I heavily starched my wall hanging, do I need to wash it out or when do I wash it out?, before I sandwich it, or after it is quilted.

It will much easier to quilt with the starch in. I always wash my quilts after they are finished and before I give them away to remove starch, markings, and to make sure they are colorfast.
Since starch can be used to adhere fabric to walls I think it would be safe to leave in in the wall hanging.

I wouldn't wash it until it is bound. If you try and wash it before it is finished, you could end up with fraying and distortion.
The starch won't hurt anything while quilting or binding, if anything you may find it to be very helpful :D:D:D

I don't wash it out of wall hanging-helps them hang flatter. When I give one as a gift, I let the recipient know there's starch in it and I'll wash it first it they want me too.

I never wash my wallhangings and I always use starch they hang much flatter with starch . I always recommend that my recipients starch after washing

Thank you all for your help, I'm leaving the starch in and see how it goes.