Combine your plant material and water and bring to a boil, turn off the heat and let it sit overnight. Remember if you’re doing yellow or red don’t boil the plant material too long. Some material may not take as long to release its color as others, and some material such as bark or pine cones may need to be soaked overnight before you begin. Keep checking on it until you get the desired color. Strain the plant material out. Dissolve the alum and cream of tartar in a small amount of hot water and stir into the dye solution until thoroughly dissolved. Add your fabric. Soak the fabric in the dye solution overnight or until it reaches the desired shade. Hurrying the process will only lead to disappointment. The mordant and dye must be given a sufficient amount of time to deeply penetrate your fabric. The dye solution may be used again and again until it no longer yields the desired color. Dye solution can be stored for later use, but if not refrigerated it will produce mold.
If your results are not exactly what you expected try again with more plant material, a different part of the plant, or another plant altogether. Plants do not read books and do not always behave as the references state. There are many variables in dyeing that can affect the end product so be patient and adventurous.
When washing your naturally dyed fabric, or clothing, it is best to wash it by hand with mild detergent because too much time in the washing machine with harsh detergent will fade your dye.