The dianthus plant is also called Sweet William (Dianthus barbatus) and has a fragrance with cinnamon or clove notes. The plants are small and usually between 6 and 18 inches tall.nstructions on how to care for dianthus are very straightforward. Water the plants when dry and apply fertilizer every six to eight weeks. You may also work a slow-release fertilizer into the soil at planting, which will release you from the need to feed the plants.