Dianthus flowers (Dianthus spp.) are desirable for their heavily ruffled blooms and long life as cut flowers. Whether or not they come back each year depends in part on which species you have and your climate. Many are simply not disease resistant or cold hardy enough to bloom every year. Others are tender perennials or biennials, meaning they live for two years.
The Dianthus genus of flowers is large. Species in the genus include carnations (D. caryophyllus), maiden pinks (D. deltoides), China pinks (D. chinensis) and sweet William (D. barbatus). The latter two are classified as annuals by the University of Illinois Extension, which means they usually bloom for only one growing season and die after the first hard frost of autumn. This can vary according to growing zone, however. Maiden pinks are considered perennials. Carnations are tender perennials -- they come back each year in U.S. Department of Agriculture growing zones 6 through 9 only.
Climate plays a big part in whether or not your dianthus plants will come back each year. In Illinois, for example, sweet Williams are considered annuals, but they often overwinter in Arkansas, according to the University of Arkansas Division of Agriculture. This means that they go dormant during cold weather and bloom again in the spring rather than being killed entirely by frost. In general, repeated hard freezes kill dianthus plants, and so will very hot temperatures. For these reasons, dianthus plants are most likely to return and bloom again year after year in temperate climates and in well-draining soil.
Diseases can also prevent dianthus plants even in temperate climates from continuing to bloom. Anthracnose is a fungal disease that spreads on water and can kill most dianthus plants, although sweet William seems to be immune. Symptoms include yellowed leaves and wilting of the plant. Drip irrigation can cut down on the spread of the disease, as can careful handling of already-diseased plants.
Insect pest infestations may also prevent dianthus plants from blooming again in the spring. Aphids in particular can plague these flowers. These sucking insects leach the juices from the new, tender leaves and buds. Grasshoppers also love to munch on some dianthus species, as do slugs and snails.