I am ready to start my next quilt and will be using flannel that I have in fat quarters. My question is how do I prewash? Won't it fray too much? If I pink the edges will that be good enuf? Do you think I could piece the backing and then wash it? I just don't want to make another mistake today....I've already met my quota of oops.

I always clip the 4 corners of my fabric before I prewash...then between the washer and dryer, I pull off/clip off any threads that are loose. I don't know why it helps to clip the corners, but it does. The only fabrics I prewash anymore are flannels, as they have a higher rate of shrinkage.
I do have a friend who always serges the edges of her fabrics before prewashing-so that is another option.

I am one who washes EVERYTHING when it comes in my house...including flannel. I guess I have been lucky but all of mine has washed beautifully without too much raveling. Maybe I should say raveling "within reason"???? Hope that makes sense.

how about just putting them in the sink in very hot water, then drying?

If you have a serger, it takes only a very few minutes to go around the raw edges.

Then there is no worry about losing a lot of threads due to fraying/raveling.

I didn't prewash flannel and it shrank so much it pulled the seams out and ruined the whole quilt.... PREWASH FLANNEL ALWAYS

I agree with sewing the edges. I don't have a serger so I just zigzag them. My sister washed a whole lot of flannel and spent about an hour separating them and cutting strings!

Stick it in one of those net bags made for washing undies, then they won't fray.

I don't buy flannel in FQs because of its shrinkage factor and yes, I always prewash flannel. The idea of the washing net is a good one.

I also would machine stitch your edges before washing. Either serger or regular machine. I think even just a straight stitch would be fine. You'll probably be trimming to straighten anyhow or at least have the stay-stitching in your seam allowance. ALWAYS wash your flannel. It was recommended to me when I first started quilting to wash everything in the hottest water you could and dry it on the highest setting so you get as much shrinkage out of the way before you start working on a project. I also recently heard from a quilt shop instructor (who sews everything from quilts to clothing and everything in between) that you really don't get the full benefit of the washing/drying process if you don't have a full load going into the dryer. If you're only drying a few bits of fabric the dryer is not running as long (unless you use a specific timed setting) and therefore doesn't get as hot. Actually made a lot of sense to me.