The bias cut of the strips allows you to mold the vines into the shape you need because the bias edges can be stretched. Typically what you want to do is secure an inside curve first (with a pin or glue or basting stitches) so it lies flat; the bias on the outside can then be stretched to lie flat along the outside curve line. If you do the outside curve first, you may find there is too much vine fabric on the inside curve.