Dianthus can be propagated by taking cuttings from the mother plant or by sowing seeds.
From cuttings
Take a cutting: In mid-summer, cut a 2–3 inch segment from a non-flowering shoot of the mother plant.
Prepare the cutting: Remove the lower leaves of the cutting. You can also dip the cut end in rooting hormone.
Plant the cutting: Insert the cutting into a pot of moist potting soil mixed with vermiculite. Make sure at least one node is below the soil.
Place in a warm, sunny location: Keep the soil moist but not soggy.
Wait for new growth: After about a month, new leaves should appear.
Replant: Once the cutting has new growth, you can transplant it to its permanent location.
From seeds
Annual dianthus varieties are usually propagated by seed.
Dianthus can spread by self-seeding, about a foot from the parent plant.
Dianthus prefer well-drained, neutral to slightly alkaline soil. They can tolerate clay, silt, or sandy soil, but over-watering can cause root rot and yellow leaves.