If you are starting to plan the Sashing process for your Dear Jane quilt then you may find my Sashing tutorial helpful. I wasn't looking forward to sewing all the sashing at the end so decided to do it as I finished my blocks.
I wrote these instructions on my main blog 2 years ago. If you follow my instructions you will need approximately 2-1/2 yards of fabric for your sashing strips.
This doesn't include the fabric for your scallops. You will need an additional 2-1/2 yards of fabric to make those if you use my method. (we'll cover the scallops in a few months)