The buttonhole stitch is different than the The blanket stitch. I would not do a button hole stitch. I would stitch around the appliques before quilting using a small zip zag. I personally don't like zig zag or buttonhole stith showing on the back. I would do light interfacing and turn the edges of each leaf. Not a fan of raw edge, then use a hemstitch, -----v---v---v (best I can do on graphic) before quilting. (then quilt around the leaves).