The dead flowers of a Dianthus can be removed after blooming on tall stalk plants. Mounding varieties should be trimmed back below the point of flowering. Removing the faded blooms encourages further blooming. A Dianthus can be encouraged to bloom past midsummer with this treatment.
After the first killing frost, cut back the Dianthus to a height of 1 or 2 inches above the soil. If the leaves of the Dianthus plant are turning brown during growing season, it is likely that overwatering is the cause. This plant needs less than an inch of water per week. If the plant is producing fewer flowers than in previous years, it should be divided. Dianthus should be divided in early spring before blooming every three to four years.
Dividing a plant is accomplished simply by digging up the root ball and then inserting a trowel through the center of the plant and roots. Replant both halves in the desired locations at least 12 to 14 inches apart. Replant the flowers at the same depth as the original plant, and do not bury stems or leave exposed roots.
Dianthus prefer a rich slightly alkaline soil that is well drained. These plants require full sun, at least four to six hours per day.