I wash all my fabric by hand as soon as I buy it, gently but in very, very warm soapy water. It's mainly to get rid of any excess dye that the odd red or green will have. And if they are starting to throw a bit of dye I will make it hot water. And to let it shrink a bit if it wants to. I only buy at the quilt shops, and I find that it is surprising to find out what materials you won't be buying anymore and what are lovely. I don't think of it as a chore but as a getting to know you kind of exercise....