Gather 12 bundles of six 9-inch stems, two bundles of four 12-inch stems, and one bundle of four 15-inch stems. Secure each with floral wire just below the heads and at the ends. Pair up the 9-inch bundles, ends-to-heads, and wire them together, so you have six 9-inch bundles. Do the same for the 12-inch ones, so you have one bundle (again with heads fanning out at both ends). The one 15-inch bundle will have heads at only one end.