Is it necessary to dead head carnations?

Cut the spent flowers (deadhead) to keep the plant neat, promote growth (especially stem branching) and get a rebloom in the fall. Take care to nip off the spent flower, not the whole stem. If you look further along the stem, you will see tiny flower buds forming to take the place of the spent one, if given the chance. If a carnation goes to seed, it focuses its energy in developing the seeds instead of flowers. It is more efficient to multiply carnations asexually through cuttings or divisions, so there's no need to let the flowers go to seed.