I get a square of light fusible interfacing and iron it to the wrong side of the jeans to hold the edges in place. Then I sew crossways across the rip back and forth. It takes quite a bit of stitching. I use the darning stitch on my sewing machine, but as long as you just sew back and forth pretty close together, about an inch or so each side of the rip it will work fine. I find that a charcoal grey thread seems to be more invisible than a blue thread. It isn't totally invisible, but the pants are wearable and mostly it doesn't show that much.

When doing this type of repair, I usually put a grey bobbin in and blue thread on top; I loosen the tension just a little tiny bit....the colors from the bobbin and the upper thread blend well into the fabric.

Kathy in Jax