To make the dye solution:
Chop plant material into small pieces and place in a pot. Double the amount of water to plant material. If the pot is half full of plant material, then fill the pot with water. Bring to a boil, then simmer for about an hour. Strain. Now you can add your fabric to be dyed. For a stronger shade, allow material to soak in the dye overnight.
Getting the fabric ready for the dye bath:
You will have to soak the fabric in a color fixative before the dye process. This will make the color set in the fabric.
Official Patent Website: http://www.uspto.gov/web/p
Salt Fixative (for berry dyes) 1/2 cup salt to 8 cups cold water
Plant Fixatives (for plant dyes) 4 parts cold water to 1 part vinegar
Add fabric to the fixative and simmer for an hour. Rinse the material and squeeze out excess. Rinse in cool water until water runs clear.
Dye Bath: Place wet fabric in dye bath. Simmer together until desired color is obtained. The color of the fabric will be lighter when its dry. Also note that all dyed fabric should be laundered in cold water and separately.
Muslin, silk, cotton and wool work best for natural dyes and the lighter the fabric in color, the better. White or pastel colors work the best.
NOTE: It's best to use an old large pot as your dye vessel. Wear rubber gloves to handle the fabric that has been dyed, the dye can stain your hands. It's also important to note, some plant dyes may be toxic, check with the Poison Control Center if unsure