
- ↑ 1.0 1.1 Cannon, J., & Cannon, M. (1994). Dye plants and dyeing (pp. 30-31). Portland, Or.: Timber Press.
- ↑ 2.0 2.1 Duerr, S. (2010). The handbook of natural plant dyes: Personalize your craft with organic colors from acorns, blackberries, coffee, and other everyday ingredients (pp. 71-73). Portland, Or.: Timber Press.
- ↑ 3.0 3.1 Furry, M., & Morrison, B. (1935). Home dyeing with natural dyes. Washington, D.C.: U.S. Dept. of Agriculture.