Once again it is time to point out the importance of proper fabric preparation when dyeing with natural dyes. I don't say this to be rude but rather to save you much time and effort when dyeing cotton with natural dyes.
Q. Do I have to scour my PFD, Prepared for Dyeing, Fabrics?
A. YES you must scour PFD fabric before mordnating and dyeing with natural dyes, I go as far as even washing BEFORE I scour my fabric to ensure that the dressing oils, all fabrics receive these it's to keep the dust down when the fabric is rolled onto bolts, tubes, etc.. I have scouring instructions on my website and video on youtube. The scouring process is so very important with cellulosic fibers as it helps to force the fibers open before the mordanting and dyeing steps. Scouring ensures that your fabric will hold maximum natural dye molecules and helps to achieve truer colors.
Q. is your water hard or treated? Water quality is very important regarding the final dye color out come. Hard water tends to supress most dye molecules (exception is weld it becomes more intense).
Q. Which plants do you plan to dye with? Some plants do not yield permanent color so it is important to know this before you start a project, as depending on your plans for the fabric you may not be able to over dye at a later date if your colors fade.
NOTE: Also cotton fabrics don't take certain natural dye colors no matter what you do to the fabric but silk and wool fabrics will suck the color up like no tomorrow.