There are multiple ways of doing stems. My favorite method is to use a Clover bias tape maker. I heavily starch the fabric before cutting and then cut stems on the bias. I run a pointed end through the Clover tool to get it started, place my iron on top of the fabric coming out, and iron the folds as they come out of the tool. Fast, easy, and works great for me. When getting ready to sew on (I use invisible machine applique methods), I pin all the inner curves first to keep them flat; the bias stretches to fill out the outer curves. I would typically applique the leaves in place first, then do both sides of the stem (covering the leaf ends), and then applique the flower last to cover the raw end of the stem.