Set a dozen carnations in a vase of water overnight. This allows the flowers to stay fresh longer in the arrangement.
Soak a 4-inch heart-shaped floral foam in a sink full of water for at least 10 minutes to completely saturate. Set aside on a dish drainer to let excess water drain off.
Remove the carnations from the vase of water and cut the stems to 1 inch in length at a 45-degree angle. Cutting on an angle allows the flowers to absorb more water and last longer.
Glue craft moss over the floral foam to cover the top and sides. Insert the carnations into the foam covering the top. The flowers should be close together.
If hanging the carnation arrangement on a wall, hot glue a 10-inch piece of ribbon to the back of the heart-shaped foam, forming a loop. Hang the arrangement by the ribbon loop.